LO 11-8 Outline maintenance procedures and identify tools and methods used to perform maintenance on a diesel engine cooling system

1. Maintenance of Cooling Systems

Maintenance of Cooling Systems

This chapter on cooling systems is lengthy not only because of the wide range of technology used in cooling systems but also because of the disproportionate influence the cooling system has on potential engine failures and maintenance. Approximately 40% of all engine maintenance or breakdown is related directly or indirectly to cooling system maintenance, so technicians need to be familiar with common service practices and diagnostic procedures.

Service Tools

A properly trained and experienced technician will use special tools for diagnosing and servicing the engine cooling system. These tools include Figure 70:

A	B		FIGURE 11-71: A coolant refill tool draws a vacuum into the cooling system and uses the negative pressure to refill the cooling system without forming any air pockets.
FIGURE 11-70: Common tools needed to service cooling systems: A. Pressure tester. B. Refractometer.

• Coolant system pressure tester: A pressure tester is used to apply pressure to the cooling system in order to identify the source of external coolant leaks. Under pressure, coolant may also leak internally to the combustion chamber, intake or exhaust system, air compressors, and EGR coolers and also into liquid air charge coolers or lubricating oil.
• Hydrometer: A hydrometer is used to measure coolant density in order to determine its freeze protection. When measuring the specific gravity of the coolant, use a purpose-made hydrometer designed specifically for the type of antifreeze base.
• Refractometer: A refractometer is used to measure coolant concentration and freeze protection by evaluating the fluid’s refractive index (ability to bend light). This refractometer can be used with ethylene glycol– and propylene glycol–types of coolant.
• Coolant test strips: These strips are used to quickly evaluate a number of variables, such as the coolant pH, percentage of nitrite or nitrate, presence of corrosion inhibitors, and even freeze protection. The capabilities of the strips are price sensitive, with more features making the tests proportionately more expensive.
• Coolant tracing dye: To identify coolant leaks, tracing dye is sometimes added to the coolant. Using an ultraviolet (UV) light source (black light), the location of a leak is easily identified because the dye becomes fluorescent under the black light.
• Infrared thermometer: This is a noncontact thermometer used to measure the actual surface temperatures of various components throughout the cooling system. It is helpful to quickly identify under- or overcooled components in order to pinpoint the location of system flow restrictions.
• Thermometer: A thermometer is used to measure the temperature of air exiting the heating ducts.
• Voltmeter: A voltmeter is used to identify electrical problems in various areas, such as cooling system sensors and fan control circuits.
• Belt-tension gauge: This gauge is used to check belt tension in older V-belt drive systems. Loose belts slip and prevent proper circulation of coolant.
• Serpentine belt-wear gauge: These gauges are used to check whether the serpentine belt grooves are excessively worn, which allows the belts driving the water pump or fan to slip.
• Alkaline cleaning agents: These agents are used to clean cooling systems of oil and fuel contamination. They are generally more effective than powdered nonfoaming detergents. Use of any particular cooling system cleaners must be checked to verify that they are safe for aluminum radiator and heater cores. These types of cleaners are also capable of removing silicate deposits.
• Mild, acid-based cleaning agents: These agents are used to safely remove rust, corrosion, scale, and solder particles without disassembling the cooling system.
• Electronic service tools (ESTs) : Commonly called a scan tool or used with a laptop running OEM or other software, these tools activate the cooling fan through bidirectional communication. Fan timers are used to control minimum fan run-time speeds to reduce on/off fan clutch wear and are adjusted using OEM software. Diagnostic trouble codes (DTCs) related to the cooling system are read and cleared using OEM software
• Coolant refill/air purge tool: This tool is used to refill a cooling system after it has been drained. Many of these tools are universal, using a venturi and compressed air to pull a vacuum into the entire cooling system. When evacuated, the negative cooling system pressure draws in coolant from a container and does not permit air to enter the system. This method ensures that no air pockets are left in the cooling system as a result of refilling. Use of these tools is mandated by some OEMs in order to prevent coolant voids in places like the EGR or oil cooler and potential for the absence of coolant to create hot spots that burn and damage those components after start-up Figure 71.

1.1. Visual Inspection

Visual Inspection

A visual inspection of the cooling system is performed first to identify obvious system defects.

1. Verify that the belts, hoses, hose clamps, radiator caps, surge tanks, fan clutch, fan, fan shroud, and other system components are all present and functioning.

