When ordering a few quarts of ATF for an Asian or European vehicle that rolls into your shop, you might ask yourself,”Why are there so many types of automatic transmission fluid?” While catering to specific car-maker demands can be a challenge, staying current with manufacturer recommendations is a must for today’s shops.

There are two reasons why there are so many transmission fluid variations. First, automakers are changing the internal components of the automatic transmission to improve fuel efficiency and shift quality, so the transmission fluid plays an even greater role. Second, the shift to longer maintenance intervals has influenced the levels of certain ingredients in the base stock, contributing to even more transmission fluid formulations.

The Role of Transmission Fluid

Transmission fluid performs several roles inside the transmission. First, it lubricates and cools the transmission’s internal components. Second, it acts as a hydraulic fluid to actuate the planetary gears in the torque converter for the fluid coupling. Third, it controls the friction characteristics of the clutches. A very special fluid is required to cover all of these important tasks.

By volume, the base stock is the No. 1 ingredient in automatic transmission fluid, and it’s produced from crude or synthetic oil. The base stock is highly refined and processed with solvents so the molecules are uniform and engineered to meet certain viscosity and lubrication specifications. The manufacturer will mix and “tune” the fluid for each specific formulation. Additives are added to the base stock to further change the properties of the automatic transmission fluid.

Friction modifiers are also added to increase the lubricity of the base stock. This allows for smoother engagement of the clutches and bands. Depending on the level of friction modifiers, engineers are able to better control chattering or shuddering during the engagement of the clutches and bands inside the transmission. The friction materials on the clutches and the shear forces specific to the transmission design dictate the level of friction modifiers used.

Other additives are incorporated to help the fluid withstand the extreme pressures inside the transmission and to prevent wear on the inside of the transmission.

Evolving Transmissions

All automatic transmissions experience power loss. When the transmission shifts by locking planetary gears, engaging clutches or closing solenoids, power that would have gone to the wheels is lost. These power losses impact the efficiency of the transmission and the engine.

Every year, the OEMs experiment with new designs to increase the efficiency of their automatic transmissions. Small changes to the clutches, valve body and operating temperatures can add up quickly to stress current fluid specifications. Even a small change in how fast a solenoid opens or the angle of the stator’s blades in the torque converter can require a change in the fluid to prevent foaming and cavitation.

In addition, new transmission technologies like CVT and nine-speed configurations may require a proprietary transmission fluid formulation. These unique transmissions may only be in production for a few years, but they will still require service for decades. This is why it’s important that you verify in your service information that the transmission fluid you are about to use is the correct one. This is very important, considering that for certain import applications, there might be up to five different automatic transmission fluid specifications.

Interval Increase

Twenty-five years ago, the service interval for transmission fluid was around 30,000 miles. Today, the typical interval is more than 100,000 miles. This interval increase is the result of the reformulation of transmission fluid base stocks and improvements to additive packages.

The main enemy of transmission fluid is oxidation that occurs when the transmission fluid is heated and becomes stressed. Oxidation breaks down the base stock’s carbon chains. When a fluid is oxidized, it will have a burnt smell. The additive package of extended-interval automatic transmission fluids has higher levels of additives that prevent oxidation. Buffer additives are mixed in to control the pH of the fluid. Another type of additive known as a surfactant helps the base stock adhere to the surface and encapsulate small particles. But, these additives can be depleted and degrade over time.

When you are replacing or topping off automatic transmission fluid, you need to make sure you are using the correct application. If the bottle says, “For use in VW vehicles,” you need to look at the label and check the manufacturer’s website to be sure it is appropriate for the specific transmission, not just the year and make.

The transmission game has changed. Solenoids, sensors and computers have replaced vacuum lines, governors and kick down cables on modern automatic transmissions. The tools have also changed: Scan tools, scopes and meters have replaced pressure and vacuum gauges.

Even with codes and datastream information, you must be able to think like the transmission to find the correct diagnosis, which typically doesn’t involve replacing the entire transmission.

Thinking like a modern transmission means understanding what information the transmission has, how it interprets that information and how it uses the information to select the correct forward gearing. You also have to understand how the transmission prioritizes performance when it is compromised.

Rule 1: The Modern Transmission is Info Hungry

On earlier models, once the throttle cable was pulled so far, or a switch under the gas pedal was activated, the transmission would kick down to the next, lower gear.

The modern transmission is much more complex. When the driver presses the gas pedal, the request goes to both the engine and transmission control modules. A transmission control module or software may look at 30 different parameters to determine gearing and torque converter settings.

On most late-model vehicles, the transmission is on one of the faster serial data buses or an exclusive bus that ties it to the engine controller and maybe one other controller. Some use one module to control both the engine and transmission.

The module craves information, and it uses this information to make the best possible shifts — shifts that are efficient, smooth and cause the least possible wear to the components inside the transmission.

The control module uses information beyond the calculated engine load, throttle position and input/output speeds. Some control modules will look at mass air flow (MAF) sensor and engine temperature information to determine the correct shift points and line pressures.

Relying on this extra information helps the transmission sense additional problems, such as malfunctioning crankshaft position sensors, high engine temperature and even clogged air filters.

If any of this information is missing or outside of operating parameters, the control module will throw up a red flag and set a code. Depending on the discrepancy, the control module might conclude that the problem could damage the transmission and, in turn, reduce power or go into a limp mode as a response.

Rule 2: Modern Transmissions are Programmed to Save Themselves

Instead of letting a transmission destroy itself due to a malfunctioning component, a controller will put the engine and transmission into a safety mode to save the wear components. A limp, failsafe or reduced power mode are conditions a driver can’t ignore.

Customers will notice their speed is limited or their engine is not allowed to rev beyond a preset rpm limit. Internally, the transmission may increase line pressure and change shift points, with some transmissions skipping gears to prevent further damage to the clutch pack.

A multitude of conditions cause a safe mode, including a failure to communicate on a data bus, a failed sensor or a bad shift. The code is just the starting point, not a final diagnosis. Most automatic transmissions will only engage second gear if it detects a problem.

Rule 3: Modern Transmissions Adapt to Wear, a Driver Does Not

A modern transmission is programmed to deliver seamless shifting. Having more gears helps, but how those gears are controlled makes the biggest difference. The goal is to engage and disengage clutch packs smoothly, but as a transmission wears, the engagement behavior can change.

How the transmission determines a shift point is similar to a closed-loop feedback emissions system that still uses short- and long-term fuel trims. When an automatic transmission shifts gears, it looks at the input and output speeds to determine the quality of the shifts.

While changing gears, the transmission may detect a flare in engine rpm that does not produce a change in vehicle speed. The control module will register this as a bad shift and recognize that the clutches are slipping with the current shift program. The control module will then make changes to the shift timing or line pressure in order to eliminate the gap during the shift. This will prevent damage and slipping in the torque converter clutch.

If a clutch is gripping too harshly, the control module may see a sudden drop in rpm with little change in vehicle speed. The control module will then change how the clutches are engaged. Most modern transmissions will set codes if they can’t compensate anymore or if there is a sudden change in clutch performance.

This adaptation mechanism can also adapt to the condition of the transmission fluid. If the fluid is the wrong specification or has degraded to the point that it’s changing the friction levels of the clutch, the computer will adapt and change the shift behavior.

But this adaptation feature can only mask the problem for so long, and it can create other problems. For instance, if the module controlling the transmission loses the shift information because the battery was disconnected or the module was replaced, then the transmission will revert to factory settings that do not include the adjustments for clutch wear. So, a minor battery replacement could leave customers accusing you of damaging their transmission.

There are a few methods for recalibrating the transmission control module. You can drive the car or let it run with the wheels off the ground (some ABS/traction control systems won’t allow you to do this), or you could use a scan tool if the calibration protocol calls for it

Late-model vehicle technology is changing. Wider tires, active safety systems and AWD technology are not only influencing how vehicles perform, but also the service and maintenance requirements of their functional fluids.

Power Steering Fluids

OE Interval: 60,000-100,000 miles

What has changed? Wider wheel and tire packages are putting more strain on power steering systems. More strain on the pump and rack means more heat. This heat can degrade the power steering fluid and eventually damage the seals and internal surfaces of the pump and rack.

