What Causes the Ticking Sound After a Car Engine Shuts Off?

[Mateo]

It is due to the thermal expansion and contraction of the engine, which is normal and nothing to worry about. Here are the details: 1. Working Principle: When the engine is running, the temperature varies in different parts. The cylinder block temperature generally does not exceed 100°C, while the exhaust pipe can reach 400~500°C, and the catalytic converter can even reach up to 600°C. Therefore, the expansion rates of these parts differ. After the engine stops, under the influence of ambient temperature, it gradually cools down. During this process, the high-temperature exhaust pipe and catalytic converter cool faster and deform more significantly, while the cylinder block cools slightly slower. Due to the inconsistent deformation, friction occurs at the connection points, resulting in a "ticking" sound. 2. Exhaust Pipe Cooling Sound: Typically, during cold idle, the exhaust pipe can reach temperatures above 200°C. Under high load or when unburned mixture ignites in the exhaust pipe, the temperature can be even higher. Thus, the exhaust pipe also undergoes thermal expansion and contraction, producing unusual sounds. In many cases, this sound originates from the front end of the exhaust pipe or the flexible joint.