Here's an interesresting thread. I found last night. Warning it's over 26 pages of threads but you can get a good idea from the first page.

Make sure your filling up at the same gas station (or same station brand holidays, bp's ect) because each gas station(brand) has a different fuel mixture.

I have a flexible fuel vehicle (2002 Ford Taurus). Back of the envelope calculations are showing me that running e85 is more expensive then straight gasoline. I get ~25 mpg on gas and ~18 mpg on e85. The only station near me that has e85 has the price locked at 30 cents less then 87 octane regular. So I suspect that it will always be more expensive for me to run e85. At least until the local station gets some competition.

Consecutive Tanks
 

The question is, how many tanks of E85 do you run consecutively? If you run straight unleaded most of the time and run a tank of E85 now and then, the ECU isn't going to compensate. You'll probably have to run at least 3 tanks to get a good baseline...

BTW, welcome to GS :thumbup:

RH77

You're probably right for the Taurus. You need to keep in mind that you are set up to run dual fuel so that it is not set optimumly for either one. I think ethonal gets a bad rap. I've had good success with E15 and on the current tank of E20 I'm sitting at 42 for the tank and that includes several city rush hour commutes and night commutes which brought it down from 44. In the end it might not be cost effective but what I like about this site is that folks test stuff out and not just go with what is considered to be fact. One thing is certain when it come to FE that nothing is certain. Time will tell. Welcome to the site.:)

I've just started tracking mpg on my ffv ranger the past month. e85 $2.99 a gallon, price never changed. reg gas was 2.80 and now 3.15. there is one station in my state that has e85 105 octane . My mileage was over 20+ with gas now its 17 or so. the molecules in e85 are spread apart more with more oxygen that burns faster than normal gas. www.e85fuel.com states 15%gas blend for summer and up to 30% for winter, the gas helps with the cold starts. so your car could run 100% ethanol but it might be hard to start.
my ffv ranger has bigger injectors to compensate for the e85 and of course the programing to automatically adjust when it senses the e85. the good thing about e85 , it got rid of my pinging and i can feel the power when I accelerate and makes 45-55% less carbon emissions.

I have also noticed a significant increase in power with E85 in my Ranger -- Driving the same route every day in a hilly, urban part of town I shift into third gear, set the cruise control at 35 MPH. The Ranger puts right up the hills with no problem. When I burn gasoline, it graduly gets slower and slower until the cruise drops out, then I have to shift to second to finish making it over the hill.

E-85 in this area was 50 - 60 cents cheaper than gasoline when gasoline hit its peak: 2.79 vs. 3.38. It is coming back down now, but is now 2.55 vs 3.09.

if it pings with regualr gas then you need a higher octane...

Nah, but maybe it makes less VOC or NMHC emissions.

I think that figure is for gasoline life cycle fossil energy consumption . The GHG is reduced anywhere from 13%-24% depending on whether it's new or old technology used to make it. More here scroll down towards the bottom.