Customers need to be aware there is no such thing as universal power steering fluid, as many models use specific formulations that are compatible with the seals in the system. A low fluid level is a sign that there is a leak. But, topping off with what is available at the gas station can do more harm than good, in some cases.

Some new power steering fluids on the market are designed to reduce the pump’s drag on the engine. If the wrong fluid is installed, it could damage the pump and the rack.

Brake Fluids

OE Interval: Based on the age of the fluid.

What has changed? ABS, ESC and traction control have become standard on most vehicles sold during the past decade. When the system activates to either release or lock a wheel, the hydraulic control unit’s valves can be hard on the brake fluid. The high pressure and force exerted on the fluid can degrade the fluid and also degrade the additive package and base stock.

The brake fluid is designed to have a specific viscosity, so when a valve opens the brake fluid flows as expected. But, water contamination and changes to the additive package can change the viscosity. In some cases, worn out brake fluid can cavitate and cause air bubbles in the fluid when it’s forced through the valves.

Transmission Fluids

OE Interval: 80,000-125,000 miles

What has changed? In the past, the fluid would be replaced only when the customer detected a change in how the transmission shifts. But, modern transmissions can mask worn fluid by changing shift points and line pressures. However, even the most sophisticated computer algorithm can mask worn out fluid for only so long. Eventually, the original fluid’s viscosity changes and depleted friction modifiers can damage the clutches and bands. This can destroy a transmission.

Transfer Cases and Differentials

OE Interval: 60,000 to “lifetime”

What has changed? More vehicles are equipped with AWD transfer cases and differentials with electronically limited slip, locking and torque vectoring technology. They have new fluid requirements and service intervals, so ignoring a maintenance interval could lead to an expensive repair.

Some transfer cases and differentials have a lifetime factory fill and do not require service. If they leak and lose even a small amount of fluid volume, it can be catastrophic for the component.

Fluid requirements for these components can be very specific and require exact levels of friction modifiers to get the electronically actuated mechanical components to function properly.

When a piston accelerates downward after the ignition of the fuel and air, the crankshaft speeds up and then slows down as it reaches the bottom of the stroke. These changes in speed are minimal, but big enough to cause problems.

If the pulses are not minimized, they can hammer the belt and the attached rotating components. On a four-cylinder engine, the degrees of rotation between power pulses are greater than on a V8. This means the amount of change in speed on the four-cylinder pulley is greater than on a V6 or V8. This has a direct effect on how the belt system is designed.

Some of the forces can be taken up by the belt slipping on the pulleys. But, slipping causes friction and wear on the belt, as well as flutter. Over time, the slipping can get worse as removal of material from the ribs causes the belt to bottom out.

There are three components that help to keep the belt on the pulleys without slipping. The tensioner, harmonic balancer and decoupler pulley work together to keep the accessory belt system quiet and the belt lasting until the replacement interval.

Harmonic Balancer

The harmonic dampener puts a layer of soft material between the crankshaft and outer ring of the pulley. The material helps to dissipate the power pulses and resonant frequencies. While the dampener may only flex one or two degrees of movement, this takes a lot of strain off attached components.

Tensioner

The tensioner applies force on the belt. Some tensioners have devices that dampen the movement of the spring and arm. The tensioner helps to keep constant force on the belt even under a wide variety of conditions.

Decoupler Pulley

Some alternators have a decoupler pulley. This device serves two purposes. First, it helps to decouple the pulley from the alternator with a one-way clutch. The decoupler reduces parasitic losses by not having to fight against the momentum armature alternator while the engine is decelerating and accelerating. Some decoupler pulleys have a spring and friction dampener to reduce vibration. When an alternator decoupler pulley is compromised, it can no longer absorb the same level of abuse, which has a trickle-down effect throughout the system.

Alternator decouplers and pulleys should be inspected every 10,000 miles for wear. Early design versions have a service life of 40,000 to 60,000 miles, with more recent versions lasting more than 100,000 miles.

When inspecting a decoupler or pulley, there are two signs that replacement is needed. First, after shutting down the engine, if there is an audible buzzing, the bearings in the pulley have likely failed. The second sign depends on whether the vehicle has a one-way clutch (OWC), overrunning alternator pulley (OAP) or decoupler (OAD).

With the inspection cap/cover removed and the center locked, turn the pulley or decoupler with the appropriate tool. If it is an OAP or OWC, the pulley can only be turned in the clockwise direction. If it is an OAD, a counterclockwise turn will reveal a noticeable increase in spring force; a clockwise turn will only have slight resistance.

The tensioner, harmonic balancer and decoupler pulley work together to keep the belt in contact with grooves in the pulleys. The three components are engineered together to match the engine. If one part is compromised, all are compromised, including the belt.

Non-Transmission Sensors Causing Transmission Complaints

Most transmission control modules use inputs from other sensors on the vehicle. If a vehicle can’t accurately calculate the load on the engine, it will adjust the line pressure and slippage to the inaccurate calculation.

Sensors used to calculate the load can include the Manifold Air Pressure (MAP), Mass Airflow Sensor (MAF) and Throttle Position Sensor (TPS). If unmetered air is entering the cylinder through a leak, the engine load will be below the actual percentage causing the module to use different shift points and line pressures. This could cause the transmission to delay shifts, overheat, and possibly burn the fluid.

Maintenance items like a dirty air flow meter, blocked crank case ventilation system, or restrictive air filter can change the calculated engine load to the point where it can influence shift points and shift quality.

Wiring Harness Problems

The wiring harness and connectors on most transmissions operate in a unique environment. Normal automatic transmission fluid’s conductivity is very low. Hybrids usually have a specification for a fluid that is non-conductive. In most cases, the fluid will not damage or short the connections; the detergents and chemicals will cause the degradation of the materials in the wiring harness that might be outside of the case.

Also, check for any damaged wires and connections that could be damaged by weak or shifting motor mounts, hot exhaust systems, and impact with road debris.

Grounds 

The grounds for solenoids and sensors have changed dramatically since the mid-1990s. Never assume the chassis ground is coming through the valve body or case. Before trying to diagnose a dead or open solenoid, study the wiring diagrams. Some transmissions can have multiple ground points for the module, sensors, and solenoids.

There are many “mechatronic” parts that control and protect the traditional clutches and planetary gears in modern automatic transmissions. These devices shift the gears, lock the clutches and regulate the fluid pressures.

 Tool Up

When overhauling and diagnosing transmission units, you will often need special tools. Back when transmissions where purely mechanical and hydraulic, all you needed was a set of high-pressure gauges to check line pressures. You also needed a vacuum gauge to check the engine’s intake vacuum and the integrity of the vacuum modulator. But with today’s electronic controls, you need a scan tool, scope, and a multimeter.

Transmission codes and sensor data on late-model vehicles is accessed through the OBD II diagnostic connector and the Powertrain Control Module (PCM) diagnostic gateway module. But on some vehicles, the information is often found in a separate Transmission Control Module (TCM) or Body Control Module (BCM). Either way, you’ll need a scan tool to access fault codes and operating data.

A scan tool can also help you check for communication faults between the PCM and transmission controller if the vehicle has separate computers. Problems here will typically cause the transmission to go into a “limp in” mode that may lock it in 2nd gear.

Some electronic transmission problems may or may not set a fault code and turn on the MIL lamp, so it’s important to always scan the PCM or transmission module for codes if there’s a transmission-related complaint or driveability issue. Some engine sensor failures can also affect the operation of the transmission. So, these sensors should also be checked.

If you find a transmission fault code, you may have to check the resistance of a solenoid in the valve body, its operating voltage or the­ ­frequency of its control signal from the ­computer. This will require a digital multimeter (DMM) that can read voltage, resistance and ­frequency or dwell.

You’ll also need the applicable service information that includes wiring schematics and OEM diagnostic charts with test specifications for all the components that need to be checked. This kind of information can be found in OEM service manuals, on OEM websites (daily one-time access fees are typically $15 to $25), or through online technical information service providers. You should also check for any technical service bulletins (TSBs) that may be related to the transmission problem. In some cases, it may be necessary to reflash  the PCM or transmission module to cure a particular fault.

