Make sure the valve spring is tight when the thermostat is fully closed. If the spring is not tight, replace the thermostat.
Suspend the thermostat and a thermometer in a pan of 50/50 mixture of ethylene glycol and water. Do not let the thermostat or the thermometer rest on the bottom of the pan because the uneven concentration of heat on the bottom could result in inaccurate temperature measurements.
Heat the pan on a burner.
Use the thermometer to measure the temperature of the heated solution.
The thermostat should begin to open at 82° C (180° F) and it should be fully open at 95° C (203.4° F) and it should be fully close at 80° C (176.4° F). If it does not open or close at these temperature, replace the thermostat. Also, the thermostat rod's stroke from the initially open to the fully open should be 8 mm (0.32 in).
