Why does the car's exhaust pipe turn red?
3 Answers
Car exhaust pipes turning red occur because some of the fuel mixture from the cylinders continues to burn inside the exhaust pipe. If the air-fuel mixture is too lean, the combustion speed of the flammable gas slows down, extending into the exhaust stroke and causing the exhaust pipe to turn red. Below are the specific reasons: 1. Burning gases rushing into the exhaust pipe raise the exhaust temperature. This can happen due to poor sealing of the exhaust valve or excessively small valve clearance, allowing burning gases to enter the exhaust pipe and increase its temperature. Delayed fuel injection not only slows combustion but also leads to incomplete combustion, causing diesel to burn in the exhaust pipe during later stages of injection, further raising the exhaust temperature. 2. During maintenance, adjust the air-fuel mixture concentration, inspect and adjust valve clearance, and fine-tune ignition or injection timing. Remove the exhaust pipe and muffler, disassemble the muffler, and clean carbon deposits by soaking in kerosene (or using chemical methods), scraping with a blade, or burning the muffler core over an open flame to dry it out. Finally, clean with a wire brush. Replace any worn or damaged components as necessary for repair.
I've encountered the situation of a glowing red exhaust pipe several times, especially once while cruising on the highway. Seeing the red glow flashing in the rearview mirror was quite frightening. Later, I learned that this is usually caused by the engine's air-fuel ratio being too lean, meaning the system injects too little fuel and too much air, causing the combustion temperature to soar to very high levels. Ignition timing that's too late can also cause the flame to continue burning during the exhaust stroke, turning the entire exhaust pipe red-hot. This is more common during prolonged high-speed driving or heavy downhill loads, especially in turbocharged cars, where heat accumulates very quickly. When checking, first use an infrared thermometer to measure the temperature—don't touch it with your hands, as the high temperature can easily cause burns or ignite nearby oil stains. While driving normally, avoid excessive coasting or frequent rapid acceleration, and keep an eye on the dashboard temperature gauge. Prevention is simple and effective.
As someone who frequently works on cars, I believe the root cause of a glowing exhaust pipe is often related to the combustion system. A lean air-fuel mixture leads to incomplete combustion, and the exhaust gases continue to react thermally in the exhaust pipe, causing the temperature to rise. Delayed ignition timing is another common factor—if the spark plug fires too late, the flame hasn't extinguished by the time the piston moves downward. A clogged catalytic converter can trap gases and heat inside, while accumulated dust in the exhaust muffler may also cause blockages. The solution is to park the car and use a diagnostic tool to check for error codes or inspect the oxygen sensor readings for abnormalities. It's best to regularly clean the air filter and fuel injectors to maintain the proper fuel supply ratio, which saves money and avoids major issues.