Diagnostic Strategies and Transmissions

It’s often what is not displayed on the scan tool that will lead you to your final diagnosis when using a scan tool to diagnosis a drivetrain problem. The modern transmission is one of the most connected components on a vehicle. If a PCM or TCM can’t see inputs like engine speed, load or throttle position, it will assume the worst and put the transmission into a safe or limp mode.

The transmission does not have discreet sensors connected to the throttle body, crankshaft or intake manifold. Instead, the transmission shares information with the engine control and other modules in the vehicle using a serial data bus. Most vehicles manufactured after 2004 put the TCM or PCM module on the hi-speed two-wire CAN network along with BCM and ABS modules.

The topology for these networks is typically a loop. If a module is not operating, the existing modules can still communicate on the bus. When you’re using your scan tool to solve a transmission problem, you may have to look at the PIDs or datastream from the ECM or BCM to see what modules are talking on the bus.

If you can’t communicate with a transmission control module with your scan tool, look for transmission information in the connected modules. The BCM will monitor information from the TCM on gear position so it can tell the instrument cluster what gear to display for the driver.

It can also work the other way. If a TCM is not able to communicate with the ECM, looking at the transmission-related PIDs for calculated engine load, throttle position and manifold air pressure may show that the ECM is not communicating on the network.

Did you ever wonder how automatic transmissions ­became a specialty, separate from general auto repair?

The transmission was a completely separate entity from the rest of the vehicle for the first 40 years or so since automatic transmissions began rolling off the assembly line .

Back then, if the transmission wasn’t shifting, you could be pretty sure you were dealing with a transmission problem. If another part of the vehicle wasn’t working correctly, they wouldn’t have any real effect on transmission operation.

All that changed with the introduction of computer control. Suddenly a hint of corrosion on a battery terminal could create just as many transmission problems as a warped valve body or leaking clutch seal.

Suddenly, transmission repair lost its independence from the rest of the vehicle. Transmission technicians had to become acquainted with engine performance, computer controls, electrical diagnosis and more.

Why did manufacturers include transmission operation in their computer control systems? Computer integration added hundreds — if not thousands — of dollars to the cost of today’s cars. So how did it benefit the manufacturers?

The Benefits of Computer Control
In the late ’70s and early ’80s, auto manufacturers were faced with a new mandate: They had to improve gas mileage while reducing emissions.

They addressed these challenges by using computers to control engine operation, through more intricate electronic ignition and fuel injection. But, it wasn’t enough. Engine control could only improve vehicle performance so much. They needed more. Much more.

To make the next giant leap in performance, they needed to wring more efficiency out of the drivetrain. This included lockup torque converters and overdrive gear ratios.

They tried using mechanical controls for those enhancements, but they weren’t responsive enough to maintain the transmissions’ integrity. They often failed quite spectacularly.
So to provide the level of control necessary for these newer, more efficient transmissions, manufacturers turned to computer controls. These new computer control systems were able to adjust to momentary fluctuations in load, speed and driver demand.

Thanks to these computer systems, we’re now seeing lockup converters eliminating drivetrain slip as early as second gear. Overdrive gear ranges are part of the norm, with units showing up with up to seven forward drive ranges. Even the Constantly Variable Transmissions (CVT) are finally able to withstand the demands of normal driving conditions.

The new control systems enabled today’s cars to offer higher gas mileage and lower emissions without sacrificing performance. Today’s transmissions shift faster and smoother, while providing an acceleration boost at the slightest touch of the throttle.

Further integration with today’s ABS systems has enabled today’s computer systems to help control traction, reducing skids and providing additional stability on all road conditions.

What’s more, the rapid response provided by these computer controls has improved transmission durability. With a little care and some basic maintenance, many cars can go over a quarter million miles without needing a major transmission repair.

Did You Know…
Under certain conditions the transmission will go into some kind of limp-in or “default” mode. When a serious fault is diagnosed (such as loss of an internal speed sensor signal) or a problem ­occurs in the wiring circuit to any of the shift solenoids, the Traction Control Module (TCM) will kill the power to the transmission control relay and de-energize all of the shift solenoids.
This usually causes the transmission to freeze in second or third gear. The transmission will remain in limp-in mode until either the problem is diagnosed and repaired, or power to the TCM is momentarily turned off to “reset” the computer. This may restore normal operation temporarily, but as soon as the TCM detects the fault again, it will go back into limp-in mode.

A New Transmission Technician
Of course, any technological advance places additional demands on the technicians who repair them. Yesterday’s transmission rebuilder has had to adapt to this new level of integration, forcing him to consider much more than just the transmission when presented with a shifting problem.

Where yesterday’s top rebuilders could deal with most diagnoses using a vacuum and pressure gauge, and maybe a test light, today’s technicians need to be comfortable with a scan tool, a digital multimeter and even a digital oscilloscope.

As most transmission technicians will acknowledge, more than half of the cars with “transmission” problems that show up today have absolutely nothing wrong with the transmissions themselves. The problems are caused by any number of sensors or systems within the vehicle that can affect the operation of the engine, brakes, steering, suspension…and the transmission.

These changes have virtually redefined the transmission repair industry from how we knew it just a few years ago. But the tradeoffs in performance and ­efficiency are well worth the extra effort.

Multiple Vehicle Systems Can Affect Transmission Operation
OBD II, which stands for Onboard Diagnostics, second generation, is a diagnostic standard that was mandated in 1996 for all cars sold in the United States. It was designed to reduce confusion by instilling a level of uniformity to today’s cars: standard diagnostic connectors, standard communication protocols, standard naming conventions, standard diagnostic codes, and so on.

All of which was designed to make it easier to diagnose today’s cars. With OBD II systems, you can use a common scan tool for diagnosis, and when you order parts, the component names should be the same across vehicle lines.

One of the standards is code arrangement. OBD II codes all have five digits. The first digit is always a letter, which designates the system the code relates to, such as “B” for body control and “P” for powertrain.

The next digit will be a zero or a one. Zero denotes a generic code and a one indicates it’s a proprietary code. Generic codes are predefined and mean the same thing for every manufacturer. Proprietary codes are defined by the manufacturer, and are unique to that manufacturer. The last three digits are the code itself.

So a P0734 means a fourth gear ratio error, regardless of which car it came from, because the second digit is a zero, which represents a generic code.

On the other hand, P1734 was assigned by the car manufacturer, so it can mean something different for each manufacturer. That means P1734 from a Ford could mean one thing, and from a BMW it could mean something entirely different.

But manufacturers try to stick with the generic codes whenever possible, or just create slight variations to some specifics for its codes. So a generic code list can come in handy if you can’t get your hands on the manufacturer’s code list.

There are a number of codes related directly to the transmission. These codes identify shift solenoid
problems or gear ratio errors. They’re pretty obvious to identify.

But many transmission-related problems arise from issues that might seem to have nothing to do with the transmission at first glance. For example, not only will a failed knock sensor cause problems with engine performance, but a lot of computer systems disable overdrive after detecting a knock sensor problem.

Don’t disregard those simple sensors when you have a transmission problem. Ratio errors, such as the P0734 mentioned earlier, can occur because of an alternator failure. Excessive AC interference from a bad alternator can travel through the electrical system and cause the computer to misread vehicle speed and RPM sensor signals.

Finally, old and tired batteries are notorious for affecting transmission operation.

Fault codes can be confusing at first, but they’re actually pretty simple when you break them down. Keeping the electrical system in good working order can head off a lot of aggravation too.

Remember to keep a generic code list handy. They’re not always as detailed as the manufacturer-specific codes, but most of the time they’ll get you headed in the right direction.

Sensors provide the inputs the Powertrain Control Module (PCM) needs to make critical control decisions. They are like the nerve endings of the vehicle. Without accurate input data, the computer may not make the correct command decisions. This, in turn, can cause emissions, performance and drivability problems.

Except for some early 1980s vintage oxygen sensors, most sensors have no factory recommended replacement intervals. They work until they don’t. In other words, they are designed to last the life of the vehicle or until they fail.

