Operation

The water pump (also called a coolant pump) is driven by one of two methods.

• Crankshaft belt
• Camshaft

Coolant recirculates from the radiator to the engine and back to the radiator. Low-temperature coolant leaves the radiator by the bottom outlet. It is pumped into the warm engine block, where it picks up some heat. From the block, the warm coolant flows to the hot cylinder head, where it picks up more heat.

• NOTE: Some engines use reverse cooling. This means that the coolant flows from the radiator to the cylinder head(s) before flowing to the engine block.

A demonstration engine running on a stand showing the amount of coolant flow that actually occurs through the cooling system.

Frequently Asked Quesiton: How much Coolant Can a Water Pump Move?

A typical water pump can move a maximum of about 7,500 gallons (28,000 liters) of coolant per hour, or recirculate the coolant in the engine over 20 times per minute. This means that a water pump could be used to empty a typical private swimming pool in an hour! The slower the engine speed, the less power is consumed by the water pump. However, even at 35 mph (56 km/h), the typical water pump still moves about 2,000 gallons (7,500 liters) per hour or 0.5 gallon (2 liters) per second!

Water pumps are not positive displacement pumps. The water pump is a centrifugal pump that can move a large volume of coolant without increasing the pressure of the coolant. The pump pulls coolant in at the center of the impeller. Centrifugal force throws the coolant outward so that it is discharged at the impeller tips.

As engine speeds increase, more heat is produced by the engine and more cooling capacity is required. The pump impeller speed increases as the engine speed increases to provide extra coolant flow at the very time it is needed.

Coolant flow through the impeller and scroll of a coolant pump for a V-type engine

Coolant leaving the pump impeller is fed through a scroll. The scroll is a smoothly curved passage that changes the fluid flow direction with minimum loss in velocity. The scroll is connected to the front of the engine so as to direct the coolant into the engine block. On V-type engines, two outlets are often used, one for each cylinder bank. Occasionally, diverters are necessary in the water pump scroll to equalize coolant flow between the cylinder banks of a V-type engine in order to equalize the cooling.

Water Pump Service

A worn impeller on a water pump can reduce the amount of coolant flow through the engine.

If the seal of the water pump fails, coolant will leak out of the weep hole. The hole allows coolant to escape without getting trapped and forced into the water pump bearing assembly.

The hole allows coolant to escape without getting trapped and forced into the water pump bearing assembly.

If the bearing is defective, the pump will usually be noisy and will have to be replaced. Before replacing a water pump that has failed because of a loose or noisy bearing, check all of the following:

1. Drive belt tension
2. Bent fan
3. Fan for balance

If the water pump drive belt is too tight, excessive force may be exerted against the pump bearing. If the cooling fan is bent or out of balance, the resulting vibration can damage the water pump bearing.

Tech Tip: Release the Belt Tension before Checking a Water Pump

The technician should release water pump belt tension before checking for water pump bearing looseness. To test a water pump bearing, it is normal to check the fan for movement; however, if the drive belt is tight, any looseness in the bearing will not be felt.

Next Steps towards ASE Certification

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Purpose and Function

Excess pressure usually forces some coolant from the system through an overflow. Most cooling systems connect the overflow to a plastic reservoir to hold excess coolant while the system is hot.

When the system cools, the pressure in the cooling system is reduced and a partial vacuum forms. This vacuum pulls the coolant from the plastic container back into the cooling system, keeping the system full. Because of this action, the system is called a coolant recovery system. A vacuum valve allows coolant to reenter the system as the system cools so that the radiator parts will not collapse under the partial vacuum.

The level in the coolant recovery system raises and lowers with engine temperature.

Surge Tank

Some vehicles use a surge tank, which is located at the highest level of the cooling system and holds about 1 quart (1 liter) of coolant. A hose attaches to the bottom of the surge tank to the inlet side of the water pump. A smaller bleed hose attaches to the side of the surge tank to the highest point of the radiator. The bleed line allows some coolant circulation through the surge tank, and air in the system will rise below the radiator cap and be forced from the system if the pressure in the system exceeds the rating of the radiator cap.

