What Causes the Abnormal Noise After the Car Is Turned Off?
3 Answers
The causes of abnormal noise after the car is turned off include the cooling sound of the catalytic converter, the cooling sound of the exhaust pipe, and uneven cooling of the engine. The details are as follows: Uneven Cooling of the Engine: After driving for a period of time, the engine temperature becomes very high. When the car is turned off, the temperature of each component decreases, and thermal expansion and contraction cannot occur uniformly. This inevitably leads to friction between the internal metal parts of the engine due to cooling contraction, resulting in abnormal noise. Cooling Sound of the Exhaust Pipe: Generally, the temperature of the exhaust pipe during cold idle is around 200 degrees Celsius. When the car is under high load or there is combustion of the air-fuel mixture in the exhaust pipe, the temperature can be even higher. Therefore, the exhaust pipe will also produce abnormal noise due to thermal expansion and contraction. Cooling Sound of the Catalytic Converter: The normal operating temperature of the catalytic converter is between 400-800 degrees Celsius. After the car is turned off, its operation gradually stops, and the temperature decreases. The internal metal parts undergo thermal expansion and contraction, leading to abnormal noise.
I'm quite familiar with the strange noises after turning off the engine. As a car owner with ten years of driving experience, I often hear those ticking or metal contraction sounds. The most common cause is the thermal expansion and contraction effect when the exhaust pipe or turbocharger cools down. Metal expands when heated and contracts when cooling after parking, producing those noises, especially noticeable after high-speed driving. Brake discs do the same thing – last time after driving on mountain roads, I heard slight noises from the brake area when parked, completely normal. Additionally, if the car has a turbo cooling fan, it may continue running for a while to dissipate heat, causing extra noises. However, if the sound is too loud or accompanied by creaking noises, it might indicate loose parts or issues with certain engine components – I'd recommend checking the exhaust system connection points. Most of these situations are harmless, but regular cleaning of brake discs can reduce noise and maintain stability.
I think the issue of abnormal noises is mostly the vehicle 'catching its breath.' Based on my years of driving experience, the sounds after turning off the engine sound like metal saying, 'I finally get to rest.' The main culprits are the exhaust pipe and engine components cooling and contracting, especially noticeable in turbocharged cars. The other day after a long drive, I could clearly distinguish those slight ticking sounds. Brake discs also often make noises after cooling down, which is a natural physical phenomenon. In rare cases, it's a side effect of the carbon canister cleaning process, producing some bubbling sounds. It's no big deal unless the sound suddenly becomes sharp or lasts for a long time, then it's worth checking at the shop. Routine maintenance, like checking the tightness of exhaust suspension bolts, can prevent issues. The key is not to panic over it—safe driving comes first.
