Thermostat: Testing and Inspection

Overheating, or failure to reach normal operating temperature, can indicate improper water thermostat operation. The water thermostat must be removed from the vehicle and temperature tested.





1. Suspend the water thermostat and an accurate thermometer in a suitable container. Do not allow the test pieces to touch the bottom.
2. Fill the container with water to completely cover the water thermostat.
3. Heat the water until boiling, and observe the thermometer temperature.





4. The water thermostat should initially open at 80-84° C (176-183° F), and be fully open at 95° C (203° F).

NOTE: Fully open means the water thermostat lifts a distance of 8.5 mm (0.33 inch) or more.

5. Start to cool the water thermostat.
6. The water thermostat should be closed at 79° C (174° F).
7. If the water thermostat does not operate as indicated, replace the water thermostat. Otherwise, return to the Pinpoint Tests. Pinpoint Tests

To check for low temperature leakage, cool the water thermostat to room temperature and hold it up against a lighted background. Check for light visible between the valve and the valve seat. If light is visible, replace the water thermostat.