Some vehicles use a surge tank, which is located at the highest level of the cooling system, with a radiator cap.

Real World Fix: The Collapsed Radiator Hose Story

An automotive student asked the automotive instructor what brand of radiator hose is the best. Not knowing exactly what to say, the instructor asked if there was a problem with the brand hose used. The student had tried three brands and all of them collapsed when the engine cooled. The instructor then explained that the vehicle needed a new pressure cap and not a new upper radiator hose. The student thought that because the lower hose did not collapse that the problem had to be a fault with the hose. The instructor then explained that the lower radiator hose has a spring inside to keep the lower hose from collapsing due to the lower pressure created at the inlet to the water pump. The radiator cap was replaced and the upper radiator hose did not collapse when the engine cooled.

Next Steps towards ASE Certification

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Types of Radiator Cores

The two types of radiator cores in common use in most vehicles are:

• Serpentine fin core
• Plate fin core

In each of these types, the coolant flows through oval-shaped core tubes. Heat is transferred through the tube wall and soldered joint to cooling fins. The fins are exposed to the air that flows through the radiator, which removes heat from the radiator and carries it away.

The tubes and fins of the radiator core.

Since the 1980s, most radiators have been made from aluminum with nylon-reinforced plastic side tanks. These materials are corrosion resistant, have good heat transferability, and are easily formed.

Core tubes are made from 0.0045 to 0.012 in. (0.1 to 0.3 mm) sheet brass or aluminum, using the thinnest possible materials for each application. The metal is rolled into round tubes and the joints are sealed with a locking seam.

The two basic designs of radiators include:

1. Down-flow radiators. This design was used mostly in older vehicles, where the coolant entered the radiator at the top and flowed downward, exiting the radiator at the bottom.
2. Cross-flow radiators. Most radiators use a cross-flow design, where the coolant flows from one side of the radiator to the opposite side.

A radiator may be either a down-flow or a cross-flow type.

How Radiators Work

The main limitation of heat transfer in a cooling system is in the transfer from the radiator to the air. Heat transfers from the water to the fins as much as seven times faster than heat transfers from the fins to the air, assuming equal surface exposure. The radiator must be capable of removing an amount of heat energy approximately equal to the heat energy of the power produced by the engine. Each horsepower is equivalent to 42 BTUs (10,800 calories) per minute. As the engine power is increased, the heat-removing requirement of the cooling system is also increased.

With a given frontal area, radiator capacity may be increased by increasing the core thickness, packing more material into the same volume, or both. The radiator capacity may also be increased by placing a shroud around the fan so that more air will be pulled through the radiator.

• NOTE: The lower air dam in the front of the vehicle is used to help direct the air through the radiator. If this air dam is broken or missing, the engine may overheat, especially during highway driving due to the reduced airflow through the radiator.

When a transmission oil cooler is used in the radiator, it is placed in the outlet tank, where the coolant has the lowest temperature.

Many vehicles equipped with an automatic transmission use a transmission fluid cooler installed in one of the radiator tanks.

Pressure Caps

Operation

On most radiators the filler neck is fitted with a pressure cap. The cap has a spring-loaded valve that closes the cooling system vent. This causes cooling pressure to build up to the pressure setting of the cap. At this point, the valve will release the excess pressure to prevent system damage. Engine cooling systems are pressurized to raise the boiling temperature of the coolant.

• The boiling temperature will increase by approximately 3°F (1.6°C) for each pound of increase in pressure.
• At sea level, water will boil at 212°F (100°C). With a 15 PSI (100 kPa) pressure cap, water will boil at 257°F (125°C), which is a maximum operating temperature for an engine.

Functions

The specified coolant system temperature serves two functions.

1. It allows the engine to run at an efficient temperature, close to 200°F (93°C), with no danger of boiling the coolant.
2. The higher the coolant temperature, the more heat the cooling system can transfer. The heat transferred by the cooling system is proportional to the temperature difference between the coolant and the outside air. This characteristic has led to the design of small, high-pressure radiators that are capable of handling large quantities of heat. For proper cooling, the system must have the right pressure cap correctly installed.

