Thermostat is a kind of automatic temperature control device, usually contains temperature sensing components, by expansion or contraction to open, turn off the flow of coolant, that is, according to the temperature of the cooling liquid automatically adjust the water into the radiator, change the coolant circulation range, to adjust the cooling system's cooling capacity. The thermostat used by the engine is mainly a wax thermostat, which is controlled by the paraffin wax inside the coolant circulation through the principle of thermal expansion and cold contraction