I've posted this question on this forum before, but I'm seriously dissappointed with the fuel usage on my 2010 C350 CDI sport estate, can anyone tell me why I can at the very best 36/37 mpg at between 70-80 mph when my pal gets 47 plus mpg with his E350 CDI doing the same speed, the only thing I can think of is it's a more efficient engine in the E as gearing is much the same.