Thermostat
A temperature-sensitive valve that regulates the flow of coolant between the engine and the radiator to maintain optimal operating temperature.
The engine thermostat is a small but critical valve in the cooling system located between the engine block and the radiator. Its primary function is to regulate the flow of engine coolant to maintain the engine's optimal operating temperature (typically between 195 and 220 degrees Fahrenheit).
When the engine is cold, the thermostat remains closed, forcing coolant to circulate only within the engine block. This allows the engine to warm up quickly to its efficient operating temperature, reducing wear and emissions. Once the coolant reaches a set temperature, a wax pellet inside the thermostat expands, opening the valve and allowing hot coolant to flow to the radiator to be cooled.
Thermostats typically fail in one of two ways: stuck open or stuck closed. If a thermostat is stuck open, the engine will run too cold, resulting in poor cabin heater performance, increased fuel consumption, and higher emissions. If a thermostat is stuck closed, coolant cannot flow to the radiator, leading to rapid engine overheating, which can cause severe damage like cracked cylinder heads or a blown head gasket.
Replacing a thermostat is a relatively inexpensive preventive maintenance procedure that is often performed during a water pump replacement or coolant flush service.