Whadayamean Unleaded Fuel Will Trash My Valves?


Now that GAMI’s G100UL is fully approved and awaiting distribution, owners are hearing questions about how unleaded fuel might cause valve damage in aircraft engines. It was once a thing in car engines, but in this video, AVweb’s Paul Bertorelli examines the issues and finds valve seat recession an unlikely consequence of using unleaded aviation fuel.

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    • Squared, Raf. To do the story line initial layout, topic research, drawings and photo layout, come up with the spoken words and then assemble it into a coherent package is a talent PB has mastered. He makes it look easy. Every time he ‘disappears’ for a while, I always think … hope he’s coming up with something good. In THIS case, he did. Good job, Paul … and thanks.

      Hopefully, EAGLE will take longer than 2030 and the plant in UK doesn’t burn down.

  1. Right. Unleaded fuel won’t cause valve seat recession. I have indeed seen it happen with automotive engines. Ones that were born and bred to run on Unleaded fuel. Don’t worry. We’re the experts. We know what we are doing…..

  2. I think it would be worth a call to EAA and Peterson about their auto STC data. If aircraft using auto fuel are having any issues you would think those two outfits would know. I know of a large number of aircraft that run exclusively auto fuel from their first hour on and have no complaints.

  3. I flew skydivers at several Cessna 182 drop zones in the 1990’s and their mechanics, one of which overhauled its own engines, never mentioned anything about valve seat issues when using auto fuel in the O-470 engines. I knew another owner of a beech 18 who also used unleaded autofuel in his jump plane and never complained about valve seat issues.

  4. The issue that is about to hit many engines is NOTHING whatsoever to do with the valve seats and valve faces …… just btw. It’s amazing how many gaps there clearly are in the ‘so called experts’ knowledge.

  5. Paul, having zero compression on any cylinders is not cause for an engine rebuild. I know you said that tongue-in-cheek, but many people seriously believe this. We have 5 to 7 engines working on concert as one engine. Not having hardened valve-seats until 2019 (at least from Continental along with their pre-modernization valve-guide boring machines) is further evidence that one might be fine just topping the engine. The fuel affects the cylinder assembly primarily. It just seems to be that a lot of money in aviation gets spend on premature overhauls that could be used elsewhere.

    Another thing that may or may not be related, though you do mention it in your video, is valve-rotators. If these fail, and they frequently do, a burnt valve is practically guaranteed. I’m of the camp that favors replacing the rotators on-condition (engine-monitor required), or even every 500 hours. May or may not be lead related as lead by-products do end up in the oil, which is another factor in favor of using unleaded, which is cleaner oil.

  6. As things change you need to change with them. To run unleaded, say, in a 1940’s Lyc. engine designed for leaded fuel will someday (not immediately) prove detrimental to your health. Proper mods are expensive, but so are funerals.