Originally Posted by Lucky13
I only use 76 brand gas and 93 octane and live in the Southeast. It has 10% Ethanol or up to 10% but I think that only equates to maybe 3% less gas mileage
It's not the ethanol that's the problem[*]. The problem is that the vapor emission changes with the seasons, location and latitude. In hot weather, the gas blend has to evaporate less easily to meet the pollution standards, while during winter, and especially in the north, evaporation isn't the problem - starting bad engines is. So up North you get a lower energy and cheaper fuel that ignites easier during winter, which reduces mileage. In lowlands you also get denser less compressible air during winter, and you easily get 2 mpg less for a gas guzzler, up to 6 mpg less for a frugal car.
In the South, the gas blend is not so much of a problem, because the gas has to be blended for hot weather all year round. So your mileage shouldn't vary as much as ours.
[*]: Except for phase separation, where the ethanol sucks up water vapor from the air, and forms a sludge at the bottom of your (or the gas station's) tank. If you usually refill at half tank and only once in a blue moon on a cold day run it all the way towards empty, it can be disastrous. Sure, water injection can give bursts of extra torque, but not when done that way!
If you run on E10, draining the tank yearly can be a good idea.
Disclaimer: I work with gas metering and tank equipment.