What Causes the Noise After the Car Engine Stops?
2 Answers
There are both normal and abnormal reasons for the noise after the car engine stops. Normal reasons: 1. Cooling sound of the catalytic converter: The normal working temperature of the catalytic converter is between 400 to 800 degrees. After turning off the engine, its operation gradually stops, and the temperature drops, causing the internal metal parts to expand and contract, resulting in noise. 2. Cooling sound of the exhaust pipe: During cold idle, the exhaust pipe also expands and contracts due to heat, producing noise. 3. Cooling sound of the turbo: Normally, the exhaust gas temperature reaches 600 to 700 degrees, accelerating the friction-generated heat from the turbo's rapid rotation. After turning off the engine, the heat expansion and contraction are quite noticeable, leading to noise. Abnormal reasons may include loose screws at the catalytic converter interface, damaged carbon canister solenoid valve, or poor operation of the starter motor.
It's normal to notice some noises after the engine stops, mainly due to thermal expansion and contraction—metal components like the exhaust pipe and catalytic converter often make ticking sounds as they cool down after high-temperature operation. The fan might also keep running for a while to help the cooling system dissipate heat, which is more common in summer. Additionally, if the water pump or bearings are worn or aged, they may produce a continuous humming sound after shutdown, requiring prompt inspection to avoid affecting the engine's lifespan. Generally, brief and mild noises are nothing to worry about, but if the sound is persistent, intense, or accompanied by vibration, it's best to visit a professional repair shop. Don’t let minor issues escalate—after all, driving safety comes first.
