Quote Originally Posted by 89Vette View Post
Well this is the first winter with E10 (where we didn't have a lot of snow). With all the warm weather, people should be seeing higher avg MPG than E10 might dictate. (FWIW, if you didn't know: Alcohol returns less energy (BTUs) for a given combustion cycle. So, there's no way we'll get the same MPG as the 100% gasoline days.)
It's not as big a difference as you might think.

Ethanol contains roughly 80% of the btus of gasoline. So if the mix is 10% ethanol, you still have 98% of the btu as before. So you can expect 2% less btu and hence, mpg. So if you were getting 16 mpg before with straight gasoline, it will "plummet" to 15.68 mpg with 10% ethanol.