A vacuum valve is part of the pressure cap and is used to allow coolant to flow back into the radiator when the coolant cools down and contracts.

• NOTE: The proper operation of the pressure cap is especially important at high altitudes. The boiling point of water is lowered by about 1°F for every 550 ft increase in altitude. Therefore, in Denver, Colorado (altitude 5,280 ft), the boiling point of water is about 202°F, and at the top of Pike’s Peak in Colorado (14,110 ft) water boils at 186°F.

Metric Radiator Caps

According to the SAE Handbook, all radiator caps must indicate their nominal (normal) pressure rating. Most original equipment radiator caps are rated at about 14 to 16 PSI (97 to 110 kPa).

The pressure valve maintains the system pressure and allows excess pressure to vent. The vacuum valve allows coolant to return to the system from the recovery tank.

However, many vehicles manufactured in Japan or Europe use radiator pressure indicated in a unit called a bar. One bar is the pressure of the atmosphere at sea level, or about 14.7 PSI. The conversions can be used when replacing a radiator cap, to make certain it matches the pressure rating of the original.

• NOTE: Many radiator repair shops use a 7 PSI (0.5 bar) radiator cap on a repaired radiator. A 7 PSI cap can still provide boil protection of 21°F (3°F x 7 PSI = 21°F) above the boiling point of the coolant. For example, if the boiling point of the antifreeze coolant is 223°F, then 21°F is added for the pressure cap, and boilover will not occur until about 244°F (223°F + 21°F = 244°F). Even though this lower pressure radiator cap provides some protection and will also help protect the radiator repair, the coolant can still boil before the “hot” dash warning light comes on and, therefore, should not be used. In addition, the lower pressure in the cooling system could cause cavitation to occur and damage the water pump. For best results, always follow the vehicle manufacturer’s recommended radiator cap.

Working Better Under Pressure

A problem that sometimes occurs with a high-pressure cooling system involves the water pump. For the pump to function, the inlet side of the pump must have a lower pressure than its outlet side. If inlet pressure is lowered too much, the coolant at the pump inlet can boil, producing vapor. The pump will then spin the coolant vapors and not pump coolant. This condition is called pump cavitation. Therefore, a radiator cap could be the cause of an overheating problem. A pump will not pump enough coolant if not kept under the proper pressure for preventing vaporization of the coolant.

Next Steps towards ASE Certification

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Two important things about a thermostat include :

1. An overheating engine may result from a faulty thermostat.
2. An engine that does not get warm enough always indicates a faulty thermostat.

To replace the thermostat, coolant will have to be drained from the radiator drain petcock to lower the coolant level below the thermostat. It is not necessary to completely drain the system. The hose should be removed from the thermostat housing neck and then the housing removed to expose the thermostat.

Failure to set the thermostat into the recessed groove will cause the housing to become tilted when tightened.

The gasket flanges of the engine and thermostat housing should be cleaned, and the gasket surface of the housing must be flat. The thermostat should be placed in the engine with the sensing pellet toward the engine. Make sure that the thermostat position is correct, and install the thermostat housing with a new gasket or O-ring.

CAUTION: Failure to set the thermostat into the recessed groove will cause the housing to become tilted when tightened. If this happens and the housing bolts are tightened, the housing will usually crack, creating a leak.
The upper hose should then be installed and the system refilled. Install the correct size of radiator hose clamp.

Next Steps towards ASE Certification

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Luckily within the State of Wyoming, any good car technician is not required to get a license to service cars and trucks!

But nevertheless, simply because there’s no structured or national requirement does not necessarily mean all auto mechanics are similarly competent for a role in an automotive mechanic shop.