The Onboard Diagnostic (OBD II) system is capable of detecting most sensor faults if a sensor is not reading within its normal range or if the signal is lost altogether. If a fault is detected, the OBD II system will set a code and turn on the Check Engine light to alert the driver that something is amiss. In some situations, the OBD II system will set a “pending” code in its memory that does not turn on the Check Engine light, but will eventually turn the light on if the same fault happens on a subsequent trip.

 The Check Engine light is very confusing to most motorists because it doesn’t reveal anything about the nature of the fault. The motorist has no way of knowing if the problem is something serious or only a minor glitch. The only way to know what is causing the light to come on is to plug a scan tool into the diagnostic connector and read the code(s).

As a rule, the Check Engine light only comes on if a fault affects emissions. A bad sensor can certainly do that. However, the Check Engine light usually does NOT come on if the engine has quit running, if the engine is overheating, if the engine has a mechanical problem, if oil pressure is low, or if the oil needs changing.

Many motorists simply ignore the Check Engine light, especially if their engine seems to be running normally. But this is not a wise decision because some “minor” problems can have major consequences if ignored long enough. An engine that is misfiring because of a bad spark plug, weak coil, dirty fuel injector, leaky valve, or vacuum or EGR leak, may cause the catalytic converter to overheat and suffer damage. An engine that has a “lean” code such as P0171 or P0174 (which can often be caused by a dirty mass airflow sensor) is at greater risk of engine-damaging detonation when the engine is working hard under load.

Another reason for not ignoring the Check Engine light is that a vehicle with a Check Engine light on will fail an OBD II plug-in emissions test. There must be no codes present to pass the test. And if the vehicle doesn’t pass the required test, the vehicle owner can’t renew his vehicle registration when the license plate sticker expires.

To pass an OBD II emissions test, all of the OBD II system’s self-monitors must have run and completed before the vehicle is considered “ready” for testing. A bad sensor can prevent some OBD II monitors from running. An oxygen sensor code, for example, will prevent the catalyst monitor from running. The catalyst monitor needs good inputs from both the upstream and downstream O2 sensors to check the operating efficiency.

Oxygen Sensors

Oxygen sensors are one of the most often replaced sensors. Inputs from the O2 sensors are used by the engine management system to adjust the fuel mixture. This is critical for maintaining low emissions and good fuel economy. If an O2 sensor gets “lazy” because of old age or contamination, the computer may not be able to adjust the fuel mixture quickly enough as the engine’s operating conditions change. O2 sensors that are failing tend to read lean, which causes the fuel system to run overly rich to compensate. The result is increased emissions and fuel consumption.

The responsiveness of the O2 sensors can be tested using various procedures (making the fuel mixture rich or lean and watching the sensor’s response on a scan tool with graphing capability). If an O2 sensor is sluggish or unresponsive, it needs to be replaced. The same goes for any O2 sensor that has a bad internal heater circuit.

O2 sensor failures can be caused by various contaminants that enter the exhaust. These include silicates from internal engine coolant leaks (due to a leaky head gasket or a crack in a cylinder wall or combustion chamber) and phosphorus from excessive oil consumption (due to worn rings or valve guides). Replacing a fouled O2 sensor may temporarily solve the problem, but sooner or later the new sensor also will fail if the underlying problem that is allowing the contamination to occur is not corrected.

Identifying which O2 sensor has to be replaced also can be confusing. On most 1996 and newer V6 and V8 engines, there are at least two upstream O2 sensors, and one or two downstream O2 sensors. Some engines may have as many as six O2 sensors. A fault code for an O2 sensor will indicate the sensor location by sensor number (1, 2, 3 or 4) and by cylinder bank (1 or 2). Sensor No. 1 is usually the one in the exhaust manifold, while sensor No. 2 is usually the downstream O2 sensor behind the converter. Cylinder bank 1 is the same side that also has the number one cylinder in the engine’s firing order. Bank 2 would be the other side.

Replacement O2 sensors have to be the same type as the original with the same number of wires. If one O2 sensor on a high-mileage vehicle has failed, chances are the other O2 sensors may also be nearing the end of their service life and should be replaced at the same time to restore like-new performance.

Coolant Sensors

The coolant sensor keeps the PCM informed about the temperature of the coolant inside the engine. This is vital information for the PCM because many control functions vary with temperature. If the coolant sensor is faulty or is reading low, it can throw off the control system possibly causing it to remain in “open loop,” which is a temporary operating mode that should only occur following a cold start. A faulty coolant sensor, therefore, may cause the engine to run richer than normal, resulting in increased fuel consumption and higher emissions.

Input from the coolant sensor also is used to operate the engine’s electric cooling fan. No input or low input from the sensor may allow the engine to overheat because the fan isn’t coming on when it should be. Coolant sensors can be damaged by overheating, so if the engine has experienced an episode of severe overeating for any reason, replacing the coolant sensor is often recommended.

The coolant sensor’s output can be viewed on a scan tool as a temperature reading. It should match the air inlet temperature (IAT) reading when the engine is cold, and gradually increase as the engine warms up. The sensor’s resistance also can be checked with an ohmmeter and compared to specifications for various temperatures. If the sensor is not reading correctly, it needs to be replaced.

Throttle Position Sensors

The throttle position sensor (TPS) is mounted on the throttle body and monitors the position of the throttle opening. The TPS value is displayed on a scan tool as percentage of throttle opening. The PCM uses this information to estimate air flow and engine load. On newer vehicles with electronic throttle control, the sensor’s input also is vital for making sure the throttle is at the correct commanded position.

The PCM uses information from the throttle position sensor (TPS) to estimate air flow and engine load. Contact-style TPS sensors can develop a worn spot just above the idle position as the miles add up. This, in turn, may create a “flat spot” that results in momentary hesitation or stumble when the driver steps on the gas. This may not set a fault code because the glitch occurs too quickly for the OBD II system to detect.

The sensor’s out put can be checked with a voltmeter, or observed on a scan tool. If there are any drops in the output as the throttle opens, the sensor is bad and needs to be replaced. On some older vehicles, the idle voltage setting of the sensor must be adjusted to a specified voltage.

MAP Sensors

The Manifold Absolute Pressure (MAP) sensor monitors the pressure differential between intake vacuum and the outside atmosphere. The PCM uses this information to determine how much load is on the engine. If the engine has a “speed-density” fuel injection system that does not use a mass airflow sensor, input from the MAP sensor is also used with inputs from the TPS sensor to estimate airflow. Problems with this sensor can cause hesitation, fuel mixture and spark timing problems. The sensor’s output can be read on a scan tool, or checked by reading its frequency or voltage output on a DVOM. If the sensor is reading out of range, check the sensor’s connection to the intake manifold for a possible vacuum leak. If there’s no leak, the sensor needs to be replaced.

Mass Airflow Sensors

The Mass AirFlow (MAF) sensor is usually located between the air filter housing and the throttle. The MAF sensor uses a heated wire or filament to measure airflow into the engine. This is vital information for controlling the fuel mixture. The most common problem here is contamination of the sensor element with dirt or fuel varnish. A dirty mass airflow sensors will typically report less airflow than is actually occurring. This can cause a lean fuel condition, hesitation, and reduced performance. The sensor’s output can be observed on a scan tool and should go up as the throttle opens and airflow increases. A sluggish or unresponsive MAF sensor can often be restored to normal operation by cleaning the sensor element with aerosol electronics cleaner. **Do not use any other type of cleaning chemical as this may damage the sensor!** If cleaning doesn’t do the trick, the sensor needs to be replaced.

Crankshaft & Camshaft Position Sensors

The Crankshaft Position (CKP) sensor keeps the PCM informed about the relative position and rotational speed of the crankshaft. Many engines also have a Camshaft Position (CMP) sensor that helps the computer figure out the correct firing order of the engine. A failure of either sensor may prevent the engine from starting or running.

Two types of sensors are commonly used for these applications: magnetic sensors or Hall effect sensors. Magnetic sensors have a wire coil wrapped around a magnetic core. When the tip of the sensor passes over a notch on a ring attached to the crank, it changes the magnetic field and produces a small current. With Hall effect sensors, a reference voltage is supplied to the sensor by the PCM to detect notches in the crank wheel.

