Thermostats, Control The Stop And Go Of Engine Coolant.
Its job is to block the flow of coolant to the radiator until the engine has warmed up.
When the engine is cold, no coolant flows through the engine. Once the engine reaches its operating temperature (generally about 200 degrees F, 95 degrees C), the thermostat opens. By letting the engine warm up as quickly as possible, the thermostat reduces engine wear, deposits and emissions.