What Is A Cooling System Thermostat?

A thermostat regulates the amount of coolant flowing through an engine to maintain a certain temperature. The thermostat can usually be found, under the bonnet, between the engine and the radiator. When the car starts to run, the thermostat blocks all coolant, so the engine can quickly get up to an optimum temperature (200℉, 95℃). This temperature helps the car to run smoothly. If the engine temperature rose more gradually, the engine would wear out faster and there would be more toxic emissions.

As the engine gets hotter, a lot of the lubricating oil dries out. The heat will trigger mechanisms inside the thermostat, be they electrical or even wax based. The thermostat opens the path for coolant to run through the engine, cooling and lubricating it. The thermostat will then close again once the engine reaches its optimum temperature. If you’re interested in understanding better how the part works it’s worth buying one from a car parts store just to see it work as if by magic in a cup of boiling water.

Like all bits of a car, the thermostat can fail and unless you have an infrared heat gun lying around it can be hard to spot. The thermostat in extreme conditions can seize up. In hot conditions, this can mean the engine takes a long time to warm up so you release more pollutants. In cold conditions, it can cause your engine to overheat as it has no access to coolant. In both cases it is best to replace the thermostat as soon as possible to prevent damage to the engine.