Ethanol: It will get you coming and going

Recently, reader Frank Klein asked if he should be concerned about filling up containers of auto gas for his plane if the previous customer pumped 10% ethanol fuel from a pump island that uses a common dispensing hose for several grades of auto gas.

When I do some rough calculations, I figure that the amount of fuel contained in the hose and meter would give you close to a gallon of fuel, so if you are using a five-gallon container, you would have close to 20% ethanol-containing fuel.

I remember when I received auto gas for my farm that had been contaminated with 20% ethanol-containing fuel. It shut down every gas tractor I used it in, plus the lawn tractor and a small pickup. So yes, that amount of ethanol could cause a problem in your aircraft.

So what should a pilot do when buying fuel?

First, if it is a common-dispensing hose pump, add at least four gallons of fuel to your vehicle or other container before putting any fuel into the containers you plan to use in your plane. The second step is to always take a sample of the fuel and test it for ethanol before you ever get it near your plane.

Another reader, Ray Neal, asked what he should do when he goes south for the winter, not just about his plane, but other non-aviation equipment he stores in his hangar.

This is a major concern for pilots who use auto fuel in their aircraft. If they do not carefully check their fuel for ethanol, they can have very serious damage to their fuel system if they let it sit over the winter for several months. The problem is the fuel will expand and contract with the change in temperature from day to night. This forms moisture, which will mix with the ethanol and lead to corrosion.

So what to do? Again, I cannot stress enough the importance for pilots to always check every fuel purchase for ethanol.

Another suggestion for pilots who let their planes sit for extended periods: Run the fuel level down fairly low and then fill it with 100LL, which has much better storage stability than auto fuel — and you can be sure it does not contain any ethanol. You can also use 100LL in older tractors and yard equipment. Check your manufacturer’s recommendations.

Mr. Neal pointed out another problem: Disposing of ethanol-containing fuel. For example, if you have fuel with ethanol in your lawn mower and do not plan on using it for six months, you should drain it out and add fresh non-ethanol fuel. But what do you do with the fuel drained out? If you have a late-model gasoline-powered vehicle, you can put it in there. However, most recycle places will not take it because it causes problems in their systems.


Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at


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  1. Mark C says

    ” The problem is the fuel will expand and contract with the change in
    temperature from day to night. This forms moisture, which will mix with
    the ethanol and lead to corrosion.” I’m not convinced that the expansion and contraction will produce moisture, but it’s possible that a temperature differential between any air in the fuel tank and the sides of the tank itself might result in some water vapor condensing out. In a tank full of pure gas, this water will sink to the bottom of the tank and eventually be sumped out, however, while sitting at the bottom of a metal fuel tank, it is corrosive and will lead to rusting of the tank. Several things can happen in a tank of ethanol-blended fuel. First, the ethanol-gasoline blend is not stable, it’s more like oil & vinegar dressing, the two will separate after a while, some tests have shown phase separation in as little as two weeks. When this happens in the absence of water, the ethanol will sink to the bottom of the tank. Ethanol is even more corrosive than water, and in a metal tank, the resultant corrosion will be quicker and more damaging than would be with water. Worse, the resins used to make many fiberglass tanks can be dissolved by ethanol, resulting in both severe damage to the fuel tank and also to any fuel system and engine components which encounter this alcohol-resin mixture. (Boat guys know all about this) In the presence of water, the alcohol and water will bind and this will hasten the phase separation of the alcohol-water mix out of the fuel, where again it will sink to the bottom of the tank, and the rest of the story is pretty much the same and not good. Finally, even if the ethanol or ethanol/water mix is sumped out completely, the remaining fuel no longer has the same octane rating as it did when “properly” blended, as the alcohol component serves to raise the octane rating of the fuel.

  2. Jwboisseau says

    I accidentally put a hundred gallons of ethonal fuel in my airplane.  It cost me 4 fuel tanks, 2 fuel pumps, 1 carb over haul, LOTS of grief, BIG mechanics bill !!! Very BAD stuff!!!!

  3. F1boss says

    Hey Ben:

    If we have 20% of a 5 gallon container (1 gallon out of 5) at 10% ethanol, that does not equate to 20% ethanol in the overall ‘mix’. Seems to me it might be as low as 2%? Still, not an ideal formula IF I am correct. Your suggestion of running a few gallons into the car/truck first is a good plan. My only problem here in central Texas is there are no E0 suppliers! ARRGHH!!
    Carry on!

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