What Causes the Abnormal Noise After a Car Shuts Off?
2 Answers
Car shutting off with abnormal noise reasons are as follows: 1. Cooling sound of the three-way catalytic converter: The normal operating temperature of the three-way catalytic converter is 400-800°C. After shutting off, its operation gradually stops, and the temperature decreases, causing the internal metal components to expand and contract with heat, resulting in abnormal noise. 2. Cooling sound of the exhaust pipe: Generally, during cold idle, the exhaust pipe can reach a temperature of over 200°C. When the car is under high load or there is a mixture burning in the exhaust pipe, the temperature can be even higher. Therefore, the exhaust pipe also expands and contracts with heat, producing abnormal noise, often originating from the front end of the exhaust pipe and the flexible connection. 3. Cooling sound of the turbocharger: Under normal conditions, the exhaust gas temperature reaches 600-700°C, accelerating the turbocharger's rapid rotation and friction-generated heat. After shutting off, the heat expansion and contraction are very noticeable, leading to abnormal noise.
Oh, I've also experienced strange noises after the car stalls, it feels like the car is sighing! The most common reason is thermal contraction. When the car is turned off after running hot, metal parts like the exhaust pipe and engine casing start cooling and shrinking, making clicking sounds, just like a hot pan cooling down—natural and harmless. Also, the cooling fan might still be running; if the engine overheats, it will automatically continue to blow air to dissipate heat, producing a whooshing noise that stops after a while. Additionally, fluid systems like coolant or engine oil flowing back in the pipes can cause slight gurgling sounds, which don’t affect safety. If the noise is small and brief, it’s generally fine; but if it’s particularly loud or accompanied by harsh friction, you should check for loose or worn parts, especially in older cars that need timely maintenance. After driving, don’t rush to turn off the car—let it rest quietly for a few minutes to reduce such noises. In short, understanding these small details can make your driving experience more reassuring!
