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Testing Thermostat

Test the thermostat when it is removed from the engine. It is also wise to perform this simple test to a new thermostat before installation.

Measure the thermostat to determine the change in length between cold and hot conditions, as shown in Fig. 4-6. Heat the thermostat in a pan of water as shown in Fig. 4-7 while monitoring temperature with a thermometer.

Fig. 4-6. Thermostat length. Dimension a is closed (cold) length; dimension b is open (hot) length.

Fig. 4-7. Testing thermostat in hot water.

The thermostat should begin to open at approximately 185°F (85°C). At boiling temperature, approximately 212°F (100°C), the length as shown in Fig. 4-6 should be at least 7 mm (9/32 in.) greater than the cold length measured earlier. A thermostat which does not open the full amount should not be installed.

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