Found this on the net. Ethanol and Rotax engines What's its effect?. Phillip Lockwood Question: What problems if any are associated with the use of E10 fuel in Rotax aircraft engines? Answer: Fresh autogas without alcohol a is the preferred fuel for all Rotax aircraft engines. However, in many parts of the United States and Canada, gasoline is blended with 10-percent ethanol to produce a product referred to as E10 fuel. Ethanol is an alcohol commonly made from corn or sugar cane. The added ethanol in E10 fuel offers advantages and disadvantages. The Advantages: Ethanol acts as an oxygenate, which means it adds oxygen to the gasoline. Ethanol is 35 percent oxygen by weight and replaces methyl tertiary butyl ether (MTBE) to help the fuel burn more completely and cleanly, thus reducing smog-forming and ozone-eating emissions. Adding 10 percent ethanol increases a fuel's octane rating by two or three points. Widespread use of E10 fuels will significantly reduce our dependence on foreign oil. Because alcohol absorbs water, gasoline with added alcohol should help keep fuel systems free of water, so water should not be present when sumping the tanks and/or gascolator on an aircraft filled with E10 or any Officially, Rotax has approved the use of fuel with up to 5 percent alcohol content. Other than a slight increase in the exhaust gas temperatures (EGT), the engines seem to work fine operating on blends with up to 10 percent ethanol. Most autogas produced today has at least some alcohol mixed in to help reduce unwanted auto emissions. The Disadvantages: When using E10 or any fuel with alcohol in any aircraft application, potential problems exist. The greater the percentage of ethanol, the greater the chance you will experience problems, which can include the following: Damage to rubber gaskets and composite fuel tanks. E10 fuel is not as friendly as avgas or pure gasoline to these components. The aircraft fuel system must be compatible with E10 fuels to avoid this damage. Corrosion problems with metal tanks, electric fuel pumps, and other fuel system components. Ethanol, or any type of alcohol, readily absorbs water. It may even absorb signiffcant amounts of water from the atmosphere in humid conditions. If too much water is absorbed, phase separation can occur, which results in the water and ethanol combining and falling to the bottom of the fuel tank. This combined water and ethanol can be quite corrosive to metal tanks and fuel system components, especially if the water and alcohol are allowed to remain in the bottom of the fuel tank for some length of time. If properly equipped with fuel tank sump drains, the water/ethanol combination can be drained off leaving only the gasoline, but it will have a slightly reduced octane level--down by 2 to 3 points using the antiknock index (AKI) rating method. (The Rotax 912ULS, the turbocharged 914, and the two-stroke 618 engine all require 91 octane fuel using the AKI rating method. The 912UL (81-hp) and the two-stroke 447,503, and 582 engines will run on 87 octane.) Because of ethanol's propensity to absorb water: Frank.