The radiator hood has a pressure valve that is pressurized to the coolant. The coolant temperature under pressure rises to more than 100 ℃, which makes the difference between coolant temperature and air temperature greater. This can improve the cooling effect. When the radiator pressure increases, the pressure valve opens and the coolant is returned to the tank mouth, and when the radiator is decompressed, the vacuum valve opens, allowing the tank to release the coolant. Pressure drop (cooling) during pressure rise (high temperature) during stress reduction during pressure increase.