Cooling System Diagnosis – Overheating
1. Check the coolant level in the following steps:
A. Observe the level in the coolant reservoir:
• If the level is low, go to step B.
• If the level is correct, check the drive belt.
B. Remove the radiator cap (engine cool) and observe the coolant level:
• If the level is low, go to step C.
• If the level is correct, check the drive belt.
C. Check for external leakage:
• If no leakage is visible, go to step D.
• If leakage is visible, make repairs and re-check the cooling system operation.
D. Check cooling system pressure
• If the system maintains pressure, go to step E.
• If the system loses pressure, locate the source of the leakage, make repairs and check the cooling
system operation.
E. Check the coolant mixture concentration:
• If the coolant mixture is correct, check the drive belt.
• If the mixture concentration is incorrect, change it and check the cooling system operation.
2. Check the drive belt in the following steps:
A. Check drive belt tension and condition (see Figure 4-16):
• If the tension and condition are good, check the condition of the hoses.
• If the tension is low, go to step B.
• If the condition is poor, replace the drive belt and check the cooling system operation.
B. Check the drive belt tensioner operation:
• If the tensioner checks good, replace the drive belt and check the cooling system operation.
• If the tensioner checks bad, replace it and check the cooling system operation.
3. Check the condition of the hoses:
• If all hoses check good, check the thermostat operation.
• If any hose is collapsed, replace it and check the cooling system operation.
4. Check the thermostat opening temperature (refer to page 4-18):
• If the opening temperature is correct, check the radiator.
• If the opening temperature is high, replace the thermostat and check the cooling system operation.
5. Check the radiator in the following steps:
A. Check the airflow through the radiator:
• If the airflow is unrestricted, check the coolant flow.
• If the airflow is restricted, repair and check the cooling system operation.
B. Check the coolant flow through the radiator:
• If the coolant flow is unrestricted, check the cylinder case and head passages for restrictions.
• If the coolant flow is restricted, repair the radiator and check the cooling system operation.
6. Check the cylinder case and head passages in the following steps (see Figure 4-15):
A. Check the coolant flow:
• If the coolant flow is unrestricted, check for combustion gas flow into the cooling system.
• If the coolant flow is restricted, replace the faulty component and check the cooling system operation.
B. Check combustion gas flow:
• If no combustion gas flow into the cooling system exists, check the water pump.
• If combustion gas flow into the cooling system is evident, replace the faulty component and check the cooling system operation.
7. Remove and check the water pump operation (see Figure 4-16):
• If the condition of the impeller and passages is good, check other factors.
8. Check the fan clutch operation (refer to the diagnostic hints on page 4-15):
• If the fan clutch applies, refer to other factors.
• If the fan clutch does not apply, replace it and check the cooling system operation.
9. Check other factors for overheating:
• Operation of the vehicle under heavy loads
• Air conditioning system operation
• High oil level
• Restriction in airflow to the radiator
• Extremely high ambient temperature
Cooling System Thermostat Diagnosis
1. Check for low opening temperature in the following steps:
A. Remove the radiator cap (cool engine).
B. Rub a 188° F (86.6° C) temperature crayon on the thermostat housing (see Figure 4-17).
C. Start and run the engine at a fast idle speed.
D. Watch for coolant flow in the radiator before the temperature crayon begins to melt:
• If coolant does not flow before the temperature crayon mark melts, check for other causes.
• If coolant flows before the temperature crayon mark melts, replace the thermostat and check the cooling system operation.
2. Check for high opening temperature in the following steps:
A. Remove the radiator cap (cool engine).
B. Rub a 206° F (96.6° C) temperature crayon on the thermostat housing.
C. Start and run the engine at a fast idle speed.
D. Watch for coolant flow in the radiator before the temperature crayon begins to melt:
• If coolant flows before the temperature crayon mark melts, check for other causes.
• If coolant does not flow before the temperature crayon mark melts, replace the thermostat and check the cooling system operation.
