Passat leads the warm air to drop in water temperature.

Passat leads the heater to turn on, and the water temperature drops. Check the thermostat. First check whether the engine water temperature is normal. If it has been in a low temperature state and does not reach the working temperature, the warm air will definitely not be hot. At this time, we can focus on whether the thermostat has been in a large cycle state, or whether the signal of the water temperature sensor is true, and repair or replace the faulty factory. Focus on whether there is a large temperature difference between the inlet and outlet pipes in front of the warm air box. If this happens, the heater box must be blocked and needs to be disassembled, cleaned or replaced. It depends on whether the flow rate and temperature of coolant entering the warm air tank meet the requirements. The temperature can be measured by infrared thermometer, and the flow can be judged comprehensively through the diagnostic data and fault storage of the detector. The common causes are pump loss and damage, and the heater flow valve and coolant circulation valve are damaged.