Failure phenomenon: the Honda accord is 79000 kilometers in mileage. When the car is used again for one year, the engine work state is very poor, there are different noises, the speed is not smooth, the work is less than 20min, the water temperature reaches 110 degrees C, the water tank is open. Fault diagnosis: check the cooling system, water tank and water pipe are normal, the coolant is dirty, the new coolant is replaced, the cold car starts, the cooling fluid is well circulate, the engine works 15min, the water temperature is normal, the electronic fan works well, the high and low speed electronic fans can work normally. Engine continues to work, water temperature continues to rise, about 25min, the water tank boil. It is doubted that the pump or the thermostat has problems, and dismantling the water pump inspection, found that the pump has no abnormal, dismantle the thermostat, so that the cooling system has been in a large circulation state, starting the engine test, the failure is still. Check engine oil with no signs of water penetration, but oil is thin and black. Because of the serious noise of the car, the engine must be removed. After the engine was disintegrated, it was found that the crankshaft was seriously injured, exceeding the limit of repair. The crankshaft bearing and connecting rod bearing are also badly pulled. The owner asked for a new engine to replace, and the engine remained high after the replacement. After careful consideration, it is doubted that the muffler is wrong. Vibrate the muffler with the hand, and hear the sound. Because the car has been stopped for a year, the internal corrosion is serious, rust is broken into particles, the outlet of the exhaust pipe is blocked, the engine exhaust is not smooth, the temperature is constantly rising, the engine oil is deteriorated and the dust particles are formed, which makes the oil not only not lubricate, but aggravates the wear, so the engine is seriously damaged. Troubleshooting: replace muffler, troubleshooting.