In a liquid cooled engine, the thermostat is a valve installed between the water pump and the radiator. It controls when the radiator starts to cool the engine. It’s job is to help the engine reach operating temperature quickly.
How does it work?
A cylinder in the thermostat is filled with a special wax. A rod is set in the wax and attached to the valve.
- As the wax heats up, it melts and expands.
- This forces the rod to move and open the valve.
- As the wax cools, it contracts.
- Spring pressure moves the rod back and closes the valve.
When the engine is cool, the thermostat is closed. It blocks flow to the radiator so coolant only circulates through the engine.
When the coolant reaches the melting point of the wax, the thermostat starts to open. This is known as the “opening temperature” of the thermostat.
This process continues as the engine is running. The thermostat opens and closes, based on the temperature of the coolant.
How does it affect performance?
It’s a common belief that the thermostat controls the operating temperature of the engine. This is only partly true. The thermostat sets the bottom of the operating range. The top of the operating range depends on the combined cooling capacity of the radiator and fan(s).
Engines are designed to run most efficiently within a certain temperature range. Usually, this is somewhere between 180-200 degrees. The thermostat really prevents “over-cooling.” This means the engine warms up faster and stays warm.
Most engine wear occurs when it’s cold. Without a thermostat, it would take a long time for the engine to reach operating temperature. This would cause excessive wear to bearings and other moving parts.