• Inspect the radiator for damage, the cooling fins for obstructions, and the core for translucence. If the radiator core is not too thick, a light shined through the radiator should be easily seen on the opposite side.
• Squeeze hoses to verify that they are not hardened or cracking. Electrolytic action can cause hoses to deteriorate from the inside out. Unusually soft hoses indicate internal deterioration.
• Inspect the accessory drive pulley and belt tensioners for correct operation and alignment.
• Inspect the operation of the heater to verify that warm air blows from the ventilation ducts when placed in heater mode.
• Check for the smell of coolant when the heater is blowing.
• Inspect the heating, ventilation, and air-conditioning (HVAC) module drain tube for leaking coolant.
• Retrieve fault codes.

2. Inspect the level and quality of the coolant in the surge tank and radiator.

• Observe and record the color and condition of the coolant while inspecting the level and quality in order to determine whether the correct type of coolant is in use and whether it is contaminated with oil, fuel, or silicate.
• Measure the freeze protection of the coolant with an appropriate refractometer or hydrometer to match the coolant-type base (ethylene glycol, propylene glycol, or glycerin).
• Using a test strip, measure the additive levels in the cooling system. In anything but NOAT coolant, nitrite/nitrate should be present.
• Verify that the correct level of coolant additives are present. Note that the test strips may be temperature sensitive. Do not use test strips in hot coolant. Allow the coolant to cool in a container for several minutes before testing.

3. Examine the engine for external coolant leaks.

• Inspect the engine oil level and the color of the engine oil to verify that there is no coolant contamination. Sample engine oil and have an oil analysis performed if no identifiable external leaks are detected to account for coolant loss.
• Drain the air tank reservoirs to inspect for coolant leakage into the air compressor.
• Inspect the water pump weep hole for a leakage or dried coolant track.
• Reinspect hoses and clamps for any collapsed hoses, deterioration, leaks, or chaff.
• After pressure testing the engine, pressure test the radiator cap. It should release pressure at no more than plus or minus 2 psi.
• Pressure test the vacuum valve and inspect both the cap’s pressure and the vacuum seals to verify that they are in good condition. Any damage to the seals requires cap replacement.

4. Operate the engine and observe the exhaust smoke color.

• Verify that the coolant reaches operating temperature within an acceptable amount of time.
• White exhaust smoke may indicate coolant leaks into the combustion chamber through a defective head gasket, cracked cylinder head, or leaking EGR cooler.
• With the radiator cap removed or with it on, if possible, inspect the coolant vent lines entering the surge tank to determine whether gas bubbles of excessive size or number are entering the surge tank. Some vaporized steam bubbles should be present from the vent lines connecting the tank to the engine, but excessive bubbling may indicate a cavitated liner or block or a cracked cylinder head.
• Air-operated switches and valves connected to the cooling system, such as water control valves for the cab and bunk heaters, may give a false positive for an internal engine leak. A cracked air compressor casting may give the same indication. Open the air reservoir drain valves while running the engine to eliminate the likelihood of a defective air compressor pressurizing the cooling system. The gaskets and seals on the radiator cap should be inspected for any cracks or damage.

1.2. Pressure Testing the Cooling System and Checking for Leaks

Pressure Testing the Cooling System and Checking for Leaks Pressure test the cooling system, particularly if there is a complaint about the loss of coolant. Pressure testing the cooling system is an effective way to locate external and internal coolant leaks. High cooling system pressure causes coolant to leak out much more quickly from a crack, hole, leaking gasket, or seal, which makes leaks easier to locate. Adding dye to the engine coolant allows coolant leaking into heat exchangers to be more easily identified with a UV light. The dye must be added to and circulated in a warm engine before inspecting for leaks. Loose hose clamps often cause cold leaks and can be detected more easily when the engine is off. Other leaks, such as head gasket leaks and those resulting from cracked or porous castings, may only be detected after the engine is operated under load at operating temperature. The cooling system pressure cap should also be tested because a defective or leaking cap will fail to pressurize the cooling system, resulting in coolant loss Figure 72. To pressure test the cooling system and check for leaks, follow the steps in Skill Drill 11-1.     Technicians Tip     If you need to replace a pressure cap, use only a cap with the recommended pressure, not a cap with higher pressure. Diesel engines often use caps with lower pressure in order to protect the engine oil from overheating in the oil cooler. Caps with lower pressure will allow coolant to boil at a lower temperature, enabling the escaping steam to carry away excess heat.

