Why does the engine still make noise after the car is turned off?
1 Answers
The reason the engine still makes noise after the car is turned off is that the engine cooling system is still working. To prevent the engine or turbocharger from overheating, vehicles are equipped with a delayed cooling function. This function operates based on the water temperature measured by sensors and will continue working until the water temperature drops within the set range. Reasons for abnormal noises from the engine when turning off the car include: 1. Cooling noise from the three-way catalytic converter: The normal operating temperature of the three-way catalytic converter is 400-800°C. After turning off the engine, its operation gradually stops, and the temperature decreases, causing the internal metal components to expand and contract, resulting in abnormal noises. 2. Cooling noise from the exhaust pipe: Typically, the exhaust pipe can reach a temperature of over 200°C during cold idle. If the vehicle is under high load or if there is combustion of the air-fuel mixture in the exhaust pipe, the temperature can be even higher, leading to thermal expansion and contraction of the exhaust pipe and causing abnormal noises. 3. Water pump noise: Water pump noise is mainly caused by the pump wheel bearing of the water pump. Due to prolonged operation, erosion by coolant, and scale buildup, the water pump blade bearing can become severely worn. If the issue is not addressed for a long time, it can lead to complete failure of the water pump, where the pump operates but fails to circulate coolant, thereby affecting engine cooling.
