A Honda accord car with a mileage of about 100 thousand km and a F22B4 engine. User reflection: the car is overheated by the engine. In addition, the vehicle also has the phenomenon of accelerating weakness, exhaust pipe noise and so on. After receiving the car: check the coolant, found that the coolant capacity is insufficient, the cooling fluid in the radiator is milky white, indicating that the coolant mixed with oil. No leakage was found in coolant pipes and interfaces. When the oil dipstick is pulled out, it can be seen that the oil has been diluted by the coolant and contains blisters. It is obvious that coolant enters the cylinder, which is usually caused by damage to the cylinder gasket. Remove the cylinder head for inspection. The cylinder gasket (metal material) has no obvious damage marks. The flatness of cylinder block and cylinder head is measured within the standard range of 0.05 mm. Check the joint face of cylinder head and cylinder block, and no traces of coolant entering the cylinder are found. The inner wall of the cylinder is smooth, and there is no abnormal wear or crack. Checking the combustion chamber of the cylinder head reveals that the color of the 3 cylinder spark plug and valve is whitish, which is obviously different from that of the other cylinders. Remove the spark plug and find that there is a serious corrosion at the outlet of the cylinder head. In order to judge the leakage of the cylinder head, clean up the carbon of the cylinder head, check it carefully, and find that there is a sand hole at the inlet of the 3 cylinder combustor. It seems that the coolant flows into the fuel chamber by this way. Replace the cylinder head, and the failure is completely eliminated. The engine adopts a wet cylinder liner, which is filled with coolant around the cylinder wall. The cylinder head is made of aluminum and is easy to corrode or damage. In the maintenance work, do not use the disqualified coolant, otherwise the cooling fluid pipeline will be blocked, the cylinder head, the radiator, the cylinder body and other components are corroded, and the engine has serious mechanical failure.