Within Wyoming, automotive technicians who match the following qualifications are a great deal more apt to obtain a career in an automobile repair center compared to job hopefuls that do not fulfill a majority of these minimal requirements:

• Automotive Service Excellence (ASE) Certification (Master Mechanic certification preferred)
• Wyoming work experience in one of the following areas:
• Repair Technician – 1, 2, or 3 years
• Collision Damage Estimator – 2 years
• On-the-job training from local automotive dealers
• 2 years prior experience in the automotive repair industry
• Formal education training such as:
• Vocational training
• Tech school training and classes
• Community college classes

Incomes and Salaries for Automotive Technicians in Wyoming

Extra Qualifications

In order to make yourself a great deal more marketable to potential business employers, the majority of auto mechanics will discover that their own career opportunities improve if they’re able to attain additional accreditations and education:

Automobile Service Excellence (ASE) Certification in Wyoming

A large number of auto mechanics choose to obtain valuable certification from the National Institute for Automotive Service Excellence (ASE) (www.ase.com). ASE is an independent, non-profit association that enhances the the effectiveness of automotive repairs and auto service by certifying and testing auto repair and service industry experts. ASE Certification is usually a crucial element of a mechanic’s experience and resume, and can help showcase knowledge and make mechanics far more marketable to potential employers. Just be sure you invest some time to study for the assessments by using our absolutely free examination tools and questions. Car technicians along with other service specialists that would like to get ASE certification may take a few of ASE’s 40 examinations. Upon passing these job-related proficiency assessments, the mechanic will become ASE certified in any one of the following subjects: Automobile, truck equipment, collision repair, and much more.

Refrigerant Certification in Wyoming

The United States Environmental Protection Agency (EPA) requires all vehicle service technicians that work with or purchase refrigerants to secure licensing in proper handling of refrigerants. Right now there is no structured test preparation mandated, but many labor unions, trade schools, and employer associations offer lessons and seminars for examination preparation. Further details about this official certification can be found at the official EPA site.

ASE Student Certification in Wyoming

ASE Student Certification can assist you move on the right road for developing a professional career as a good service skilled professional in the automotive industry. Unlike the full ASE accreditation, there are no work experience requirements for student certification. Any student simply just has to successfully pass one or more of the student certification tests. As soon as the student has skillfully completed one or more assessments, the teachers prints the certification and has it approved by the school principal and it is awarded to the individual. The student accreditation is valid for two years after the assessment date.

Personal Qualities for Wyoming Certified Auto Mechanics

Eagle Eyes: Motor vehicle challenges can often times be caused by disregarded misalignments or issues which can be detected by a very detailed auto mechanic. The nature of an car or truck technician is to go over every last plausible challenge with very good depth when reaching a diagnosis or repair.

Commitment to Service: Automotive service techs work with customers on a regular basis, and the greatest specialists establish special personalised relationships with their customers that keep them wanting future Assistance. Quite a few techs take too lightly this part of the Wyoming vehicle maintenance marketplace.

Troubleshooting skills: A vital capability of automotive specialists certainly is the competency to troubleshoot engine, physical, and wear-related problems with motor vehicles and also other sophisticated systems. The capability to discover and correct problems frequently comes with on-the-job experience and training in a maintenance shop.

Typical Pay in Wyoming by City:

Next Steps towards ASE Certification

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The good news is within the State of Vermont, any automotive service technician is not required to have a license to service cars!

But nevertheless, although there isn’t a standard or widespread prerequisite certainly does not mean virtually all mechanics are equally proficient for a career in an automotive mechanic shop.

