The thermostat test requires that the thermostat be removed from the vehicle. Refer to Engine Coolant Thermostat Replacement in Engine Cooling.

1. Suspend the thermostat (1) and a thermometer (3) in a pan in a 50/50 mixture of ethylene glycol and water. Do not let the thermostat (or thermometer) rest on the bottom of the pan because of the uneven concentration of heat. This could result in inaccurate temperature measurements.
2. Place the pan on a burner (2).
3. Heat the solution.
4. Measure the temperature of the solution by using a thermometer (3).
5. The thermostat valve opening temperature should be 80° to 84°C (176° to 183° F). The valve lift should be 8 mm (0.31 in) or more at 95°C (203°F).
6. Replace the thermostat (1) If either of the preceding specifications are not met.
7. Ensure that the valve spring is tight when the thermostat is fully closed.
8. Replace the thermostat If the spring is not tight.