Well, or so maybe you thought. Fuel labeled as E85 can contain anywhere between 51% to 83% ethanol. So, you have some mix of ethanol there, but it probably wasn’t 40%.
Yes, that’s right, 51 to 80-something% so probably less than E40 but I didn’t want to chance it with my engine. The gas mileage still dropped significantly, from 23 to 17 mpg, with whatever it was greater than E10.