Thermostat: Description and Operation

A wax pellet-type thermostat is used to control the flow of coolant through the cooling system. Mounted in the thermostat housing on the back of the cylinder head, the thermostat stops the flow of coolant from the engine to the radiator to provide faster warm up and regulate coolant temperature. The wax pellet is hermetically sealed in a metal case. The wax element expands when heated and contracts when cooled. As the vehicle is driven and the engine warms up, the coolant temperature increases. When the coolant reaches a specified temperature, the wax pellet element expands and exerts pressure against a metal case, forcing the valve open. This allows coolant to flow through the system and cool the engine. As the pellet cools, the contraction allows a spring to close the valve. In the top portion of the thermostat an air bleed hole is provided to vent any gas or air which may have penetrated the cooling system. The thermostat is an 88° C (190° F) thermostat. The temperature at which the thermostat begins to open is stamped on the thermostat.