My own personal experience last summer (in my Miata, not the Civic) was on a road trip to Montana I could TELL when I hit the stations without E10 because my mileage went from 28-29 to 33-34 and I was driving more aggressively (we are talking 3rd gear runs to redline while passing on several occasions). 34 was actually my new record for the car.
BTW, the car is an 03 and runs on premium, which might even have more of an impact.
My initial goal for the Civic is 45 (old EPA highway number) and I think it's going to be tough to hit on this E10.
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