The temperature stick is a pencil-like device that has a wax material containing chemicals which melt at a given temperature. Use the temperature sticks in order to determine a thermostat's operating temperature. Rub the following sticks on the thermostat housing:

The marks made by the sticks should melt when coolant temperatures reach the corresponding temperatures. These temperatures are the normal operating range of the thermostat.

1. Relieve the pressure and remove the radiator cap. Refer to Cooling System Draining and Filling .
2. Rub a 97°C (206°F) J 24731 .
3. Warm up the engine at fast idle.
4. Check for coolant flow before the mark begins to melt.

Is there coolant flow before the mark melts?

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Go to Step 2

Go to Step 3

The problem is caused from something other than the thermostat. Refer to Engine Fails To Reach Normal Operating Temperature .

Does the engine still overheat?

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System OK

1. Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .
2. Check the system.

Is the engine still overheating?

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System OK

The temperature stick is a pencil-like device that has a wax material containing chemicals which melt at a given temperature. Use the temperature sticks in order to determine a thermostat's operating temperature. Rub the following sticks on the thermostat housing:

1. Relieve the pressure and remove the radiator cap. Refer to Cooling System Draining and Filling .
2. Rub a 87°C (188°F) J 24731 .
3. Warm up the engine at fast idle.
4. Check for coolant flow before the mark begins to melt.

Is there coolant flow before the mark melts?

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Go to Step 3

Go to Step 2

The problem is caused from something other than the thermostat. Refer to Engine Fails To Reach Normal Operating Temperature .

Does the engine warm up properly?

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System OK

1. Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .
2. Check the system.

Is the engine still overheating?

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System OK