I have a 3.0 and seem to get the exact same mileage from 70 to 77mph which is 22 to 23 depending on wind. 17.5 to 18 is all the better I can get in city driving. 92000 miles on her as well.

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'03 Black BMW E53 3.0i 110,000+ miles
'03 Black Mercedes-Benz W211 125,000+ miles
'13 White Mercedes-Benz W2o4 New