I wonder how much impact running the air conditioner has because I have always gotten better mileage in winter months when I rarely use the air except to remove humidity like on rainy days. I typically get 1-2 mpg better in winter, keep in mind that in summer when its 96-100 every day and humid here in SC my air conditioning is getting a major workout.
1995 325i,1996 328ci,1997 528i,1997 Z3 2.8,
2001 X5 3.0,2001 330i Conv,2002 M3 Conv,
2003 M3 Coupe,2004 M3 Coupe,2004 Z4 3.0,
2004 X3 3.0,2007 X3 3.0,2007 335i Conv.,
2013 X1 28 sdrive M Sport