Crank sensors may be mounted on the front of the engine and read notches in the crank pulley or mounted on the block to read a notched ring on the crank itself. The cam sensor(s) if used, are usually mounted in the cylinder head(s) and read a ring on the camshaft(s).

Loss of a signal or an erratic signal will usually set a fault code. The resistance of magnetic sensors can be measured with an ohmmeter. If out of range, the sensor needs to be replaced. The sensor ring also needs to be inspected for damaged, missing or cracked teeth as any of these conditions can cause erratic sensor readings.

Speed Sensors

Most late model vehicles have several magnetic speed sensors. The Vehicle Speed Sensor (VSS) is usually located on the transmission output shaft and provides a signal that is proportional to vehicle speed. The transmission also has one or two additional internal sensors for monitoring the relative speeds of the main input and output shafts. On vehicles equipped with antilock brakes, there are usually Wheel Speed Sensors (WSS) to monitor each of the wheels.

Faults in speed sensor circuits usually tend to be wiring related rather than outright sensor failures. However, magnetic sensors can become fouled with iron particles that stick to the tip of the sensor. Sensor inputs can be viewed on a scan tool or checked by measuring their resistance with an ohmmeter. If the wiring is okay but the sensor is reading out of range, the sensor needs to be replaced.  On vehicles where the wheel speed sensor is an integral part of the hub and wheel bearing assembly, the entire hub must be replaced if the sensor is bad. The ABS system will not operate unless it has good signals from all of its sensors.

Temperature Sensors

The engine management system uses an Inlet Air Temperature (IAT) sensor to monitor air temperature because changes in air temperature affect air density, which in turn affects the fuel mixture. A sensor that is not reading accurately can upset the fuel mixture causing an increase in emissions and fuel consumption as well as drivability issues. The sensor’s output can be shown on a scan tool or measured with an ohmmeter. If out of range, the sensor needs to be replaced.

The heating ventilation and air conditioning (HVAC) system also use air temperature sensors to monitor air temperature within the passenger compartment. A bad sensor won’t turn on the Check Engine light because it does not affect emissions, but it can cause problems with regulating heating and cooling if it is out of range.

Tire Pressure Sensors

All 2006 and newer passenger cars and light trucks are equipped with tire pressure monitor systems (TPMS) to keep an eye on tire pressures. The system will alert the driver if pressure drops 25 percent or more below the recommended inflation pressure. Most TPMS sensors are mounted on the end of the valve stem inside the wheel, though some older systems use a large TPMS sensor attached with a steel band to the drop center inside the wheel.

TPMS sensors have an internal battery with a limited service life that may range from five to seven years. Once the battery goes dead, the sensor needs to be replaced. Replacement is usually recommended when the tires are replaced. TPMS sensors also can be fouled by some types of tire sealer products.

A TPMS sensor’s ability to generate a good signal can be checked with a special TPMS tester that energizes the sensor and listens for a radio signal back from the sensor. If a sensor has failed or is not reading accurately, it needs to be replaced. “Universal” aftermarket TPMS sensors are available for a wide variety of applications. Following replacement, a special relearn procedure must be performed so the TPMS system can relearn the position of each sensor correctly.

Making a choice between a remanufactured engine and a rebuilt engine is really a tough one, and you need to assess and weigh out  all the pros and cons of both types of engines to decide.   You need to be aware about the general things that you should consider before you finally say yes to any of these.

Remanufactured Engines vs Rebuilt Engines

A remanufactured engine is remanufactured to the original blueprints and exact specifications, and is tested to original equipment standards.

A rebuilt engine, the repair is done up to the level of failure. This directly means that the engine has been repaired up to the level of failure for which there was a need of rebuilding; but apart from that, components are left intact. The testing procedure of rebuilt engine depends upon the individual rebuilder from whom you are getting the job done.

Crate Engines

Crate Engines are a bit of an inigma for customers, the assumption is that these are remanufactured or rebuilt but that is indeed not the case. A crate engine is a brand new engine available for late model and older cars and trucks that is basically ready to run upon installation. Many crate engines are used for high-performance applications but they are also available for stock applications.

Used Engines

Used engines are just that, engines that have been previously run in another vehicle comparable to the customers and then is transplanted into that vehicle. These engines usually don’t carry a warranty longer than 30 days and can have high mileage on them to begin with.

Many people go with a used engine due to the cost savings but in the long run this can have a damaging affect as the warranty will run out and leave the owner in a financial bind if something goes wrong relativity soon.

During its evolution, the fuel injector has moved from the intake manifold to the combustion chamber. This has made them more precise in dispensing fuel. If this precision is thrown off by restrictions, electrical problems or fuel problems, it can cause driveability issues. Here are 10 signs to look for when you need to replace a fuel injector or it needs service.

1. Restrictions

A restriction of only 8% to 10% in a single fuel injector can lean out the fuel mixture and cause a misfire. When this occurs, unburned oxygen enters the exhaust and makes the O2 sensor read lean. On older multiport systems that fire the injectors simultaneously, the computer compensates by increasing the “on” time of all the injectors, which can create an overly rich fuel condition in the other cylinders.

Direct fuel injectors are more sensitive to restrictions because of the precise amount of fuel they inject into the combustion chamber.

2. Turbo Troubles

In turbocharged engines, dirty injectors can have a dangerous leaning effect that may lead to engine-damaging detonation. When the engine is under boost and at a higher rpm, it needs all the fuel the injectors can deliver. If the injectors are dirty and can’t keep up with the engine’s demands, the fuel mixture will lean out, causing detonation to occur. The leaning out may cause higher than normal exhaust temperatures and turbo failure.

3. Heat Soak

When the engine is shut off, the injectors undergo heat soak. Fuel residue evaporates in the injector nozzles, leaving the waxy olefins behind. Because the engine is off, there is no cooling airflow moving through the ports and no fuel flowing through the injectors to wash it away, so heat bakes the olefins into hard varnish deposits. Over time, these deposits can build up and clog the injectors. Even if a vehicle has low mileage, short drive cycles and increased heat soaks can clog the injector.

Since the formation of these deposits is a normal consequence of engine operation, detergents are added to gasoline to help keep the injectors clean. But if a vehicle is used primarily for short-trip driving, the deposits may build up faster than the detergents can wash them away. On four-cylinder engines, the No. 2 and No. 3 injectors are in the hottest location and tend to clog up faster than the end injectors on cylinders No. 1 and No. 4. The same applies to the injectors in the middle cylinders in six- and eight-cylinder engines. The hotter the location, the more vulnerable the injector is to clogging from heat soaks. Throttle body injectors are less vulnerable to heat soak because of their location high above the intake manifold plenum.

Heat soak can affect direct-injection injectors due to their placement in the head. Even with the higher pressures, the orifices can become clogged over time.

4. Increase or Decrease in Long- and Short-Term Fuel Trims

The fuel calibration curves in the Powertrain Control Module (PCM) are based on OEM dyno testing using a new engine. Fuel pressure is within a specified range for that engine, and the injectors are all clean and new. The PCM’s built-in adaptive fuel control strategies allow it to adjust both short-term and long-term fuel trim to compensate for variances in fuel pressure and fuel delivery to maintain the correct air/fuel ratio — but only within certain limits.

The PCM may not be able to increase injector duration enough to offset the difference if:

• An injector becomes clogged with fuel varnish deposits and fails to deliver its normal dose of fuel when it’s energized, or

• Fuel pressure to the injector drops below specifications because of a weak fuel pump, plugged fuel filter or leaky fuel pressure regulator.

This can leave the air/fuel mixture too lean, causing the cylinder to misfire.

5. Not Enough Resistance

The solenoid at the top of the injector creates a magnetic field that pulls up the injector pintle when the injector is energized. The magnetic field must be strong enough to overcome the spring pressure and fuel pressure above the pintle, otherwise the injector may not open all the way. Shorts, opens or excessive resistance in the injector solenoid can also cause problems.

