For 1990-2009 cars

### Preliminary Diagnosis

Verify that overheating is not caused by the following conditions:

1. While pulling a trailer that is within the recommended towing weight.
2. After prolonged idle in gear, with the A/C system operating.
3. After prolonged driving in slow city traffic, traffic jams, parades, etc.

If these conditions can be eliminated as the cause of overheating, refer to the table below.

#### Engine Overheats

Possible Cause | Correction
--- | ---
Coolant fan inoperative | Refer to Cooling Fan Circuit Diagnosis
Thermostat stuck in closed position | Replace the thermostat . Refer to Engine Coolant Thermostat Replacement .
Radiator fins obstructed | Remove or relocate add-on parts that block air to the radiator. Clean away bugs, leaves, etc. In cold climates, clear away snow, etc. from the radiator core. Refer to Radiator Cleaning .
Surge tank outlet hose pinched or kinked (especially at radiator) | Relieve kinks by re-routing. Replace the hose if necessary.
Incorrect radiator | Check the radiator usage chart in a parts catalog. If needed, replace with the correct radiator.
Loss of system pressure | Pressure check system and surge tank cap Ensure the correct cap is being used.
Loose, damaged and or missing air seals or deflector | Repair or replace as required.
Cooling system passages blocked |

1. Remove the obstruction.
2. Flush the cooling system as required.
3. Refill with coolant. Refer to Cooling System Draining and Filling .

Malfunctioning coolant pump (eroded or broken impeller blades) | Replace the coolant pump. Refer to Water Pump Replacement .
Air trapped in cooling system | Refill the cooling system. Refer to Cooling System Draining and Filling .

1. Verify that the cooling system is properly filled. Refer to Cooling System Draining and Filling .
2. If the complaint is a low temperature gauge reading, check the temperature gauge for proper operation. Connect a Scan Tool to the vehicle and read the system temperature.
3. Compare this reading to the temperature gauge.
4. Replace the gauge or switch if necessary.
5. If the complaint is no heat from the HVAC system, refer to Heating Insufficient in HVAC Systems with AC - Manual.
6. Verify the proper operation of the thermostat. Refer to Thermostat Diagnosis .