The unit coolant level is too low (it should be visible from the oil sight glass at this time, but not more than half of it); The oil cooler is dirty. How to judge whether the cooler is dirty depends on the temperature difference between the oil inlet temperature and the oil outlet temperature. The normal temperature should be between 20-30 ℃. If the external dust blocks the heat dissipating gas, you only need to use compressed air to clean it. If it can't be blown off and the radiator is dirty, you need to use professional cleaning agent to clean it, (if heavy oil cleaning agent, such as acetone, dust, etc.) if the internal blockage of the radiator is serious, it needs to be used. Clean water pump is used for circulating cleaning, and the cleaning time is defined according to the situation. If the water-cooled radiator is blocked, the best way is to remove the front and rear end covers and clean the inside of the copper tube; The oil filter is blocked; Failure or damage of temperature control valve; The oil cut-off valve is not energized, or the coil is damaged, or the diaphragm of the solenoid valve is aging or broken. The oil cut-off valve usually appears in the old machine, and the cooling fan motor fails; The exhaust pipe is not smooth or the exhaust air has resistance and the resistance is relatively large; If the ambient temperature is too high, the exhaust temperature of the air compressor unit will be too high.