Typically, the solenoids often short internally when injectors fail, which causes a drop in resistance. If the specification calls for 3 ohms, for example, and an injector measures only 1 ohm, it will pull more current than the other injectors. Too much current flow to an injector may cause the PCM injector driver circuit to shut down, killing any other injectors that also share that same driver circuit. One way to check the injectors is with an ohmmeter.

6. Longer Crank Times

An injector leak will cause the rail to lose pressure while the vehicle is sitting resulting in a longer than normal crank because the rail will need extra time to pressurize.

A normal crank time in a diesel common-rail injection system is usually around three to five seconds. This is how long it will take the common-rail pump to build fuel pressure to the “threshold.” The fuel rail pressure threshold for cranking occurs around 5,000 psi. Normal common-rail systems will operate at 5,000 psi at idle and can reach up to 30,000 psi at wide open throttle.

7. Failed Balance Tests

If you suspect that an injector is clogged or malfunctioning, an injector balance test can isolate the bad injector. Scan tools that can disable injectors can isolate an injector for diagnostics. Engine rpm drop may not be an effective diagnostic method when performing a cylinder balance test where an injector is disabled.

A more effective method is looking at the voltage changes from the O2 sensor. Leaking injectors and some dead injectors can be missed even when an injector is disabled. Other problems with the ignition system and mechanical components also may not show an rpm loss when an injector is turned off. If an injector is good, the voltage from the O2 sensor will drop to or below 100mV. If the problem is a closed or dead injector, the long-term fuel trim may have compensated enough so that the voltage doesn’t change.

Another effective test is to measure the pressure loss in the fuel rail when each injector is fired and pulses for a set period of time. Use an electronic injector pulse tester for this. As each injector is energized, a fuel pressure gauge is observed to monitor the drop in fuel pressure. The electrical connectors to the other injectors are removed, isolating the injector being tested. The difference between the maximum and minimum reading is the pressure drop.

Ideally, each injector should drop the same amount when opened. A variation of 1.5 to 2 psi or more is cause for concern. No pressure drop, or a very low pressure drop, is a sign the orifice or tip is restricted. A higher than normal pressure drop indicates a rich condition that could be caused by a stuck plunger or worn pintle.

8. Misfire Codes

A lean misfire may trigger a misfire code and turn on the check engine light. The code often will be a P0300 random misfire code, or you may find one or more misfire codes for individual cylinders, depending on which injectors are most affected.

9. Vehicle Won’t Start With Full Tank

Major symptoms of contaminated fuel can include cranking no-start, hard starting, stalling, loss of power and poor fuel economy. Because symptoms of fuel contamination generally appear immediately after refueling, the fuel gauge needle pegged on full should always be a diagnostic red flag. Remember to ask if the vehicle has recently been refueled because some drivers just add fuel rather than topping off their tanks.

10. Lack of Maintenance

If an owner has neglected maintenance services like oil changes and filter replacements, chances are the fuel injectors will suffer. For port fuel applications, not changing the oil can result in blowby and a compromised PCV system, which builds up contaminates on the tip of the injector. Not changing the oil in an engine with direct fuel injection can result in a worn fuel pump camshaft lobe.

A damaged cylinder head can be devastating to your engine—and your wallet. And sometimes it's not just your cylinder head that has an issue. It can be an indication of larger engine problems. If the damage is not too extreme, there might be a chance to repair the existing head, but, in many cases it will need to be replaced. For more information on rebuilding vs. remanufacturing a head, read our past blog.

One of the most common causes of cylinder head failure is cracking. This will most likely cause you to need a replacement head, because machine shops aren't always able to repair them very well. This causes the cracks to reoccur soon after a rebuild, putting you in the exact same position, but out the money for the initial repair.

Frequently, cracks appear between the valves, one of the weaker spots on the head, but that's not always the case. The operating conditions play a large role in how the damage occurs on the cylinder head.

CAUSES OF A CRACKED CYLINDER HEAD

The most common cause of cylinder head cracking is overheating. The rapid heating of the engine causes the head to expand and then contract as the engine cools. This puts a large amount of stress on the cylinder head, leading to cracks. Similarly, stressful operating conditions can lead to cracks, along with other engine problems. This is especially true if you have an engine model where your engine block and cylinder head are made of different materials. A common combination is a cast iron block and aluminum head. The two metals expand and contract at different rates, causing cracks in the lighter aluminum head more quickly.

Often, when the head gasket blows, it may be due to the liner "dropping" in the block. This will release the tension holding the head gasket and allow the compression gasses by. It’s also possible that when the compression enters the cooling system, it could displace the coolant, causing the cylinder head to overheat significantly.

Keeping your engine from overheating can help, so it's important to keep a close eye on your coolant levels. Small preventative measures like this can really save you a lot of money down the road.

ISSUES CAUSED BY CYLINDER HEAD CRACKS

A number of issues can arise from a cracked cylinder head. Coolant can enter the cylinders and engine block through the crack. This can contaminate the oil, causing other major engine problems. It could also cause pitting and damage to the engine block. If the coolant enters the cylinder itself, it is often burned off in the exhaust, while damaging the cylinders. If this damage occurs, it's likely that more than just the head and head gasket will need to be replaced to regain a proper seal for combustion and prevent further damage.

Depending on their location, cracks can also cause damage to the valves. This will decrease your engine efficiency, and can also lead to further problems later on.

Cracks in your cylinder head is not something you want to ignore. They obviously aren't going to go away on their own, and more than likely they will lead to further damage on your engine

There are many reasons your check engine light comes on, some simple to fix, some not so simple

Oxygen sensor malfunction.

The oxygen sensor determines the air/fuel mixture that goes into the cylinders for the pistons to push, detonate, and power the engine. The principal of combustion, in this case internal combustion as it applies to your car’s engine, is predicated on oxygen. No air, no boom. No boom, no go. The oxygen sensor analyzes the oxygen flow and fuel mix, and makes adjustments as necessary to make sure the mix isn’t too rich or too lean in the cylinders. The resulting exhaust gases from the combustion in the cylinders pass through the exhaust manifold, where any residual fuel vapor is burned off. The remaining pollutant gases then pass to the catalytic converter, which converts the toxic gases into something a little more environmentally friendly.

If the oxygen sensor malfunctions, a lot of things are affected. Your gas mileage will suffer drastically. The engine just won’t perform as efficiently or powerfully as possible. If you don’t get the oxygen sensor fixed right away, the catalytic converter will be damaged or destroyed. Catalytic converters are expensive, and they are generally just replaced instead of repaired due to their complexity and use of expensive metals such as platinum, palladium, and rhodium. Think $200 oxygen sensor or $2,000 catalytic converter and other expenses. Yay oxygen sensor!

Catalytic converter failure.

Remember that time the check engine light came on and you ignored it for a few weeks, but then you finally got around to having it checked and it was the oxygen sensor that made the light come on? You made sure the mechanic turned off the check engine light, but you ignored the oxygen sensor and didn’t get it fixed for a month. Now the check engine light is back – and instead of $200 for that oxygen sensor you didn’t want to pay, it needs $2,000 or your car won’t run. The catalytic converter has failed, and it’s taking your car with it.

Hey Sparky, pay attention to the light.

The spark plugs create the sparks that make the air/fuel mixture in the cylinders explode. No sparks, no explosions, no internal combustion in the engine means you are going nowhere, or at best, you’re going slowly, noisily, and inefficiently. You might be one of those lucky people that never has to change the spark plugs (whether they need changing or not is another matter – we’re just talking about having to do the actual work) because you know. With the oxygen sensor, replacing spark plugs is cheap. Repairing the damage you get if you don’t replace them is expensive. You’ll probably have to replace the ignition coil, along with the spark plugs, for around $400. Bonus to all of this: the catalytic converter will probably have to be replaced at this point, too. It’s sensitive to spark bad spark plugs. Are you seeing a pattern here?

Mass airflow sensor is on its way out. Act accordingly.

The mass airflow sensor measures the volume of air flowing into the engine and helps determine how much fuel to inject into the engine. Without this, you get all kinds of funky behavior from the engine. It’s hard to start; it hesitates, drags, or jerks, especially at acceleration; the engine hiccups or idle is too fast or too slow. Without this vital component, your vehicle’s emissions output will go up, and your fuel efficiency will go the other direction.

