Your engine coolant thermostat sits between the engine and the radiator, in a thermostat housing. The thermostat blocks the flow of coolant to the radiator until the engine has warmed up. Once the engine is warm enough, usually around 200-220 degrees F, the thermostat opens and allows the coolant to flow. The engine coolant thermostat is the most common component of the cooling system to fail, which can cause your car to overheat in the unlikely event it were to be stuck closed. More commonly, the thermostat can be stuck open, making it difficult for your engine to warm up. This can result in your car running cool, causing an overly rich fuel mixture and an inefficient running engine. It should be replaced anytime you have major work done to the coolant system.