Operating in Vermont, auto mechanics that fulfill the following criteria are much more likely to get a position in an motor vehicle mechanic shop in comparison with job seekers that do not meet these minimum criteria:

• Automotive Service Excellence (ASE) Certification (Master Mechanic certification preferred)
• Vermont work experience in one of the following areas:
• Parts Specialist – 2 years
• Collision Damage Estimator – 2 years
• On-the-job training from local automotive dealers
• Plus: Any car manufacturer certifications (e.g. General Motors, Chrysler, Mercedes, BMW, etc.)
• Automotive Repair Classroom Training:
• Collision repair training
• Repair Technology training courses (including diagnostic software)

Salaries and Incomes for Auto Mechanics in Vermont

Some Additional Experience

In order to make oneself even more marketable to future mechanic shops, many automotive technicians will quickly realize that their career opportunities increase if they are able to accomplish additional accreditations and education:

Automobile Service Excellence (ASE) Certification in Vermont

Many automotive mechanics decide to obtain special recognition from the National Institute for Automotive Service Excellence (ASE) (www.ase.com). ASE is an third party, non-profit organization that improves the quality of motor vehicle repair and servicing by certifying and testing maintenance and service professionals. ASE Certification is definitely a fundamental aspect of an auto technician’s experience and credentials, and definately will help exhibit competencies and help to make mechanics even more marketable to potential auto repair shops. Just ensure that you devote some time to study for the exams utilizing our free assessment tools and quiz questions. Automotive specialists and also other service industry experts that want to get ASE certification are able to take a few of ASE’s 40 exams. Upon passing these job-related capability tests, the specialist becomes ASE certified in any of the following areas: medium/heavy truck, truck equipment, school bus, and more.

Refrigerant Certification in Vermont

The United States Environmental Protection Agency (EPA) requires all vehicle technicians that work with or acquire refrigerants to obtain certification in correct handling of refrigerants. There is not a formal exam preparation mandated, but a large number of unions, technical schools, and employer groups offer classes and workshops for examination preparation. Further information regarding this qualification can be obtained on the official EPA website.

ASE Student Certification in Vermont

ASE Student Certification will let you move on the ideal course for building a professional career as an effective service skilled professional within the automotive industry. Compared with the full ASE certification, there isn’t any industry experience prerequisites for student certification. The applicant simply needs to pass one or more of the student certification tests. As soon as the trainee has skillfully finished one of these tests, the faculty prints the certification and has it approved by the school principal and it is presented to the individual. The student accreditation is valid for 2 years after the examination date.

Desirable Qualities for Vermont Professional Auto Technicians

Eagle Eyes: Vehicular problems can frequently times result from overlooked details or circumstances that may be identified by a really detail-oriented auto technician. The nature of an car or truck service professional is to look over each and every plausible challenge with very good detail when deciding on a diagnosis or repair service.

Service Excellence: car service techs work closely with clients regularly, and the greatest technicians develop close individualized working relationships with their customers that keep them wanting potential future Assistance. A large number of specialists undervalue this aspect of the Vermont vehicle service marketplace.

Troubleshooting skills: A fundamental proficiency of automobile professionals is the skill to diagnose electrical, technical, and functional problems with cars and also other sophisticated systems. The ability to recognize and fix complications often comes along with on-the-job experience and training in a repair and maintenance shop.

Ranges of Pay in Vermont by City:

Next Steps towards ASE Certification

Now that you’re familiar with all of the ASE Certification requirements in Vermont, try out our free Automotive Service Excellence Tests to see how much you know!

The good thing is within the State of North Dakota, any good auto technician is not mandated to get a license to diagnose and fix automobiles!

Nevertheless, even though there’s no formal or universal qualification does not imply most auto mechanics are equally eligible for a job in an automobile repair center.

In North Dakota, repair technicians that fulfill the following criteria are significantly more likely to obtain a role in an motor vehicle repair shop when compared with applicants that do not meet a majority of these minimal prerequisites:

• Automotive Service Excellence (ASE) Certification (Master Mechanic certification preferred)
• North Dakota work experience in one of the following areas:
• Repair Technician – 1, 2, or 3 years
• Service Consultant – 2 years
• On-the-job training from local automotive dealers
• 2 years prior experience in the automotive repair industry
• Formal education training such as:
• Trade-school courses
• Tech school training and classes
• Community college classes

Incomes and Salaries for Motor vehicle Specialists in North Dakota

Various other Recommendations

Making yourself substantially more marketable to potential mechanic shops, the majority of auto mechanics will quickly realize that their own career prospects improve if they can accomplish extra qualifications and training:

