varying fuel mileage

Last week the wife and I drove down to Logan, UT, 540 miles ±, on cruise control @ 75 mph in I-90 and I-15 except for the shortcut from Whitehall to Dillon, MT, at mostly 70 mph, and slowing for towns along the way until we got to the exit to US 91/191 in Idaho and on 91/191 to Logan. The calculated mileage was 44.0 mpg even. On the way home on the same roads I decided to drive at 80 mph on the interstates, and 65-70 on the two lane hiways. It was hard to tell what the wind was doing, but seemed to vary from a tailwind, to quartering from the rear on the way home, and we got 44.11 mpg calculated. I've gotten about 1 mpg better for this trip, and up to 2 mpg worse depending on the wind mostly, and driving at 75 mph on the interstates both ways.

For the people who complain that they don't always get the same mileage, I'd say that the answer is likely the wind. A 5 or 10 mph wind may not seem like much when you're standing in it, but depending on its direction it can help or hurt mileage quite a bit.

I just took my 04 BEW down to Southern Oklahoma from Bozeman, MT (3,000 miles round trip). I got anywhere from 37.1-45.9MPG, almost entirely decided by wind. On the 45.9 mpg i was doing 70, with no wind. When i got 37 it was during 300 miles of 65mph+ head- and cross-winds. Averaged 42mpgs and 80mph.