Why Does the Car Exhaust Pipe Turn Black?

2 Answers
LaElle
07/25/25 11:59am
Unburned oil vapor passing through the three-way catalytic converter may partially carbonize, leading to blackening. Below is relevant information about car exhaust pipes: 1. Causes of white smoke from the exhaust pipe: White smoke emitted from the exhaust pipe is water vapor. If the radiator coolant decreases: It indicates damage to the engine cooling water channel or cylinder gasket, causing coolant to enter the cylinder for combustion. If coolant is not lacking: It may be due to water entering the exhaust pipe for some reason (such as rain or car washing). White smoke from the exhaust pipe is absolutely abnormal. It's best to identify the cause; otherwise, long-term emission of water vapor from the exhaust pipe can cause corrosion, leading to premature rust and damage. 2. Causes of loud exhaust pipe noise: If the car's noise is very loud, the most likely reason is damage or aging corrosion of the exhaust pipe. If the exhaust pipe is found to be aged, it should be replaced immediately.
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JuniperLee
08/11/25 8:10pm
I've been working on cars for over 20 years, and blackened exhaust pipes are extremely common. It all boils down to incomplete fuel combustion in the engine. For example, during cold starts when the temperature hasn't risen sufficiently, if too much fuel is injected or there's insufficient air, combustion becomes incomplete, leading to carbon deposits accumulating at the exhaust pipe outlet. Frequent short-distance driving where the engine barely warms up before stopping accelerates carbon buildup. Over time, not only does the exhaust pipe turn black, but the exhaust may also develop a strong odor. Additionally, aging spark plugs or clogged air filters can also cause poor combustion. I recommend checking spark plugs for carbon deposits or trying higher quality fuel. If the problem persists, taking the car for a high-speed run can help clear out carbon deposits, which is also beneficial for the vehicle's overall health.
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