Automobile Service Excellence (ASE) Certification in North Dakota

A large number of automotive mechanics elect to acquire special certification from the National Institute for Automotive Service Excellence (ASE) (www.ase.com). ASE is an third party, non-profit organization that works to improve quality of automobile repair and services by certifying and testing repair work and auto service specialists. ASE Certification is usually a vital aspect of an auto technician’s experience and credentials, and definately will help showcase competencies and make applicants more marketable to potential auto repair shops. Simply make certain you devote some time to review for the exams utilizing our free testing resources and test questions. Car technicians along with other service professionals that would like to get ASE certification could take any of ASE’s 40 assessments. After completing these job-related competency examinations, the specialist will become ASE certified in several of the following areas: medium/heavy truck, truck equipment, school bus, and much more.

Refrigerant Licensing in North Dakota

The U . S . Environmental Protection Agency (EPA) mandates all automotive specialists that work with or purchase refrigerants to acquire licensing in correct handling of refrigerants. Currently there is no formal examination preparation mandated, but a large number of unions, trade schools, and company organizations offer instructional classes and workshops for test preparation. Further information about this qualification can be read at the official EPA site.

ASE Student Certification in North Dakota

ASE Student Certification will let you proceed on the correct road for establishing a professional career as a good service specialist in the car industry. Compared with the actual ASE official certifications, there are not any mechanic experience requirements for student certification. Any student simply would need to complete one or more of the student certification tests. When the student has proficiently achieved one or two assessments, the teachers prints the certificate and has it approved by the school principal and it is given to the student. The student accreditation is valid for 2 years from the assessment date.

Individual Characteristics for North Dakota Professional Mechanics

Very Detailed: Motor vehicle difficulties can frequently times result from missed problems or issues that can be caught by a extremely detailed auto technician. The nature of an motor vehicle technician is to check out every possible problem with fantastic detail when producing a prognosis or repair service.

Customer Service Experience: car service techs work closely with customers everyday, and the most successful auto mechanics develop close individualized relationships with their customers that keep them coming back for long term future Assistance. Quite a few specialists underrate this part of the North Dakota automotive repair market place.

Diagnostic Skills: A crucial proficiency of automotive professionals is definitely the ability to troubleshoot electrical, physical, and functional complications with cars and trucks along with other complicated systems. The ability to recognise and correct complications usually comes with hands-on experience and training in a repair and maintenance shop.

Common Incomes in North Dakota by City:

Next Steps towards ASE Certification

Now that you’re familiar with all of the ASE Certification requirements in North Dakota, try out our free Automotive Service Excellence Tests to see how much you know!

Cooling System

Purpose and Function

Satisfactory cooling system operation depends on the design and operating conditions of the system. The design is based on heat output of the engine, radiator size, type of coolant, size of water pump (coolant pump), type of fan, thermostat, and system pressure. The cooling system must allow the engine to warm up to the required operating temperature as rapidly as possible and then maintain that temperature.

Peak combustion temperatures in the engine run from 4,000°F to 6,000°F (2,200°C to 3,300°C). The combustion temperatures will average between 1,200°F and 1,700°F (650°C and 925°C). Continued temperatures as high as this would weaken engine parts, so heat must be removed from the engine. The cooling system keeps the head and cylinder walls at a temperature that is within the range for maximum efficiency. The cooling system removes about one-third of the heat created in the engine. Another third escapes to the exhaust system.

Typical Combustion and Exhaust Temperatures inside an engine

Low Temperature Engine Problems

Engine operating temperatures must be above a minimum temperature for proper engine operation. If the coolant temperature does not reach the specified temperature as determined by the thermostat, then the following engine-related faults can occur.

• A P0128 diagnostic trouble code (DTC) can be set. This code indicates “coolant temperature below thermostat regulating temperature,” which is usually caused by a defective thermostat staying open or partially open.
• Moisture created during the combustion process can condense and flow into the oil. For each gallon of fuel used, moisture equal to a gallon of water is produced. The condensed moisture combines with unburned hydrocarbons and additives to form carbonic acid, sulfuric acid, nitric acid, hydrobromic acid, and hydrochloric acid.

