Why does the engine make noise after the car is turned off?
2 Answers
Reasons for engine noise after the car is turned off: 1. Cool-down noise from the catalytic converter: The normal operating temperature of the catalytic converter ranges from 400 to 800 degrees. After the engine is turned off, its operation gradually stops, and the temperature drops, causing the internal metal components to expand and contract due to heat, resulting in abnormal noises. 2. Turbocharger cooling noise: Under normal conditions, the exhaust gas temperature can reach up to 700 degrees, accelerating the friction-induced heat from the turbocharger's rapid rotation. After shutdown, the thermal expansion and contraction become very noticeable, leading to abnormal noises. 3. Uneven engine cooling: After driving for a while, the engine temperature becomes very high. When turned off, the temperature of various components drops, and the thermal expansion and contraction rates are not uniform, causing friction between internal metal parts due to cooling contraction, which produces abnormal noises. 4. Cooling fan operation: Because the water temperature and engine temperature remain high immediately after shutdown, the fan continues to operate for one to two minutes.
I've driven many cars and found that engine noises after turning off the ignition are mostly normal. The most common occurrence is the cooling fan continuing to run because the engine temperature is high, and the fan needs to operate for a while to help cool it down and prevent overheating damage to components. For turbocharged cars, there's also a cooling circulation system that runs for a few minutes after shutdown to cool the turbocharger. Another reason is the thermal expansion and contraction of metal parts, such as the popping sounds from the exhaust pipe as it cools. I've seen this during my time as a mechanic—if the noise is brief and mild, there's no need to worry at all. However, if it lasts for a long time or is unusually loud, like a sharp screeching sound, it could indicate a stuck fan motor or an electrical issue. I recommend paying attention to these sounds regularly and seeking professional inspection if any problems are detected to prevent minor issues from escalating. Additionally, cleaning the radiator grille and checking connection wires during maintenance can prevent many potential problems.