FIGURE 11-72: Pressure testing a radiator cap.

1.3. Video: Pressure Testing Cooling System

1.4. SKILL DRILL 11-1  Pressure Testing the Cooling System and Checking for Leaks

STEP 1 With the engine off, top off the engine coolant level with premixed coolant. STEP 2 With the engine off, connect the radiator pressure tester in place of the pressure cap. Larger caps, which are found on HD cooling systems, or unique OEM pressure cap designs may not fit with a standard pressure cap tester. An adapter may be required to seal the tool to the neck of the surge tank or radiator. STEP 3 Pressurize the system to 15–17 psi (103–117 kPa). STEP 4 Observe the pressure readings for 30 minutes. During this time, visually inspect the cooling system hoses, all the connections, auxiliary coolant heaters, bunk and cab heaters, EGR coolers, EGR valves, turbocharger coolant lines, the water pump weep hole, all gasket sealing surfaces, and any other components that have coolant flow. STEP 5 Check the engine oil level and verify that the oil has a normal color. Oil that looks milky likely has coolant leaking into it. Verify that coolant is not leaking into the oil by sampling and performing an oil analysis. STEP 6 Inspect the seals on the pressure cap and pressure test the cap. The seals should be intact and in good condition without any cracks. The same pressure tester used to test the engine is also used to test the cap. Place an adapter between the cap and the test tool and pump the tester once again. The cap’s release pressure should be indicated on the cap, and it should hold pressure until the tester applies the amount of pressure specified on the cap. STEP 7 Refer to the OEM service information to check whether the pressure cap is correctly rated for the vehicle. If the cap will not hold or cannot reach specified pressure, or if it does not vent at the specified pressure, then replace it with a new cap with the correct pressure rating. STEP 8 Record and report your results. STEP 9 If there is a significant drop in pressure and the complaint is related to coolant loss, the engine may have an internal coolant leak. Using a separate procedure, the engine should be checked first to determine whether the cooling system is excessively pressurized when operating. The EGR cooler should be inspected as well using a separate procedure. STEP 10 To check for internal leaks, drain the engine oil and remove the oil pan. STEP 11 With the cooling system still pressurized, observe whether the liner O-rings are leaking or whether coolant is emerging from a head gasket leak. In pushrod engines, head gasket leaks drip coolant from the cam side of the engine. STEP 12 Remove the EGR outlet hose or tube and inspect for the presence of coolant.

1.5. Verifying the Engine Operating Temperature

Verifying the Engine Operating Temperature
Technicians need to verify whether an engine is reaching operating temperature whenever there is a complaint about an engine overheating or overcooling. Overcooling takes place when the engine does not reach operating temperature. Observations about how long the engine takes to reach operating temperature and the maximum coolant temperature are recorded in these instances. Also inspected for excessive operating temperature are the fault codes associated with the OBD system or the engine protection system logs. The heavy-duty on-board diagnostics (HD-OBD) cooling system monitor also logs codes if the engine does not warm to operating temperature quickly enough to enable other monitors to run. Validate the operating temperature reported by the coolant temperature gauge using an infrared thermometer while investigating excessive operating temperature fault codes. To verify the engine operating temperature, follow the steps in Skill Drill 11-2.

1.6. Video: Temperature Indicators

1.7. Anim: Gauges Instruments & Warning Systems

1.8. Anim: Engine Temperature Testing

1.9. SKILL DRILL 11-2  Verifying Engine Operating Temperature

1.10. Inspecting for a Leaking Exhaust Gas Recirculation Cooler

Inspecting for a Leaking Exhaust Gas Recirculation Cooler
Loss of engine coolant without any visible external leaks may be caused by a variety of internal leaks. Additionally, over-pressurizing the cooling system can force coolant out of the overflow tank while leaking head gaskets and air compressors can consume coolant. A more common problem is a cracked EGR cooler, which can either over-pressurize the cooling system or allow engine coolant to leak into the cooler where it is mixed with exhaust gas and delivered to the engine intake. White exhaust smoke that smells sweet is an indication of an EGR cooler leak. The problem can worsen under hard acceleration. To inspect for a leaking EGR cooler, follow the steps in Skill Drill 11-3.

