Unfortunately, the reduction in weight isn’t enough to offset the loss of muscle. At 8.3 seconds to 60 mph and 16.3 seconds to the quarter-mile mark, the ML250 gives up about a second to the 7.0- and 15.4-second times delivered by the old ML350’s V-6. The torquey four-cylinder provides smart off-the-line acceleration, however, and the sequential turbochargers—a small one provides low-end boost to mitigate lag before handing off to a larger unit at higher engine speeds—do their best to keep momentum building as the seven-speed automatic imperceptibly shuffles though the gears. It’s a reasonable assumption that the suburbanites who make up the target demographic of the ML will never miss the V-6.
EPA city/highway ratings of 22/29 mpg put the ML250 right in the ballpark with competitors such as the BMW X5 xDrive35d diesel, the Jeep Grand Cherokee EcoDiesel 4x4, and the Volkswagen Touareg TDI. In our hands, the ML250 recorded 24 mpg in combined driving, an identical number to the one we measured with the ML350 V-6; we were hoping for at least a modest improvement in efficiency, given the subtraction of two cylinders and 162 pounds. What the numbers can’t communicate, however, is the 2.1-liter diesel’s willing and amicable nature. Smooth and quiet at idle (for a diesel), it has a polished quality that makes the four-cylinder compression-ignition unit in our long-term BMW 328d xDrive Sports Wagon sound a bit loutish in comparison.