The main function of the cooling system is to maintain the engine's precise working temperature. This system is comprised of many components including the thermostat. With its main function to regulate your car's cooling system, the thermostat is able to carry out its critical function by controlling the amount of water or liquid coolant that is pumped through your vehicle's radiator. When the engine is already cool, the thermostat restricts the flow of water. Conversely, when the engine is too hot, the opening of the coolant control valve opens in order to allow the entry of water into the radiator.