A friend of mine bought a new Chevy 1500 with Flexi Fuel capabiliy. After driving a month using Flexi Fuel he's not very happy with the package. The mileage drops from 17/18 for reg unleaded to 9 when using Flexi Fuel and the truck has a hard time towing his Toyota rock crawler and 18ft trailer while burning Flexi Fuel.
Flexi Fuel cost's .40 a gallon less than reg unleaded with mileage drops like this you'll never recoup back the cost of the option.
I've just started to do some pretty in-depth study into this concept. Essentially, flex fuel allows a vehicle to be either gasoline or e85.
From what I've read and heard, the fuel injection systems that allow a vehicle to go from gas (90% gasoline - 10% ethanol) to E85 (15% gasoline - 85% ethanol) aren't perfected really well yet. Apparently, future fuel/air mixers will provide even more energy to be earned from E85, providing better performance and/or better economy.
From what I've been told, right now just about eveyrone says that they get about 30% worse mileage on E85 instead of gasoline. That's pretty dramatic, but the fuel costs less too, so it almost averages out.
The plus side is that it's made from renewable engery sources, so it's cleaner burning and it's a fuel that can be grown in the US, or at least in North America to eventually provide enough fuel for the entire nation. They're even talking about being able to get down to the cellular structure of switchgrass in the near future to get the alcohol from that. That would be interesting.