1.11. SKILL DRILL 11-3  Inspecting for a Leaking Exhaust Gas Recirculation Cooler

STEP 1 Pressurize the cooling system and inspect for obvious external leaks. STEP 2 Remove the EGR valve and inspect it to see if it looks wet and shiny. If the EGR valve is located after the EGR cooler, coolant leaks will wet the valve. EGR valves on the hot side of the EGR system will not become wetted with coolant. STEP 3 With the cooling system pressurized, disconnect the outlet pipe of the cooler and check for visible leaks. STEP 4 Disconnect the EGR cooler inlet and outlet exhaust pipe. Using a block-off kit with a pressure adapter, plug the exhaust inlet and outlets and tighten the block-off plate adapters using the EGR clamps. STEP 5 Pressurize the exhaust side of the EGR cooler using the block-off kit with shop air supplied at 30 psi (207 kPa). STEP 6 Shut off the compressed air to the cooler while it is pressurized and wait 30 minutes. There should be no pressure drop in 30 minutes. Any drop indicates that the cooler is defective. STEP 7 Check for air bubbles in the surge tank and from the vent lines. If air bubbles are present, replace the EGR cooler.

1.12. Testing Coolant Nitrite or Diesel Coolant Additive/Supplemental Coolant Additive Levels

Testing Coolant Nitrite or Diesel Coolant Additive/Supplemental Coolant Additive Levels
Nitrite is the most important additive used in diesel coolant because it prevents cavitation damage in the cooling system. Nitrite is one of the ingredients present in DCA and SCA coolant conditioner packages. Coolant filters also have a specific level of nitrite that requires matching a coolant filter with the cooling system maintenance requirements. In engines that use conventional type I antifreeze, nitrite levels should be checked at every oil change. For engines using ELC, nitrite levels should be checked once or twice a year. Different nitrite levels are required depending on the antifreeze formulation used. Type I requires 3–5% nitrite levels, but long-life formulations require substantially less. A coolant test strip that contains at least three kinds of chemically treated testing pads should be used: one for antifreeze concentration, another for nitrite levels, and another for pH. Additional pads can be found on test strips for testing other corrosion inhibitors. To test coolant nitrite or DCA/SCA levels, follow the steps in Skill Drill 11-4.

1.13. SKILL DRILL 11-4  Testing Coolant Nitrite or Diesel Coolant Additive/Supplemental Coolant Additive Levels

STEP 1 Identify the type of coolant formulation based on coolant color. The decal next to the surge tank may not be correct if the coolant has been changed or contaminated with other coolant formulations. STEP 2 Using an OEM or aftermarket test strip, dip the strip into the coolant and shake any excess coolant off the strip. STEP 3 Using the chart on the test strip bottle, compare the color of the nitrite pad on the test strip against the chart scales. STEP 4 Determine the level of nitrite in the cooling system in parts per million or as a percentage. STEP 5 Using the service manual or test strip manufacturer’s recommendations, determine the amount of nitrite that may be needed based on the coolant formulation. The level may be acceptable, too high, or too low. STEP 6 Drain the coolant to correct excessive nitrite levels, which can lead to deterioration of cooling system components, particularly hoses. Add the correct amount of extender, DCA, or SCA based on the cooling system capacity and coolant formulation.

1.14. Maintenance Tips

Maintenance Tips

The unique requirements of diesel engine cooling systems make it important to keep in mind a number of points when servicing diesel engine cooling systems. These include:

• The cooling system must be maintained on a regular basis to prevent overheating, cavitation, corrosion, scale, and gelation due to silicate dropout.
• Cracked cylinder heads and leaking head gaskets can cause coolant to leak into the engine, leading to catastrophic engine failure.
• Overconcentration of DCA or overconcentrated antifreeze can lead to silicate dropout.
• Conventionally formulated coolant should be changed and the cooling system flushed every 2 years.
• Corrosion-inhibitor packages contained in engine coolant can be damaged through overheating and should be discarded and not reused.
• It is recommended to pressure test cooling systems at 15–18 psi (103–124 kPa) to check for leaks. The pressure should hold for several minutes without significantly dropping. The engine should be inspected for external leaks after pressure testing. The adapter circled in Figure 3 is used with the pressure tester to check the radiator cap. The radiator cap should only release pressure at the rating on the cap.
• The concentration of antifreeze should be checked not only to ensure freeze protection but also because adequate antifreeze is needed to provide enough corrosion and cavitation inhibitors to the cooling system.

1.15. Radiator Cap Inspection

Radiator Cap Inspection
The rubber gasket that seals the pressure valve at the bottom of the radiator neck should be inspected. Cracked, deteriorated, or damaged gaskets will leak, and caps with such gaskets should be discarded. When pressure testing cooling systems, the radiator cap should be simultaneously pressure checked. The cap should not leak until the pressure rating imprinted on the cap is reached.

