GM Service Manual Online
For 1990-2009 cars only

For detailed thermostat diagnostic procedures. Refer to Diagnostic System Check .

Thermostat Test

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.

Tools Required

    • J 24731 -188 188°F Tempilstick
    • J 24731 -206 206°F Tempilstick
  1. Use a tempilstick in order to find the opening and the closing temperatures of the coolant thermostat.
  2. • 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.
  3. Replace the coolant thermostat if it does not operate properly between this temperature range.