What Causes Abnormal Noises in the Engine Compartment After the Vehicle Shuts Off?

[LaEverly]

There are several reasons for abnormal noises in the engine compartment after the vehicle shuts off: 1. Cold start noise: After the car has been parked for a long time, the engine oil flows back to the oil pan. During a cold start, the oil pump cannot immediately build up oil pressure, especially in the upper part of the engine. The valves do not receive sufficient lubrication, and the hydraulic lifters and mechanical rocker arms fail to operate properly, resulting in abnormal noises. 2. Incorrect engine oil: If the oil viscosity is too high, it can lead to insufficient lubrication during engine operation, causing friction and abnormal noises. Many car owners experience this issue after changing to a different type of oil during maintenance. 3. Improper belt tension: If the belt tension is insufficient, it can produce a sharp squealing noise, which is particularly unpleasant to hear. 4. Engine 'backfire' fault: When there is excessive carbon buildup on the engine valves or incorrect timing adjustment, the engine may produce a 'popping' sound. 5. Poor fuel quality or incorrect octane rating: Using low-quality fuel or fuel with an inappropriate octane rating can worsen combustion inside the engine, causing severe vibrations and noise. 6. External engine-related noises: If the engine mounts or interconnected external components become loose, they can also cause abnormal noises.