Ernst, I'm not trying to be close-minded, and I'm glad you and others have enjoyed success in using E10 fuel in your aircraft. What I am trying to do is reasonable risk-mitigation, even at the recognized expense of paying a premium for no-ethanol premium mogas for my 8.5:1 IO-540. There have been batches of this fuel that I paid very nearly as much for delivered to my house by the farmers' co-op as I would have paid at the pump for 100LL at the cheapest airports around these parts, largely negating my chief reason for running mogas.
Here is my chief reservation, aside from the uncertain pedigree of certain seals and elastomers in my fuel system and the sealant in my tanks. This is from the internet, of course...
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As noted on Chevron's Web site, while conventional gasoline can dissolve up to 150 parts per million of water at 70°F, the situation is different for gasoline oxygenated with 10% ethanol. This 90% gasoline/10% ethanol blend can dissolve up to 7,000 ppm of water at 70°F. When this blend is cooled (insert adiabatic lapse rate here) , both the water and some of the ethanol become insoluble. Contacting the blend with more water also draws ethanol from the blend. The result, in both cases, is two layers of liquid, an upper ethanol-deficit gasoline layer and a lower ethanol-rich water layer. This phase separation of the gasoline/ethanol mix lowers the octane number and may cause knocking in an engine, while the engine will not run at all (I don't like the sound of that) on the ethanol/water layer (which of course collects down there at the bottom of the wing tank where the fuel pickup tube sits).
Because of this potential for phase separation at any ethanol level, it is imperative that motor fuels containing ethanol not be exposed to water during its distribution (and just how are we to assure ourselves of that?)or use, making housekeeping at the service station and any other points along the supply chain very important in the prevention of water contamination. Another property of ethanol blends is that they are hygroscopic, meaning they absorb moisture from the air, raising the potential for phase separation during storage if the tank is vented to the atmosphere (which is how we build our RV tanks, of course)and is subject to condensation formation as a result of temperature change.
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Like I said, not trying to lecture or be snarky - just reasonably risk-aware. My take thus far is that use of E10 in aircraft fuel systems is not a problem right up until the moment when it is. I am choosing, for now, not to buy a ticket on that ride. Budgetary considerations and the relative price of E10 and 100LL may force a rethinking of the issue, but it will be with the uncomfortable awareness that bargain-hunting is shifting my window of acceptable risk. Perhaps when I cannot afford the pure stuff, it's time to get out of the game altogether and let a more affluent person own my plane. Who knows.