The vacuum valve spring should also hold the vacuum valve closed when the cap is removed and no pressure is applied to the cap. A dangling vacuum valve observed when the cap is removed is evidence of a defective vacuum valve.

1.16. Evaluating Thermostatic Fan Clutches

Evaluating Thermostatic Fan Clutches
Checking by hand the amount of drag the thermostatic fan clutch has will not provide any indication of whether the clutch is operating. To evaluate these silicone fluid, thermostatic fan clutches, the amount of slippage is measured. This is best done with an optical tachometer. OEM specifications provide a specification for the percentage of the fan speed relative to engine speed when the engine is cold. This percentage increases proportionally to the temperature of the thermostatic fan clutch. Measuring both the fan speed and the engine speed with the optical tachometer will yield accurate data. Visually inspect the fan hub for any damage, looseness, fluid leaks, bearing noise, and missing or broken bolts. Any silicone fluid leakage from a hub or damaged hubs require replacement.

1.17. Hose Inspection

Hose Inspection
Air, coolant chemical attacks, and extreme temperatures all contribute to hose deterioration. As hoses age, they can become hardened and crack. Electrochemical attacks on hoses tend to affect the hoses nearest to the radiator and engine ends. Internally, hoses can soften and crack, causing lining failure and eventual hose rupture. Rubber particles loosened from the hose linings can clog radiators and thermostats. A weakened hose may collapse and restrict coolant flow. When checking the lower radiator hose, it is important to verify that the hose has not been incorrectly repaired in such a way that it would allow the hose to collapse during rapid water pump acceleration. If the radiator is restricted, a very low-pressure area is created between the pump and the radiator. Once collapsed, the hose may completely restrict coolant flow in a running engine. To prevent a hose collapse, lower radiator hoses are often made of tubular sheet metal with flexible couplers at the engine and radiator. The bottom radiator hose may also have an internal coiled spring that prevents the hose from collapsing when the engine is suddenly accelerated and the water pump draws more coolant.

The following is a recommended procedure to inspect coolant hoses for the effects of electrochemical degradation (ECD):

1. Make sure the engine is cool.
2. Use fingers and thumb to partially squeeze the hose near the clamps, or connectors, while checking for weakness. Do not use your whole hand. ECD usually occurs within 2" of the ends of the hose and not in the middle. Do not completely squeeze the hose, as too much compression can crack the inside of the hose.
3. While squeezing, feel for voids, cracks, mushiness, or weak spots near the hose ends. The heaviest damage occurs where the temperature is the hottest and air is present with the coolant. Upper radiator hoses more commonly fail first.

1.18. Preventive Maintenance for Cooling Systems

Preventive Maintenance for Cooling Systems

The following tasks help keep a diesel engine’s cooling system in good working order:

• Pressure test the radiator cap to check for the recommended system pressure level.
• Check the thermostat for proper opening and closing.
• Pressure test the system to identify any external leaks in the cooling system, including the radiator, water pump, engine cooling passages, radiator and heater hoses, cylinder head gasket, and heater core.
• Visually inspect the coolant color and condition to check for oil, transmission, and fuel leakage into the cooling system.
• Visually inspect all cooling system components, including belts, hoses, and belt tensioners.
• Test the engine fan clutch for proper operation.
• Measure the freeze protection of the coolant using a refractometer or hydrometer Figure 73.
• When conventionally formulated, type I antifreeze is used, measure nitrite/nitrate levels to indicate correct levels or DCA/SCA. This can be done using coolant test strips or other chemical tests at every oil change interval by dipping test strips into the coolant through the radiator opening. Test strips may also indicate pH level, ratio of glycol, and other levels of corrosion inhibitors. Note that test strips should not be used to check excessively hot or cold coolant. Ideally, coolant should be at room temperature for correct chemical analysis.
• Complete a lab analysis of the additive package in ELC at 300,000 miles (482,800 km). Field test kits are not currently available to evaluate levels of SCA or DCA.
• If preferred, add extender to HOAT and NOAT ELC at 300,000 miles (482,800 km).
• Flush and fill the cooling system every 200,000 miles (321,900 km) or every 2 years if conventionally formulated, type I antifreeze is used and every 600,000 miles (965,600 km) if ELC is used.

