What causes the abnormal noise in the Mercedes-Benz E300L?

[KylieFitz]

Reasons for abnormal noise in the Mercedes-Benz E300L: Uneven engine cooling: After driving for a period, the engine temperature becomes very high. When the engine is turned off, the temperature of various components decreases, and thermal expansion and contraction cannot occur uniformly. This inevitably leads to gaps between internal metal parts due to cooling contraction, resulting in friction and abnormal noise. Cooling noise from the exhaust pipe: Generally, the temperature of the exhaust pipe during cold idle is around 200 degrees Celsius. Under high load or when the mixture burns in the exhaust pipe, the temperature can be even higher. Therefore, the exhaust pipe also undergoes thermal expansion and contraction, producing abnormal noise. Cooling noise from the three-way catalytic converter: The normal operating temperature of the three-way catalytic converter is between 400-800 degrees Celsius. After the engine is turned off, its operation gradually stops, and the temperature decreases. The internal metal parts then undergo thermal expansion and contraction, leading to abnormal noise.