Well written, Mike. In fact, I did immediately flush the fuel system on the KR when I discovered the damage to everything else. The KR fuel tanks had been sloshed 22 years ago with the Hirschman slosh compound. The stuff in the local Mogas had etched the surface of the slosh compound, but had not damaged the tanks. In NM, I always used one source for my alcohol free mogas. I never saw any indication of degradation of the fueling rig, or fuel systems in the planes with many years and several thousand gallons of use. After moving to AR, I only used one station after testing their fuel for alcohol and confirming there was none present. I ran roughly 250 gallons of fuel through my fueling rig and two planes over a 4 month period, then left the planes parked for a month while I was recovering from knee surgery. When I came back to them the unsloshed tanks in the Cub were leaking, as was the fueling rig. My fueling rig is a 110 Gallon steel tank, using a 12 electric fuel pump, filtration system, and flow meter with grounded fuel hose and fuel nozzle. The tank also has a DOT pressure/ventilation system. Everything on that rig is designed for use with auto gas. Surprisingly enough, the fuel damaged the internal plastic gears (that are submerged in fuel) inside the flow meter, and damaged the gasoline rated fuel hose, as well as damaging the seals in the fuel nozzle. In the Cub, I had a couple of pipe fittings started weeping after the gasoline rated pipe dope (RectorSeal) dissolved. Additionally, both composite fuel tanks started leaking, primarily where there were penetrations through the composite material for pipe flanges, such as the fuel pickup finger strainer, and the primer pump (less than 2 years old) had the O-rings fail. Fuel additives vary from station to station. Since this was not a major name brand and was the least expensive fuel in town (for alcohol free premium), I suspect I simply made the bad decision of buying from the wrong station. I now suspect this station buys cut rate plug gas fuel, then adds some sort of additive as an octane booster that is detrimental to epoxy and some plastic resins as well as many neoprene or rubberized materials. I have since had recommendations to use a different local station that is a name brand and the fuel does visually appear to be substantially different I may consider it in the future, but for now, am just a bit gun shy.
The reason for running Mogas or a Mogas/Avgas mix was not about being cheap so much as to reduce the amount of lead I was running through my engines. They simply don't need to volume of lead in 100LL fuel, and, in fact, that volume of lead is damaging to the engine. As Mike points out, when traveling cross country, the lead deposit issue can be mitigated by cruising lean. However, when dong local airport hopping, the opportunity to operate the engine lean all the time just isn't there. For now, the KR is still in flying condition. I have a rehabilitation plan for repairing the SuperCub fuel systems and should have it flying again sometime this fall. In fact, the rehabilitation plan should leave the tanks in condition to tolerate exposure to Alcohol and other as yet unknown Mogas additives without further damage. -Jeff Scott Cherokee Village, AR ---------------------------------------- Sent: Sunday, August 12, 2018 at 1:01 PM From: "Mike Stirewalt via KRnet" <krnet@list.krnet.org> To: krnet@list.krnet.org Cc: laser...@juno.com Subject: KR> Mogas Blues Based on several of the comments on this subject, some guys are missing the point of Jeff Scot's account of his gas problems. It wasn't the ethanol that damaged his fuel system components, it was something else . . . some additive(s). Jeff York makes the point that such extensive damage had to have started at some point prior to Jeff Scott's arrival in Arkansas. Since Jeff has been using his mogas/avgas mixture for many years in Los Alamos without problems, a mystery still lies at the bottom of this situation if the information Jeff York provided is accurate - that is, if the damage was cumulative, starting well before Jeff Scot left Los Alamos. I don't think so. Jeff would have noticed it. Reading the situation as it happened, Jeff Scot's fuel rig on his truck, along with the damage to tanks and tank fittings on the Cub, all happened abruptly. I would conclude it was a result of gas bought in Arkansas with some new and strange additive that is aggressively corrosive. So far it seems there's been no damage to Jeff's KR, with the same fuel. This could be that it just hasn't had time to do it's nasty work - or that the fuel tank and components in his KR are resistant to this particular mysterious additive blended into Arkansas fuel. I'd not be surprised to learn that Jeff has drained and flushed his fuel system on the KR. Jeff Scot makes the point that the lead in 100LL can cause deposits on valve stems thus causing premature wear to the guides. When I had my heads off of the GP2180, I had slight discoloration on the valve stems closest to the face. There was discoloration (a light film that came right off) also within the valve guides near the face. I threw the valves away, however I have a picture of an old valve together with a new valve and I'll attach it to this post. You'll see no accumulation of lead on the old valve. I didn't clean it up. I did clean the guides with a narrow stiff brush and they not only looked new once I'd done this, there was no play in the guide when inserting the new valve stem. In other words, I didn't have any lead build up. I had no idea 100LL had half a gram of lead in every liter. That's a hell of a lot of lead. Running lean as I do, the lead has not caused a problem with my guides despite the very high lead content of the fuel. With that much lead in the fuel, I think next time I have the engine apart I'll bump the compression ratio up from 8 to maybe 11 or 12 :-) Might as well take advantage of such great anti-detonation protection. Jeff Scot does not agree with the idea that lead acts as a lubricant as some old timers say. I tended to agree with that idea - that lead is slippery and protective. I tend now to believe what Jeff has told me about lead since he knows what he's talking about as opposed to the opinions of old timers at the hangar who base their opinions on experience and rumor and the collective wisdom of the mob and, by no means, in any case, is everyone in agreement. As it happened, my engine had suffered no accumulations of lead and the guides looked amazingly new after 500 hours, showing no wear. None. The reason for that was due to using elephant feet on the rocker arms and because I run the engine very lean at full throttle, except for takeoff and climb and, in the winter, I even lean it in the climb. Anyway, all I started this out to say was Jeff's problem has nothing to do with octane. It has to do with something strange in the mogas in Arkansas and wherever else this mysterious substance is blended into the car gas. I'll put whatever Chevron Supreme I have at the hangar in my car and even though my use of mogas has been slight, I won't be using it at all in my VW - even though the VW is originally a car engine. I have a primer, two fuel pumps, fuel valves, fuel lines, fuel filters, an Ellison carb, a fuel pressure gauge, hoses connecting all this, etc. I've never had a problem with any of these components using avgas so I'll continue to do so. I don't think they blend additives with avgas. Aviation engine manufacturers design their engines based upon the use of a fuel that doesn't bounce around with different blends compensating for the seasons. Plus, I seem to get more power out of the engine with avgas. It might be my imagination, but probably not. When I'm in the midwest buying gas for the car at those stations that sell only gas with ethanol, my mileage drops. There is less energy in gas with ethanol than in gas without it. I think it's just a matter of degree when it comes to ethanol in car gas. Premium gas probably has less ethanol than lower grades, but I suspect all gas has ethanol in it these days. I think it's something mandated by Congress to subsidize the farmers who produce it. The Chevron guy told me that on the phone if I'm remembering correctly. Mike KSEE _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. 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