The coolant thermostat can be tested using a temperature (tempil) stick. The temperature stick is a pencil like device. It 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 tempilstick in order to find the opening and the closing temperatures of the coolant thermostat.

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

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

2. Replace the coolant thermostat if it does not operate properly between this temperature range. Refer to Engine Coolant Thermostat Replacement .