1. Air leakage from under the piston rings. 2. Water has entered the oil, diluted and spoiled oil, or the oil level is too high or low. 3. The support bearing is clamped too tightly. 4. The water pump is broken or loose. 5. The thermostat does not work, or there is not enough fluid in the expansion tank. 6. The main head gasket is damaged. 7. There is too much scale in the engine water jacket. 8. Engine overloaded. 9. Advance angle is too large.
1. Replace with new ones. 2. Check and change the oil or correct the oil level by draining or adding the required amount. 3. Check and adjust. 4. Check and adjust. 5. Replace the thermostat and add water. 6. Replace with a new one. 7. Clean the water jacket. 8. Reduce the load. 9. Check and adjust