Thermostat Test

The thermostat should be replaced only after the following tests have been performed:
1. Heat Test
89° C (192° F) Thermostat
Immerse the removed thermostat in a 89°C (192°F) solution of antifreeze and water mixture. An 89°C (192°F) thermostat should open to 0.08 mm (0.0003 inch). When immersed in a 100° C (212° F) solution, the thermostat should open to 3.2 mm (1/8 inch).
92° C (197° F) Thermostat
A 92°C (197°F) thermostat immersed in a 92°C (197°F) solution of antifreeze and water should open to O.O8 mm (0.0003 inch), when immersed in the 100° C (212° F) solution, the thermostat should open 3.2 mm (1/8 inch).
2. Visual Test
a. If heat is not available, the thermostat should be checked for leakage. This is done by holding the thermostat up to a lighted background. Leakage of light around the thermostat valve (thermostat at room temperature) indicates that the thermostat should be replaced with an original equipment, approved thermostat. Some thermostats have a small leakage notch at one location on the perimeter of the thermostat valve which is considered normal.