To reduce cold engine problems and to help start engines in cold climates, most manufacturers offer block heaters as an option. These block heaters are plugged into household current (110 volts AC) and the heating element warms the coolant.

High Temperature Engine Problems

Maximum temperature limits are required to protect the engine. Higher than normal temperatures can cause the following engine-related issues.

• High temperatures will oxidize the engine oil producing hard carbon and varnish. The varnish will cause the hydraulic valve lifter plungers to stick. Higher than normal temperatures will also cause the oil to become thinner (lower viscosity than normal). Thinned oil will also get into the combustion chamber by going past the piston rings and through valve guides to cause excessive oil consumption.
• The combustion process is very sensitive to temperature. High coolant temperatures raise the combustion temperatures to a point that may cause detonation (also called spark knock or ping) to occur.

Cooling System Operation

Purpose and Function

Coolant flows through the engine, where it picks up heat. It then flows to the radiator, where the heat is given up to the outside air. The coolant continually recirculates through the cooling system, as illustrated in

Cooling System Operation

The temperature of the coolant rises as much as 15°F (8°C) as it goes through the engine and cools as it goes through the radiator. The coolant flow rate may be as high as 1 gallon (4 liters) per minute for each horsepower the engine produces.

Coolant circulates through the water jackets in the engine block and cylinder head

Hot coolant comes out of the thermostat housing on the top of the engine on most engines. The engine coolant outlet is connected to the radiator by the upper radiator hose and clamps. The coolant in the radiator is cooled by air flowing through the radiator. As the coolant moves through the radiator, it cools. The cooler coolant leaves the radiator through an outlet and the lower radiator hose, and then flows to the inlet side of the water pump, where it is recirculated through the engine.

• NOTE: Some newer engine designs such as Chrysler’s 4.7 liter V-8 and General Motor’s 4.8, 5.3, 5.7, and 6.0 liter V-8s place the thermostat on the inlet side of the water pump. As the cooled coolant hits the thermostat, the thermostat closes until the coolant temperature again causes it to open. Placing the thermostat in the inlet side of the water pump therefore reduces the rapid temperature changes that could cause stress in the engine, especially if aluminum heads are used with a cast iron block.

Radiators are designed for the maximum rate of heat transfer using minimum space. Cooling airflow through the radiator is aided by a belt- or electric motor–driven cooling fan.

Next Steps towards ASE Certification

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Diesel engines can be diagnosed using a scan tool in most cases, because most of the pressure sensors values can be displayed. Common faults include:

• Hard starting
• No start
• Extended cranking before starting

Compression Testing

Compression Gauge that is designed for the higher compression rate of a diesel engine

A compression test is fundamental for determining the mechanical condition of a diesel engine. Worn piston rings can cause low power and excessive exhaust smoke. To test the compression on a diesel engine, the following will have to be done.

1. Remove the glow plug (if equipped) or the injector.
2. Use a diesel compression gauge, as the compression is too high to use a gasoline engine compression gauge.

A diesel engine should produce at least 300 PSI (2,068 kPa) of compression pressure and all cylinders should be within 50 PSI (345 kPa) of each other.

Glow Plug Resistance Balance Test

Glow plugs increase in resistance as their temperature increases. All glow plugs should have about the same resistance when checked with an ohmmeter. A similar test of the resistance of the glow plugs can be used to detect a weak cylinder. This test is particularly helpful on a diesel engine that is not computer controlled. To test for even cylinder balance using glow plug resistance, perform the following on a warm engine.

1. Unplug, measure, and record the resistance of all glow plugs.
2. With the wires still removed from the glow plugs, start the engine.
3. Allow the engine to run for several minutes to allow the combustion inside the cylinder to warm the glow plugs.
4. Measure the plugs and record the resistance of all glow plugs.
5. The resistance of all glow plugs should be higher than at the beginning of the test. A glow plug that is in a cylinder that is not firing correctly will not increase in resistance as much as the others.
6. Another test is to measure exhaust manifold temperature at each exhaust port using an infrared thermometer or a pyrometer. Misfiring cylinders will run cold.

