The fuel economy gauge in the ML is pretty good. I fill the car up the same most of the time (try to fill at the same station at the same pump in the same location) and my "tank" arithmetic is within a few tenths of a point from the computer's.

The ML is very sensitive to ambient temperature. Below about 45F and it goes into a warmup cycle that chews fuel for a few miles. After the engine is considered "warm" it gets truly astounding mileage for the vehicle that it is. Also, it periodically does an exhaust system burn off cycle that I can now detect while driving - runs rich to heat the catalysts and get them to burn off any junk.

Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)