Besides just wanting to try E85, I thought of it as a different kind of solvent than gasoline and perhaps there was something that could get cleaned up after 17k miles. That was the idea, but it wasn't backed by facts.

My fuel consumption in miles per dollar was a surprise. My last E10 tank's data was:
miles = 464.2, gallons = 29.8, $/gal = $3.59, cost = $106.98, mpg = 15.6, miles/$ = 4.34

That tank had an unusual 140 miles of Interstate and my usual mileage is from 13.8 to 14.1 mpg.
Presuming 14 mpg the data would look like:
miles = 417.2, gallons = 29.8, $/gal = $3.59, cost = $106.98, mpg = 14.0, miles/$ = 3.90

My E85 tank's data was:
miles = 379.1, gallons = 31.75, $/gal = $2.89, cost = $91.76, mpg = 11.9, miles/$ = 4.13

At these prices E85 is cheaper per mile. I don't know if the E10 to E85 cost ratio that I encountered is typical. Just in case I wasn't clear, I tried to have equivalent data and my "synthetic" 14 mpg data is intended to normalize the E10 to E85 comparison.

('11, 6.2L gas, extended cab, short bed, white, parked facing south)

 

I'd run a few more tanks of E85 through to get a baseline. With only one tank you'll still have some E10 in there to dilute the E85 and that will skew the numbers a bit. I've been waiting until I get a few more miles on my truck before I try E85, but on my wifes old truck she would loose a couple miles to the gallon with E85. I can't remember the exact numbers, but E85 needed to be $.50/gal cheaper than E10 just to break even. In our area it's rare that E85 will be that much cheaper so we didn't run it much.

 

I figured that this was 86% E85 so that was close enough. Also there was a $.70 difference in this example.

I don't believe it matters, but I live at >6,000 feet above sea level so our regular E10 is 85 octane. I am under the impression that it is the same as sea level 87 octane but measures differently since we don't have oxygen here.

 

I do not have the exact numbers , but , my 04 flex fuel Mounty gets much worse mpg on E85 . Only used it a few times while on the road . I now avoid it .

 

e 85 in western pa is only .16 cents cheaper than 87oct. wont even try it for that price. especially if it needs to be at least .50 cent cheaper to be close

 

You will get worse mileage, but the key is your cost per mile.

 

this is correct, you need to figure cost per mile to see if the cheaper price of E85 is enough to offset the increased fuel amount you will use due to the mileage loss E85 causes. Every vehicle is different so you need to run a few tanks of each through and see what you get.

 

Sure , given enough use I could calculate . However it is not sold in my local area . But I avoid it while traveling after showing such a bad drop in mileage .