Injector Pop Testing

Typical Pop Tester Used to Check the Spray Pattern of a Diesel Injector

A pop tester is a device used for checking a diesel injector nozzle for proper spray pattern. The handle is depressed and pop-off pressure is displayed on the gauge.

The spray pattern should be a hollow cone, but will vary depending on design. The nozzle should also be tested for leakage (dripping of the nozzle) while under pressure. If the spray pattern is not correct, then cleaning, repairing, or replacing the injector nozzle may be necessary.

Next Steps towards ASE Certification

Now that you’re familiar with Compression Testing, Glow Plug Resistance Balance, and Injector Pop Testing, try out our free Automotive Service Excellence Tests to see how much you know!

Purpose and Function

There is a normal operating temperature range between low-temperature and high-temperature extremes. The thermostat controls the minimum normal temperature. The thermostat is a temperature-controlled valve placed at the engine coolant outlet on most engines.

Thermostat Operation

An encapsulated wax-based plastic pellet heat sensor is located on the engine side of the thermostatic valve. As the engine warms, heat swells the heat sensor.

A cross section of a typical wax-actuated thermostat showing the position of the wax pellet and spring

A mechanical link, connected to the heat sensor, opens the thermostat valve. As the thermostat begins to open, it allows some coolant to flow to the radiator, where it is cooled. The remaining part of the coolant continues to flow through the bypass, thereby bypassing the thermostat and flowing back through the engine.

(a) When the engine is cold, the coolant flows through the bypass. (b) When the thermostat opens, the coolant can flow to the radiator

The rated temperature of the thermostat indicates the temperature at which the thermostat starts to open. The thermostat is fully open at about 20°F higher than its opening temperature.
If the radiator, water pump, and coolant passages are functioning correctly, the engine should always be operating within the opening and fully open temperature range of the thermostat.

Thermostat Testing

Thermostat Testing

There are three basic methods used to check the operation of the thermostat.

1.  Hot water method. If the thermostat is removed from the vehicle and is closed, insert a 0.015 in. (0.4 mm) feeler gauge in the opening so that the thermostat will hang on the feeler gauge. The thermostat should then be suspended by the feeler gauge in a container of water or coolant along with a thermometer. The container should be heated until the thermostat opens enough to release and fall from the feeler gauge. The temperature at which the thermostat falls is the opening temperature of the thermostat. If it is within 5°F (4°C) of the temperature stamped on the thermostat, the thermostat is satisfactory for use. If the temperature difference is greater, the thermostat should be replaced.

Checking the opening temperature of a thermostat

2. Infrared thermometer method. An infrared thermometer (also called a pyrometer) can be used to measure the temperature of the coolant near the thermostat. The area on the engine side of the thermostat should be at the highest temperature that exists in the engine. A properly operating cooling system should cause the pyrometer to read as follows:

• As the engine warms, the temperature reaches near thermostat opening temperature.
• As the thermostat opens, the temperature drops just as the thermostat opens, sending coolant to the radiator.
• As the thermostat cycles, the temperature should range between the opening temperature of the thermostat and 20°F (11°C) above the opening temperature.

NOTE: If the temperature rises higher than 20°F (11°C) above the opening temperature of the thermostat, inspect the cooling system for a restriction or low coolant flow. A clogged radiator could also cause the excessive temperature rise.

3. Scan tool method. A scan tool can be used on many vehicles to read the actual temperature of the coolant as detected by the engine coolant temperature (ECT) sensor. Although the sensor or the wiring to and from the sensor may be defective, at least the scan tool can indicate what the computer “thinks” is the engine coolant temperature.

Next Steps towards ASE Certification

Now that you’re familiar with Diesel Engine Thermostats, try out our free Automotive Service Excellence Tests to see how much you know!