Just did a brim tio brim test and after converting km to miles etc my average over the last tankfull (794km) was 27.9 miles per imperial gallon. OBC showed 24.5 miles per US gallon (= 29.4 miles per imperial gallon) so the OBC is about 5% optimistic, pretty much what I've had on previous BMWs.
Peter T

That is on the diesel, presumably? Winter fuel?

My OBCs have all been much closer than that. Would be interested in whether you have the same delta on summer fuel.

Yes - it's the 35d - I should have said. Will check in a couple of months when we are on summer diesel but as I say my previous experience on several BMWs is that OBC is about 5% optimistic.
Peter T

My long term average is 17.5. The wife drives it, so the speeds are slow with light acceleration mostly.

I just hit 2000 miles on my 35i and according to my computer, my average speed is a tad over 31 mph and my average mileage is 20.1 mpg. I haven't reset it since I got it back in January. Seems pretty good to me for such a low average speed.

I would say that it is, yes.

That implies lots of city driving - as is my case - and at 10K miles mine still shows 19.6MPG.

Are you in the habit of performing "aggressive" starts?

It seems that in this vehicle, it does not make as big a dent in fuel economy as perhaps others. One comment (from a car full of Porsche drivers) was "you get 19.6? Driving like THIS!?"

20.1 seems quite good to me; probably just a bit above where I would expect.

It's a good feeling really, isn't it?

When you take your first long highway trip and get about 26MPG, you'll feel even better.

All relative, I suppose.. But when I hit it on a long highway trip I just said "WOW."

Agreed. The OBC on my wife's 35d is always close... for example, at the last fill up I hand calculated 23.5 mpg to the OBC's 23.7.

My 35d seems to have "loosened up" around 4000 miles, getting 23+ MPG on the last two tanks while struggling to get more than 22 MPG on the first few tanks. The weather has been no warmer nor has my driving style or conditions changed, so it seems likely that the engine is getting broken-in. I've read that the diesels do even better in warmer weather, so I'll look for 24 to 25 MPG in the coming months. Not bad for a 2.5 ton vehicle.

My d has been pretty thrifty so far. This is 85/15 congested city/highway mileage.

http://i118.photobucket.com/albums/o..._5086979_s.jpg

12.5 MPG on my 5.0 Ouch!!! My 4.8 got around 15 MPG so it is a huge differance.