One of the main problems with ethanol based eco-fuels is their propensity to absorb water. The mixture is entirely missible, as opposed to the usual scenario with oil/water or petrol/water mixes, where the petrol or oil floats on top of the water.
Therefore there won't be a visual clue as to the loss of grade of fuel or to the potential for corrosion. Obviously, with aircraft that are being used intensively, there will be little opportunity for problems to arise, but in the instance of aircraft that are stored, or used irregularly (as with much of the GA fleet), there might be difficulties.
I don't want to look for problems, as anything sensible that might be used as a solution to an inevitable shortage of petroleum based products should be welcomed, but as things stand there ethanol based fuel will create maintenance issues.
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