The case comes from a professional repair shop: a BMW five-series car, only to find that the coolant in the expansion kettle is almost gone when the engine cover is opened. The key is that the owner only maintains the car, and the coolant has been changed in recent months. The mechanic first checks the engine compartment to see if there is any coolant leakage in the engine compartment. In order to see the specific location of the leaked coolant, the air cleaner housing was removed. Soon, the master found that the warm water valve was leaking coolant. The main function of the warm air water valve is to control the automobile warm air system, which is mainly used in cold weather. According to the master's experience, the biggest possibility is that the warm air water valve has quality problems and leaks coolant.