What exactly "contains 10% ethanol" do?

[WhipE350]

I know when I fill my Boxster the first 1/4 tank goes really fast, it is just the gauge I'm guessing since I have had other cars that do this. It sounds like what your describing is some type of separation of the ethanol and gas with the ethanol being pulled to the engine first. I have no idea if this is possible, it's not like you are mixing water and gas. I know my old 2007 MB C230 ran that E85 and it was as expected about 30% less efficient.

Not paranoid...just do some test runs. Fill it up, drive 100 miles and fill it up again...see what your mpg is. do the same with a whole tang full, I think you'll find they are pretty close to the same...if not...ya something strange is happening.