Winter time the D gets hungry due to very cold temps and snow/decreased traction. 60% of the time the Xdrive has to work decreasing the MPG dramatically in our canadian winter. I usually get around 17 combined during those months.
Retired: 2005 N52 E90 330i Sport 6AT
Retired: 2007 N54 E92 335i Sport 6AT
Current: 2012 M57 E70 X5 xDrive35D