A thermostat that stays closed or only partly open restricts the flow of coolant in the system. This condition causes the engine to overheat. A thermostat that is stuck in the full open position does not allow the engine to reach the normal operating temperature. Cold engine operation causes a buildup of excess carbon deposits on the following components:

Use the following procedure to verify correct thermostat operation:

1. Remove the thermostat. Refer to Engine Coolant Thermostat Replacement .



2. Suspend the thermostat and a thermometer in water. Place the thermometer close to the thermostat.
3. Heat the water.
4. Record the temperature when the thermostat begins to open.
5. Record the temperature when the thermostat is open.
6. Compare the temperature reading with Specifications in this section. Refer to Engine Cooling System Specifications .
7. Replace the thermostat and the gasket as needed. Refer to Engine Coolant Thermostat Replacement .
8. Fill the cooling system. Refer to Cooling System Draining and Filling .
9. Run the engine until the engine reaches normal operating temperature.
10. Check for coolant leaks around the coolant outlet and the gasket.
11. Check the coolant level. Add coolant as needed.
12. Install the radiator cap.