I always try to buy pure gas, and I notice a significant drop in mileage when I use ethanol. That said, I sometimes wonder if I’m actually getting what I pay for, because the pure gas can cost significantly more, like $0.30 per gallon or more. I watch my mileage, have a pretty consistent driving pattern (to/from work), and sometimes notice the “pure gas” mileage drops for no apparent reason to what I get with known ethanol fill ups. If there was some sort of inexpensive kit that could instantly test for alcohol content in my fuel, I’d probably use it occasionally.
On pure highway driving (long trip, using the full tank), I get about 38 MPG on pure gas. My mileage drops closer to 36 MPG on ethanol. It’s a noticeable decline and seems to be more than energy density calculations would otherwise indicate. I wonder if anyone else has seen similar drops in performance when they use ethanol.
There are kits, or, if one is careful, it can be DIY.
http://community.cartalk.com/discussion/2146815/how-do-you-know-if-you-are-buying-ethanol-free-gas
put a small amount of pure water in a test tube and mark the amount with a line on the test tube, now fill the test tube the rest of the way with the gasoline you suspect contains ethanol put a stopper on it and shake well and allow it to sit until the gas and water separate into different layers
if the water layer is higher up the side of the test tube than it was before you added the gasoline, the gas contains ethanol...