FIGURE 11-73: Verifying correct freeze protection for either propylene or ethylene glycol using a refractometer.

1.19. Preventive Maintenance Schedules

Preventive Maintenance Schedules

Preventive maintenance of the cooling system is critical for long, reliable engine life. Failure to perform required maintenance will result in cooling system failure, which can lead to breakdowns and major engine damage. OEMs publish the required maintenance for a vehicle in the owner’s manual and in the factory service information literature. The maintenance schedule lists which services are due after an accumulated distance is completed that is reported in miles (kilometres) or engine hours or date. Different types of coolant have different service intervals and can range from 24,855–93,206 miles (40,000–150,000 km) or more. Always check the OEM’s service interval schedules to ensure effective coolant operation. Belts and hoses have similar inspection and maintenance requirements. It is critical to follow these service intervals, so always check the preventive maintenance schedule for the vehicle you are working on.

1.20. Measuring Freeze Protection

Measuring Freeze Protection

The use of a hydrometer or refractometer is necessary when testing the freeze protection of the coolant in the cooling system. The customer may request this service as part of a winterization package performed by the workshop. Any time coolant is replaced in the cooling system, the freeze point should be verified after the coolant has circulated.

The hydrometer is a tool that measures the specific gravity of a liquid. When coolant is drawn into the hydrometer, a float rises to a specific level depending upon the density of the coolant. Antifreeze has a higher specific gravity than water, so the higher the float rises in the liquid, the greater the percentage of antifreeze in the mix. One drawback to hydrometers is that they are typically antifreeze specific. This means a different one may be needed to check both ethylene glycol and propylene glycol because the specific gravities of the two base liquids are different. Another drawback is that as the temperature of the coolant goes up, the specific gravity goes down. Some hydrometers have a built-in thermometer and a chart, enabling a technician to apply a correct factor for the temperature of the coolant.

A refractometer can also be used to test the proportions of antifreeze and water in the coolant mix (or the level of freeze protection) by measuring a liquid’s specific gravity. It operates by allowing light to pass through the fluid. The light bends proportionally to the particular liquid’s specific gravity. The bending of the light displays on a scale inside the tool, indicating the specific gravity of the fluid.

To use a hydrometer to test the freeze point of the coolant, follow the steps in Skill Drill 11-5. To use a refractometer to test the freeze point of the coolant, follow the steps in Skill Drill 11-6.

1.21. Video: Using Coolant Refractometer

1.22. SKILL DRILL 11-5  Using a Hydrometer to Test the Freeze Point of Coolant

STEP 1 Remove the pressure cap. Be sure the cooling system is cool before removing the cap. STEP 2 Determine the type of antifreeze and verify that the hydrometer is designed to be used with it. STEP 3 Place the hydrometer tube into the coolant and squeeze the ball on the top of the tool. STEP 4 Release the ball to draw in a sample of coolant. Make sure the level of coolant drawn in is above the minimum line. STEP 5 Read the scale on the tool to verify the freeze protection of the coolant. STEP 6 Return the coolant sample to the radiator or surge tank.

1.23. SKILL DRILL 11-6  Using a Refractometer to Test the Freeze Point of the Coolant

STEP 1 Remove the pressure cap. Be sure the cooling system is cool before removing it. STEP 2 Determine the type of antifreeze and verify that the refractometer is designed to be used with it. STEP 3 Place a few drops of coolant on the sample plate on the top of the tool. STEP 4 Hold the refractometer roughly level under a light; look through the viewfinder and read the scale to verify the freeze protection of the coolant. STEP 5 Return the coolant sample to the radiator or surge tank.

1.24. Potential Causes of Overcooling

Potential Causes of Overcooling
Overcooling is a relatively common complaint that can be caused by several different issues, including:

• A thermostat sticking open
• A blocked thermostat that is leaking
• A malfunctioning temperature gauge
• Fan drives that operate continuously

Potential Causes of Overheating
There are many potential causes of overheating as well. The following are common contributing factors:

• Low coolant
• Blocked or restricted airflow through radiator, air charge cooler, or A/C condenser
• Fan drive not working
• Missing or damaged fan shroud
• Blocked or restricted radiator
• Incorrect radiator cap
• Overconcentrated antifreeze
• Broken, slipping, or damaged water pump impeller
• Over-fueled engine
• High ambient operating temperature
• Over-pressurized cooling system from cracked cylinder head, cavitated block, defective air compressor, etc., pushing coolant out of radiator