What Does a Thermostat Do? The thermostat is a small valve that regulates the temperature in the engine by controlling coolant flow. If the engine is cold, the valve stays closed to let it warm up. However, as the engine warms up, the thermostat slowly opens, enabling coolant to flow through the radiator. This process enables the engine to remain at a safe operating temperature. What Are the Signs of a Failing Thermostat? Overheating (or overcooling) Coolant leaking Erratic temperature changes Strange sounds Heater problems How to Replace a Thermostat in a Car Part 1 Removing the Old Thermostat .
