25mpg isn’t great I assume?
Well, no, that would be rubbish if that was your average mpg over a prolonged period, but you said you thought you got 35-40mpg? You can’t make a decision based on say one short journey in the winter! Your car will have a different iDrive system to mine, but if you go onto the main menu, then vehicle, you should be able to find two computers – one that shows trip mpg (since you last reset – which is the same as shows at the bottom of your dash) and another which shows longer term average consumption. That’s the one you need to look at.