You are absolutely correct about the cost vs. benefits with E85, normally it's not worth it. However, after the high gas prices this summer, the engineer I am has to add "it depends". 😁
Case in point, in northwest Pennsylvania the average cost of 87 octane has been about $4.29 to $4.49 all summer long. The lone gas station around here that sells E85 has had it stuck at $2.99 since June. I average about 18-19 mpg using E85 while I get about 21-22 on regular. Doing the math for an average 270 miles I go between fill ups, E85 costs up to 7 dollars cheaper per tank despite the mileage loss! Even today with regular being $3.99 a gallon, $2.99 for E85 is still cheaper to run (the math says 4 dollars).
Another benefit with having the E85-hardware installed is you can happily run E15 (also known as Regular 88 at some stations). The same station that sells E85 here also sells E15 for about 30 cents less a gallon. In "normal" times it was usually 10 cents less. Multiple tanks of E15 in my car showed virtually no mileage loss compared to regular, so that right there is a savings too. I've run all sorts of blends of E85, E15, and regular and have never had a hiccup from the engine.
Granted, none of this will probably ever pay back the cost of the parts and labor to install E85 hardware and tuning. But if you already have an E85-capable machine, one should do the math and see. You just might be lucky and have VERY cheap E85 near you.
