What Causes the Exhaust Pipe to Turn Red?
2 Answers
Exhaust pipes turning red occur when part of the combustible gas from the cylinders enters the exhaust pipe and continues to burn. The specific reasons are as follows: Combustible gases rushing into the exhaust pipe: This leads to the exhaust gases entering the exhaust pipe, raising the exhaust temperature. If the fuel injection timing is too late, it not only slows down the combustion rate but also results in incomplete combustion, causing diesel to burn in the exhaust pipe during the later stages of injection, thereby increasing the exhaust temperature. Part of the combustible gas from the cylinders enters the exhaust pipe: An overly lean air-fuel mixture can cause slow combustion after ignition, extending into the exhaust stroke and continuing to burn. Exhaust valve leakage or insufficient valve clearance: If the exhaust valve does not seal properly or the valve clearance is too small, it allows combustion gases to enter the exhaust pipe, raising the exhaust pipe temperature.
I've been repairing cars for over ten years, and the issue of a glowing red exhaust pipe is actually quite common. The most frequent cause is a lean air-fuel mixture, meaning there's too much air and not enough fuel entering the cylinders, causing the combustion to be slow and flames to reach the exhaust pipe. Another reason is late ignition timing, where the fuel doesn't fully burn in the cylinder and continues to burn in the exhaust pipe. In some older cars, a clogged catalytic converter can trap exhaust gases, causing the temperature in the pipe to rise. Another scenario is prolonged high-load operation, such as hauling heavy loads up steep hills, which can drive exhaust temperatures up to over 900 degrees. In such cases, it's crucial to shut off the engine immediately to cool it down—otherwise, you might even see the mounting brackets burn through. Ultimately, it's essential to check the air-fuel ratio sensor and ignition timing.
