The thermostat automatically adjusts the amount of water entering the radiator according to the temperature of the cooling water, changes the circulation range of the water to adjust the cooling capacity of the cooling system, and ensures that the engine is working in the proper temperature range. The thermostat must maintain a good technical condition, otherwise it will seriously affect the normal operation of the engine. Such as the thermostat main valve opened too late, it will cause the engine overheating; main valve open too early, then make the engine warm-up time, so that the engine temperature is too low.