i've always done that, and it's appearing that my obc is a #$*&ing liar! says im getting 25mpg. :thumbsdown:

 

That's pretty impressive! Assuming a 17 gallon (U. S. gasoline) fill up, that's ~425 miles / 17 gallons = 25 mpg (~9.4l/100km). Estimating 18 mpg in the city and 29 mpg on the highway with your city / highway mix would get you there:
29 mpg (or perhaps better) is certainly achievable from a slippery six-cylinder E60 on the highway. I recently scored 28.5 mpg (414 miles/14.513 gallons) on a highway trip in my wagon with xDrive with a light load, no a/c, and averaging 65-70 mph. We're eeking out almost 18 mpg driving around in suburbia.


Jim / crewzer

 

Well after a full tank of 91 AKI and....................


I got 360 miles.. FAIL :thumbsdown:

Not sure wtf is wrong w/my car. My OBC said I was getting 25 mpg.

 

What was your calculated mpg? If you let the car run out of fuel then that puts you around 19.5 but if it had about 2 gallons left then you are around 21-22 mpg and unless that was 100% freeway driving that is about what you should be getting.