Best was 48.5, but usually stayed around 48 going 55-60 miles per hour. Two full size passengers, one 80 pound dog, 20 pound baby, and a car full of gear.

Going my usual 79MPH by myself returns about 42MPG.

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!