Sport Pilot Talk

Hi
Will a 10% blend of ethanol in our gas harm our Rotax 2 cycles engines, is there a down side using it in our gas??

Steve R.
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I was told in my maintenance class that it is not good to use a fuel that contains alcohol. It is bad for the engine and the entire fuel system because it attracts water.

I know guys that have ran 10% for as long as they had their engines. one 700 hrs. (two rebuilds) If you have a good set of fuel filters, they will not let water through. also drain your tank(s) daily to check for water. The water will always go to the bottom so checking before every flight will ensure you have no water going to your engine. Seems everyone you ask will have a different opinion on the ethynol issue. The biggest issue I have heard about ethynol is it eats away any rubber in the engine. I was also told that this will only happen if it is not ran frequently so who knows????????

the ethanol will absorb water so the water will not go to the bottom as long as the alcohol is only partially saturated. phase separation can then be induced by altitude or temp and pressure changes.

you wouldn't want your clean looking fuel phase separating at altitude and leading to carb ice

the ethanol can also lead to fiberglass fuel tank failures.

europe and south america uses a ethanol at much higher levels, there is a good track record using ethanol in rotax engines to date.

I have had no problems with ethanol in auto gas. Rotax now allows 10% ethanol for 2 and 4 stroke engines. It is the aircraft components that are the biggest problem such as fuel tanks, seals, lines, and filters. I just replaced a plastic fuel filter I got with a used aircraft I just purchased and it was deformed from the ethanol. I replaced it with a glass fuel filter. Most automotive components are made to be compatible with ethanol


As discussed above, the ethanol absorbs some water and it goes/burns through the system harmlessly. Ethanol basically eliminates the water problem in the fuel (unless it gets too much moisture and cannot hold any more where the water separates and could cause a problem). But generally if you get good fuel and keep water from getting into your fuel system, water will not be a problem. However, it never hurts to sump a tank. I have sumped plenty of water in AVGAS and never had water in auto fuel.

Ethanol has been shown to cause 2 stroke oil to phase seperate from gasoline. If you must run gasoline with ethanol, it is best to use an oil injection system, which completely eliminates the problem. Pre-mixed fuels with ethanol should not be stored for long periods, unless the fuel container can be agitated to remix the oil.