Inspection and analysis: the maintenance personnel, in line with the idea of simplicity and complexity, first check the lines, moving parts and tie lines related to the water temperature change, and find no problems. Under the idle condition, the "magneto magnetic" noise of the pump is heard, and the sound of "mouth Magnets" is similar to that of the double top camshaft engine carried by the car, not listening carefully, it is difficult to distinguish between the sound of the pump or the noise of the engine. As the temperature of the engine rises and the noise of the electronic fan increases, it seems that the sound is not heard again. Then, using a long screwdriver to contact the outside of the suspect pump carefully, it was found that the noise inside the pump was obvious. Dismantling the pump, found that the pump blade and pump shaft loose. The temperature of the coolant is too high and low, and the water temperature meter pointer shows a big change. The reason is that with the engine running at different speeds, sometimes the pump impeller and the pump shaft are loose and can synchronize with the flow centrifugal force to reach 120~140 kPa of the standard water pressure of the cooling fluid. On the other hand, it can not operate synchronously, which leads to the rise of water temperature caused by the decrease of the circulating pressure of the coolant, and the water temperature change directly to the water temperature sensor, and the electrical signal of the water temperature sensor is then transferred to the water temperature meter pointer. Troubleshooting: replace the pump, thoroughly troubleshooting the trial run.