Check engine? Check gas cap.

If the check engine light comes on right after you pull away from the station, it’s a good bet you need to pull over and check that the gas cap is on tight enough. Check it, tighten it, restart the engine and see if the light comes on again. If it doesn’t, you just fixed the problem!

If the cap is on nice and tight, and the check engine light comes on again, then there is something else wrong. It is possible that the gas cap is loose and won’t tighten anymore, or has a leak due to a worn out seal or a crack. In these cases, it’s a good idea to get a new gas cap and see if that fixes the problem. If the check engine light doesn’t come on after you replace the fuel cap, you’ve just saved yourself time, money, and many sleepless nights.

Of course, if you pull over to investigate and the gas cap is not on at all – as in missing – then you probably should go back to the gas station and look for it. If you can’t find it, a new cap is in your immediate future and will most likely make the check engine light go away.

Engine blocks are designed to handle the rigors of ordinary driving and then some. However, while rare, failure does occur. Cracks in engine blocks usually require replacement (either with a crate engine, a rebuilt engine, salvage engine or remanufactured engine). Repairs can be done in some instances, but it’s not always possible. What causes engine blocks to crack, though? Here are four culprits.

THE ONLY REAL REASON FOR CRACKED ENGINE BLOCKS

While there are many underlying causes of cracked engine blocks, they almost all involve excess heat. Engine coolant is what’s supposed to keep the overall engine within operating temperature, but extreme overheating changes things. In these instances, the coolant isn’t enough to keep all of the block cool (because it can only cool the immediate area through which it runs). The overheated portions expand while the cooler areas don’t. The result is stress on the block and then an engine-killing crack. So, what causes overheating?

Low coolant is the primary cause of overheating. If your customer runs their engine with the low coolant light on, they should expect to suffer some very serious problems. Whether the situation was caused by failure to maintain their coolant properly or their radiator failed, the situation can be very serious if not caught in time, especially in used car engines for sale.

Water pump failure is another thing that can cause a cracked block. Even if the coolant level is fine, without a functional water pump, the coolant can’t flow through the system and cool as it is designed to do. This can lead to severe overheating and a cracked block.

Casting failure is the third cause of engine block cracks. While rare, it does happen. During the injection molding process, a shift in the mold’s sand can cause the block’s metal to be thinner than necessary in certain areas. Over time and with the application of heat (expansion and contraction), these thin areas can crack.

Overheating due to overpowering is another cause of cracked engine blocks. Adding a supercharger or turbocharger to an engine not designed for one can create a situation in which the engine has more power (and generates more heat) than it can handle. This creates extra flexing and expansion in the block (because the coolant can’t handle the amount of heat generated by the added power), resulting in a cracked block.

In most instances, replacing an engine with a cracked engine block is the best solution, particularly if your customer is interested in a salvage engine or a rebuilt engine (both of which are more economical than crate or remanufactured engines).

Chevy’s renowned for the company’s small block engines, but that doesn’t mean they’re indestructible. Eventually, you’re going to have to replace your engine if you want to keep that car or truck on the road. There’s good news, though. Chevy Silverado, Impala, Blazer, Camaro and S10 owners will find that replacing their engines is easier with a few important tips.

Front or Rear Wheel Drive?

The Chevy Silverado, Blazer, S10 and Camaro are all rear-wheel drive vehicles, while the Impala is a front-wheel drive car (at least the modern model is). For rear-wheel drive vehicles, it’s usually easiest to replace the engine if you take the drive shaft loose from the rear of the transmission first. This lets you loosen the transmission if necessary and gain a bit of extra space.

Front-Wheel Drive

Unlike the Silverado, S10, Blazer and Camaro, owners of a Chevy Impala need to disassemble most of the front steering and suspension system in order to remove the CV axles from the transmission. While you won’t be pulling the transmission during engine replacement, it’s easier if you have a little more play in the transmission so you can ensure it’s out of the way when you drop the engine.

Don’t Forget the Components

An engine replacement generally doesn’t come with anything more than the engine itself. In many cases, your crate engine, rebuilt engine or used engine may not even come with an oil pan. What that means is that you’ll have to reuse the old components from the original engine in in your Blazer, S10, Camaro, Silverado or Impala. To ensure that you know exactly what components you’ll need, it’s highly recommended that you not discard any parts from your original engine before the replacement arrives.

Once your replacement is there, you know exactly what parts you’ll need to reuse. On average, you’ll need to reuse the starter, alternator, thermostat, valve cover and all the belts. Double-check that the oil pan doesn’t need to be reused. You should also make sure that you have replacement gaskets for the valve cover, oil pan, thermostat and any other components that need to be reused.

You should not have to reuse components like the timing belt or water pump – these are often included with your Chevy replacement engine. However, it always pays to verify before going through with the replacement just to be on the safe side.

Chevy, perhaps more so than most other automakers, has a long history of producing powerful engines. The Chevy small block is legendary in the automotive industry for some very good reasons. Of course, the company has far more to offer than the small block and there are some very popular Chevy engines out there. Here’s a look at some of the most popular options Chevrolet has put out. To keep this discussion within reason, we’ll limit these to those produced since the 1980s through today.

The LT5

The LT5 might not be your first thought for most popular Chevy engines, thanks to the fact that it actually had less overall power than the model preceding it, but it still rates. Actually, the fact that it varied from the traditional Chevy small block footprint at the time but still produced 375 HP is a mark in its favor, and it defined the 1989 Corvette.

The LT1

The LT1 debuted in 1994 and offered a minimum of 300 HP (with a max of 350 HP during its lifespan). That means it provided 75 HP less than the LT5 before it. However, what really made this such a popular engine was the power for price – it was affordable, which put 300+ HP capabilities within reach for more people.

The LS7

With more than 500 HP, the LS7 is a world-class performer and one of the most recognizably popular Chevy engines on the market. Of course, the fact that it was basically the same engine as the Chevy racing team used in Le Mans didn’t hurt its popularity either.

The LS9

When it comes to powerhouses, few consumer engines can compare with the LS9 and its 556-638 HP. The engine debuted in 2009 and remains the most expensive production engine for Chevy’s Corvette. That price point didn’t hamper its popularity (if you could actually afford to pay for it, of course), and it remains one of the most popular engines the manufacturer has produced to date.

The success of Chevy engines is based largely on the quality of its small block design. However, the automaker has deviated from that design from time to time and still managed to produce big results. The automaker remains the most recognizable American automaker producing high performance engines, even more so than Ford with its range of V8 engines used in the Mustang.

Ford makes some of the most reliable engines in the world (as evidenced by the multiple awards the company has won in recent years), but eventually, engine replacement will be a necessity. Whether the vehicle in question is an F-150, a Ford Ranger, Explorer, Mustang or Expedition, the following tips will help ensure a smooth removal and installation process.

Lift the Vehicle

Whether you’re working on an F-150, Mustang, Ranger, Expedition or Explorer, the first thing to do is put the vehicle on a lift. You can use jack stands and an engine hoist if necessary, but it’s far easier to remove the old engine from the vehicle on a full lift.

Open the Hood

Once you’ve got the vehicle in the air a few inches (just enough to get the wheels off the floor), open the hood, then disconnect and remove the battery. Because the Ford Explorer, F-150, Mustang, Ranger and Expedition are all rear-wheel drive vehicles, you’ll have an easier time of things than if you were working on a front-wheel drive car.

Raise the vehicle and remove the two front wheels. Remove the mounting bolts holding the engine to the transmission. Lower the truck so you can reach under the hood. Take off the engine shroud if your model has one, and unplug all the electronics. Put a support under the engine and transmission, and then remove the engine mounts. You’ll also need to take care of the radiator, hoses and thermostat.

Pulling the Engine

In most instances, it’s necessary to pull the engine from above, although you can pull it from below if you have an engine jack and enough room to do the job. Remove the engine slowly and keep an eye out for any wires that haven’t been unplugged. If you meet resistance, double-check that there wasn’t a mounting bolt left in place as well.

