Thermostat: Description and Operation

DESCRIPTION - 2.7L

Fig. 20 Thermostat and Housing - 2.7L:

The thermostat is located on the lower left side of engine, near the front. The thermostat is on the inlet side of the water pump. It has an air bleed located in the thermostat flange. The air bleed allows internal trapped air during cooling system filling to be released.

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 - 93 °C (192 - 199 °F). The thermostat also will automatically reach wide open so it will not restrict flow to the radiator as 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 container (pellet) which is sealed. When heated coolant reaches a predetermined temperature, the wax expands enough to overcome the closing spring and water pump pressure, which forces the valve to open.