Use one of the following procedures in testing for a malfunctioning thermostat:

The coolant thermostat can be tested using a temperature, or tempil, stick. The tempil stick is a pencil-like device. The tempil stick has a wax material containing certain chemicals which melt at a given temperature. Temperature sticks can be used to determine a thermostat's operating range, by rubbing 87°C (188°F) and 97°C (206°F) sticks on the thermostat housing.

1. Use a J 24731 Tempil Stick in order to find the opening and the closing temperatures of the coolant thermostat.

•	J 24731-188 tempil stick melts at 87°C (188°F). The thermostat should begin to open.

•	J 24731-206 tempil stick melts at 97°C (206°F). The thermostat should be fully open.

2. Replace the coolant thermostat if the thermostat does not operate properly between this temperature range.

Inspect the operation of the thermostat by hanging the thermostat on a hook in a 33 percent glycol solution.

In order to inspect if the thermostat valve is opening properly, perform the following test:

1. Completely submerge the thermostat in a glycol solution. The solution should be 11°C (22°F) above the temperature indicated on the thermostat valve.
2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should open.

In order to inspect if the thermostat valve is closing properly, perform the following test:

1. Completely submerge the thermostat in a glycol solution. The solution should be 6°C (10°F) below the temperature indicated on the thermostat valve.
2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should close completely.