I once recorded an average 27mpg on a tank of winter fuel using the MB factory method, commuting on fairly flat well maintained roads, after a tuneup. Mostly what I returned during the time I was actively recording mileage was 25-26.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)