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I have a copper colored soot clinging to the underbelly of my aircraft. It is about the color of rust water. It begins a few inches back from the exhaust and widens as it reaches all the way to the stabilator.

This Rotax 912iS has exclusively consumed 91 octane unleaded mogas (well, rarely Swift UL94 has been used but MOSTLY 91 mogas). The copper soot accumulated from the very beginning of engine usage and still accumulates at the same rate after 335 hours. Another Van's RV-12iS flyer I have met has the same copper soot on the underside. This stuff is difficult to clean off. Any thoughts on what could produce a soot of this color?

  • Re: 912iS copper colored soot from exhaust

    by » 5 weeks ago


    Auto gas (Mogas) has a brown or copper color dye in it to differentiate it from other fuels. I have a Scoda Super Petrel LS seaplane. It is a pusher configuration so the exhaust is blown over the empennage. After a long cross country, there is always a noticeable copper colored pattern that I need to clean off of the vertical and horizontal stabilizers. If I use avgas, there is no color pattern on the tail feathers.


  • Re: 912iS copper colored soot from exhaust

    by » 5 weeks ago


    Thanks! I wasn't aware of there being a copper dye in mogas,

    If I am getting build up of this copper/rust residue (that is extremely difficult to get off) is my engine running too rich? Is there a way to adjust the FADEC, if so?


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