What Causes the Squeaking Sound When the Car Shuts Off?
2 Answers
In most cases, abnormal noises after the engine shuts off are normal, but they could also indicate damaged car components. Normal causes of abnormal noises: Cooling sound of the catalytic converter: The normal operating temperature of a catalytic converter ranges between 400-800°C. After shutdown, its operation gradually stops, and the temperature drops, causing the internal metal components to expand and contract due to heat, resulting in abnormal noises. Cooling sound of the exhaust pipe: During cold idle, the exhaust pipe can reach temperatures above 200°C. Under high load or when unburned fuel mixture ignites in the exhaust pipe, the temperature rises even higher, leading to thermal expansion and contraction, which produces noises, often originating from the front end or flexible joint of the exhaust pipe. Turbo cooling sound: Under normal conditions, exhaust gases can reach temperatures of 600-700°C, accelerating turbo rotation and friction-induced heat. After shutdown, thermal expansion and contraction become pronounced, causing noises. Engine cooling imbalance: After driving, the engine temperature is high. Upon shutdown, components cool at different rates, leading to friction between metal parts due to uneven contraction, resulting in abnormal noises. Fault-related causes: Loose screws at the catalytic converter joint: Thermal expansion and contraction after shutdown can amplify the noise. Damaged charcoal canister purge valve: May cause fuel tank deformation and noise. Faulty starter solenoid: The solenoid engages the starter gear with the engine flywheel. If it malfunctions, it may produce a "clattering" noise upon disengagement. Refrigerant line issues: For example, resonance between the AC low-pressure pipe and a specific engine RPM (usually low) can cause abnormal noises. Damaged parts should be replaced promptly.
I've driven various cars, and a squeaking sound upon shutdown is quite common. In my years of experience, it's mostly due to thermal expansion and contraction of the exhaust system—metal cooling and contracting naturally makes noise. If it's an occasional small sound, no need to panic; it's a normal physical phenomenon. But if it squeaks every time you shut down, you should pay attention—it could be fan blades rubbing when stopping or a loose belt. When the fan belt ages and lacks sufficient tension, the load change at shutdown causes noise. Over time, a broken belt can affect the alternator or air conditioning. Checking it yourself is simple: open the engine hood after shutdown and locate the sound source. If it's near the exhaust pipe, check if the bracket screws are loose; if it's near the fan, try adding some lubricant. Prevention is key—I recommend checking the belt and exhaust brackets every two years to save money and avoid major repairs.
