Operation

OPERATION

The engine cooling thermostat is a wax pellet driven, reverse poppet choke type. The thermostat is designed to provide the fastest warm up possible by preventing leakage through it and to guarantee a minimum engine operating temperature of 88 to 93° C (192 to 199° F). The thermostat will also automatically reach wide open so it will not restrict flow to the radiator as the temperature of the coolant rises in hot weather to around 104° C (220° F). Above this temperature the coolant temperature is controlled by the radiator, fan, and ambient temperature, not the thermostat.

The thermostat is operated by a wax filled chamber (pellet) which is sealed. When coolant reaches a predetermined temperature, the wax expands enough to overcome the closing spring and water pump pressure, which forces the thermostat to open. Coolant leakage into the wax pellet will cause a thermostat to fail in the open position. Do not attempt to free-up a stuck open thermostat.

If the thermostat is stuck open or allows coolant leakage through it, the engine will not operate at the proper temperature for obtaining engine fuel efficiency, performance and emissions levels. If this condition occurs, a diagnostic trouble code will be set and a MIL light will be turned on.