What does a thermostat control?

Answer 1

On an automobile (as opposed to a thermostat on a boiler in a home or building), the THERMOSTAT opens and closes to allow or stop the flow of coolant (anti-freeze) from circulating through the "cooling system" (hoses, water pump, Radiator, engine, Coolant reservoir, etc.) as well as the "heating system" also called "climate control system" (heater core). By closing and thereby stopping the flow of coolant, the heat generated by the running of the engine is trapped causing the engine to warm up rapidly. Useful in warming up an engine that hasn't been driven in a while, in cold weather and/or for transferring heat to the climate control system that warms up the interior passenger compartment in cold weather. When the THERMOSTAT is in the open position, coolant is allowed to flow to the radiator which "radiates" or gives off the heat that the coolant acquired as it flowed through the boiling hot engine block. As it travels the long serpentine route through the Radiator, air passing through the grille in the front of the car as the car moves forward or sucked in by the rotating fan cools the coolant. The coolant, pushed by the water pump, then recirculates back to the engine and begins the heat exchange of the cooling process all over again.

Why not have the coolant constantly flowing and eliminate the THERMOSTAT altogether? Imagine your engine is like a Marathon Runner. When he starts the race his muscles are cold and he needs to warm up before the race and so he doesn't want to be sprayed by cold water at that point, especially if the race is being run on a cold day. However, if it is already a very hot day or after he has begun to get hot from running a while, he will appreciate, even need a cold drink or spray of cold water on him to cool him down. The THERMOSTAT turns the waterworks on and off at the right time and situation.