1, the lid of the expansion kettle failed, and the aging of the seal accelerated the escape speed of water vapor;
2. The lid of the expansion kettle fails and the pressure valve fails, which leads to the accelerated escape speed of water vapor;
3. There is slight leakage in the cooling system. Check the radiator, radiator inlet pipe, outlet pipe, water pump outlet pipe and other cooling system connection parts for slight leakage.
4. Add water instead of antifreeze and antirust liquid. The boiling point of ordinary water is 100℃, and the antifreeze and antirust liquid can withstand above 120℃. If it is not a regular coolant, then water is really easy to be less.