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Exhaust Pipe Discoloration

seattleworm

Well Known Member
Sponsor
Do you think this is normal? The two exhaust pipes got very different discoloration in my RV 7 (Lycoming IO-360-M1B). One "looked" much hotter than the other. This unevenness is only at the outlet end of the pipes. Inside the cowl, the colors of the two pipes look similar. the "hotter" (darker) pipe actually looks more burned at the outlet end than inside the cowl. This puzzled me. the outlet end should be much cooler than inside the cowl due to cold air stream. The engine is running normal and smooth. EGT spread is about 60F max between cylinders. The soot inside the two pipes looks the same in terms of color and quantity. Don't know when and how this is developed, the engine got about 106 hrs since new. Is this this something I should be concerned with as long as engine parameters are within spec? What could have caused this. Looking for some ideas.

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If there is nothing mechanical, such as oil leaking onto the pipe I would talk to the exhaust manufacturer. My opinion is that it could be a different grade of metal in the pipe. I am basing this on having worked with different grades of Stainles steel which look as your pipes do.
 
Normal according to Vetterman Exhaust

I sent the same pictures to Vetterman Exhaust, Clint of Vetterman said different colors on pipes are normal due the air stream at exit is different, nothing to worry about as long as engine is running normally. I believe in my case it might be combination of different air stream and oil coating. I remember during one of the oil changes I spill lot of oil on the pipe. I just wiped it off using paper towel. Maybe the thin oil film got burned and made the darker appearance on one of the pipe.
 
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