The air bubbles in the diesel engine tank are generally caused by high-pressure gas in the air cylinder that enters the cooling water channel. The cause of helium and its remedy are as follows: The cylinder head nut is not tightened according to the specified torque. If the torque is too small, the cylinder head is not compressed and high-pressure gas will enter the water channel. Tighten the cylinder head nuts at the specified torque and retighten them regularly. The cylinder head gasket is used for a long time and it is damaged or burned, and the sealing performance is deteriorated, resulting in air leakage. Replace the new cylinder head gasket. The cylinder head is not flat or deformed, resulting in air leakage. Grind the cylinder head plane or replace the cylinder head. Improper assembly, resulting in broken cylinder sleeve shoulder and gas. Change the cylinder liner according to the prescribed method. The cylinder sleeve shoulder height is not enough or the depth of the body shoulder hole is too large, resulting in the cylinder into the body, the plane height of the protruding body is not enough, or even subsidence, gas will break into the water channel from the shoulder. Therefore, test the assembly before assembly, check the amount of protrusion, and ensure that it is within the allowable range.