First, the water tank is short of liquid, that is, the antifreeze is insufficient. The reason may be that the cooling system leaks liquid and the air in the original car is not completely exhausted.
Second, the circulation of the central control small water tank is not smooth. The reasons may be air resistance, impurity blockage, damage of thermostat in small water tank (only some models have secondary thermostat) and so on.
Third, the problem of water tank circulation system. It may be that the water pump is damaged. , need further inspection and confirmation.