Once you have the engine out of the truck, you’ll need to remove all the components that aren’t included in your replacement engine. In most instances, Ford F-150, Ranger, Mustang, Expedition and Explorer replacement engines come with just the basics (you get the engine itself and nothing much else). Remove the thermostat, alternator, starter and other components from the damaged engine, and install them on the replacement engine. Finally, you’ll need to reinstall the replacement engine in the reverse order of the above. In most instances, pulling the engine from your F-150, Ranger, Expedition, Mustang or Explorer should take about a day’s worth of work, but it might be longer depending on your situation.

Generally speaking, the various fluids used in an automobile’s engine should stay within their perspective systems. However, in real life, that’s not always the case. There are numerous ways that leaks can start, and given the number of fluid-based systems in the average automotive engine, there are lots of leaks possible. However, one that you’ll want to watch for very carefully is coolant/water mixing with the engine oil, commonplace when purchasing cheap engines online.

What’s the Issue?

If there’s coolant or water mixing with the engine oil, it’s a bad sign. Most commonly, it’s a sign that there’s a blown head gasket. However, other problems can cause this too, including a cracked block and compression issues. The problem here (aside from the obvious leak and potential for damage) is that antifreeze alters the properties of engine oil. It actually thickens the oil, making it harder to flow through oil channels and lubricate the engine.

How to Detect Coolant in the Oil

So, how do you detect coolant or water in the engine oil? The gold-standard test is to remove the oil filler cap and look in the filler neck/under the cap for white or light brown buildup. This CAN indicate coolant leaking into the engine oil, but it’s not a guaranteed accurate method. The problem here is that condensation can build up within an engine and cause discoloration around the filler cap. This is particularly true with vehicles that are only driven short distances (daily drivers or cars that are only driven rarely). In order to dispel condensate buildup, you have to heat the engine to a certain point and then maintain it.

A better method for detecting coolant contaminating engine oil is to look for “milk chocolate” on the oil dipstick. When coolant mixes with engine oil, it creates a light brown liquid that looks an awful lot like chocolate milk. If you notice this on the dipstick, there’s a problem and you need to diagnose it. Finding the leak can be tough to do, though, unless it’s something pretty obvious like a cracked block. Check for head gasket leaks, and if necessary, do a leak down test on each cylinder.

In most cases, replacing the head gasket or repairing the compression problem (coupled with a thorough cleaning of the buildup within the engine) will do the trick, but that’s not always the case.

Worst Case Scenario

In the worst-case scenario, you’ll need to talk to your customer about engine replacement. A crate enginewould be ideal, but remanufactured and even salvage engines can be good options, particularly if your customer has a limited budget.

Engine overheating, while common, can be terribly destructive. If your customer manages to exceed the maximum operating temperature of their engine for more than a very short time, it can cause complete engine destruction. Of course, total lockup isn’t that common, but there are a number of different things that can happen when an engine’s temperature soars, commonplace among cheap engines auctioned off on the internet. What causes engine overheating and what repercussions might your customer suffer?

Damage to the Head Gasket

One of the first things that overheating can do to your customer’s car is crack the head gasket. As the engine’s temperature soars, the metal expands. The more expansion there is, the more pressure the engine puts on the head gasket. Eventually, the gasket will crack. A cracked head gasket isn’t necessarily a death knell for the engine, but it can be very problematic. It can allow antifreeze into the oil and vice versa, and can also cause very serious oil leaks.

Cracked or Warped Cylinder Head

In extreme cases of overheating, you’ll find that the damage goes deeper than just a blown head gasket. It can actually warp or even crack a cylinder head. To find out if this is the case, you’ll need to do a compression test on the engine. A pressure test on the cooling system will also help determine if there was damage to the head.

Causes of Overheating

The number one cause of engine overheating is driver negligence. The world is rife with stories of customers with leaking radiators who managed to keep things running by adding water on short trips. The “I’ll get it soon” mentality has killed more engines than anything else. That applies to everything from not replacing a radiator with a known leak to not checking the coolant level regularly, not inspecting the cooling system hoses and failing to do a coolant change when necessary.

However, there are some causes that are outside the customer’s control. For instance, thermostats that stick shut are not anything that your customer can prevent, and are both common and detrimental to engine health. Others include failed or leaking water pumps, failed cooling fans and fan motors and more.

Overheating is deadly to an engine. If your customer has brought in a car for engine overheating, be thorough in your diagnostics. Make sure to address both the repercussions of overheating (potential warped head, for instance), as well as the underlying cause of the problem.

Used engines offer affordable replacement options when a car’s original engine goes south. However, they’re not perfect, especially the many used engines for sale listed on auctions. Sometimes, you might experience problems with a used engine – they are used, after all. And no amount of testing by the supplier is going to be able to identify every single problem that might arise. One issue you might struggle with is spark knock after replacing a car’s engine. Here’s a few handy tips to help you diagnose the problem of a spark knock on a used engine.

Look for a Simple Answer

Spark knock on a used engine can be caused by a variety of different things, ranging from the easily fixable to those requiring a lot of time and effort on your part. Start with the simplest – the EGR valve. The EGR valve (and the EGR system as a whole) is the most common culprit when there’s a problem with spark (fire). The exhaust gas recirculation valve (EGR) is part of the emissions system, but if it gets gummed up, sticks closed or has a gasket failure, some strange things can happen, including spark knock. Test the valve and see if it’s malfunctioning. If so, replace it and clean the system (make sure you replace the valve gasket as well), and you should be good to go.

Fuel Problems

Spark knock can also be caused by fuel issues. Most notably, if your customer is driving a higher performance vehicle but only putting in low-octane fuel, spark knock can result. The problem here is the octane in the fuel. Another fuel-related issue is if the engine is running “lean”. That is, it’s getting too much air and not enough fuel for combustion. This is the opposite of running rich, and will require that you dig into the fuel injection system to determine the cause (a clogged injector is the primary problem, but there are other issues, including leaking fuel rails).

Carbon, Carbon, Carbon

Carbon deposits are the bane of good engine operation. While carbon deposits are more common in higher mileage vehicles, they can show up in those with moderate mileage as well. Carbon that builds up on the piston crowns and within the combustion chambers will cause spark knock. The best option here is to clean the carbon off thoroughly (this is generally a job that must be done by hand, though a “top end engine cleaner” can also work if the deposits are not severe).

Finally, spark knock on a used engine isn’t caused by the need for a new timing belt, though it can be caused if the belt slips and the cam jumps ahead by a tooth.

It’s normal to see a car’s exhaust when it’s first cranked up in the morning. Drivers will also see the exhaust if it’s particularly cold outside. However, what they’re seeing is mostly water vapor (it’s white). They’re not really seeing smoke. That changes if you can see your customer’s exhaust on warm days or after the engine has warmed up to its normal operating temperature. If the exhaust looks bluish and smoky, rather than being mostly water vapor, what you’re seeing is a sign that there is an engine burning oil situation, which is a bad thing.

Making a Diagnosis

Car engines can burn oil for any number of different reasons. However, none of them are good, especially in cheap engines newly purchased. At best, it’s a sign that there’s wear and tear, and that the engine oil level will drop significantly between oil changes, which can cause serious damage if your customer isn’t paying attention. Making the right diagnosis here is important.

The first place to start is with the EGR valve. As you should know, the EGR system is the primary culprit for a number of problems, including spark knock. However, it’s an important part of the vehicle’s emissions system, and needs to be checked for operation. If the problem isn’t here, though, you’ll need to dig deeper.

The car engine’s rings and seals are the most likely culprits if the EGR valve is working normally. You’ll see this particularly with older model engines. To confirm that this is the problem, you’ll have to test the engine’s compression. Low compression indicates that the rings and seals are worn out and not working properly.

When you inform your customer that they need to replace both rings and seals, be prepared for resistance. Most customers know that an engine can be run for quite some time while burning oil without replacing rings or seals. The real danger here is that they’ll run it too long without adding oil and lock it up. It’s best to convenience them that they need a ring job, or you can start pricing replacement engines if they would prefer (or if the problem is severe).

If the problem is serious and there’s been substantial damage to the engine over time, it might be best just to recommend a replacement engine (rebuilt, remanufactured or used engines can all work). Make sure to quote both the price and the time it will take to complete the replacement.