What Causes Abnormal Engine Noise When Shutting Off?

[SanJackson]

The reasons for abnormal engine noise when shutting off are as follows: 1. Cooling noise from the catalytic converter: The normal operating temperature of the 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, resulting in abnormal noise. 2. Cooling noise from the exhaust pipe: Typically, the exhaust pipe can reach temperatures above 200°C during cold idle. Under high vehicle load or when mixed gas burns in the exhaust pipe, the temperature can be even higher. Thus, the exhaust pipe also expands and contracts, producing abnormal noise, often originating from the front end or flexible joint of the exhaust pipe. 3. Water pump noise: Water pump noise is mainly caused by the pump wheel bearing. Prolonged operation, exposure to coolant erosion, and scale buildup lead to severe wear of the water pump blade bearings. If not addressed promptly, this can cause complete failure of the water pump, rendering it ineffective in circulating engine coolant and thereby affecting engine cooling.