Replacing car thermostats Replacing car thermostats Thermostats in cars are often neglected, if not totally forgotten, units. Yet they play an important role in the general performance of cars by restricting water flow until the engine has warmed-up.
Thermostats are heat sensitive valves that open and close.
On cars they prevent ciculation of coolant to the radiator until the engine is warm enough. When the thermostat is closed water only flows through the water pump and water jacket to let the engine warm quickly. When the thermostat opens, water can then pass through the radiator for general cooling. Having a car that warms quickly is particularly useful in cold weather when you want to use your car heater as soon as plossible. The thermostat is in a small housing positioned where the top radiator hose connects to the engine.