Thermostat Description

The thermostat is a coolant flow control component that utilizes a temperature sensitive wax-pellet element.
The lower end of the thermostat, containing the wax-pellet element, is installed in the engine water jacket.
The thermostat performs the following functions:
- Controls the flow of coolant to the radiator
- Promotes coolant flow through the engine block
- Enables a controlled engine warm-up
- Maintains a minimum operating coolant temperature





The wax pellet element (4) in the thermostat expands when heated, and contracts when cooled.
The element connects through a piston (1) to a thermostat valve (2).
When the element is heated, pressure is exerted against a rubber diaphragm (3) which forces the thermostat valve to open. As the element is cooled, the contraction allows a spring (5) to close the thermostat valve.
When the coolant temperature is below the rated thermostat opening temperature, the thermostat valve remains closed. This prevents circulation of coolant to the radiator and allows the engine to warm quickly.
After the coolant temperature reaches the rated thermostat opening temperature, the thermostat will open, allowing the coolant to circulate to the radiator where the engine heat is dissipated to the atmosphere.
The thermostat also provides a restriction for the cooling system, even after the thermostat has opened. The pressure difference, created by the restriction, prevents cavitation at the water pump and forces coolant to circulate through the engine block.