What Causes Abnormal Noises in the Engine Compartment After the Vehicle Shuts Down?
2 Answers
There are several reasons for abnormal noises in the engine compartment after the vehicle shuts down: Cold Start Noise: When 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. As a result, the valves do not receive sufficient lubrication, and the hydraulic lifters and mechanical rocker arms fail to operate properly, leading to abnormal noises. Inappropriate Engine Oil: If the engine oil viscosity is too high, it can cause insufficient lubrication during engine operation, resulting in friction and abnormal noises. Many car owners experience this issue after changing to a different type of oil during maintenance. Incorrect Belt Tension: If the belt tension is insufficient, it can produce a sharp squeaking noise, which sounds particularly unpleasant.
I've been repairing cars for over a decade, and it's very common to hear strange noises from the engine compartment after turning off the ignition. The most common sound is the catalytic converter in the exhaust pipe cooling down—metal contracting can produce a cracking noise, similar to the sound of pouring water on red-hot metal. It could also be the sound of the turbocharger's blades coming to a stop; cars with turbos often make this noise. If you hear a bubbling sound like boiling water, don't panic—that's just the coolant circulating through the cooling pipes. It's also normal for the fan to suddenly start running; if the engine is too hot, it will automatically cool down for a few minutes. However, if you hear a particularly harsh metal grinding noise, it's best to check if the exhaust pipe hanger is loose. Most of these sounds are harmless—just relax in the car, listen to some music, and wait for them to stop.
