Mercedes-Benz has taken a risk in its quest to downsize its engine range. For 2015, the brand's popular M-Class five-passenger CUV did away with its trusty 4.4-liter, twin-turbocharged V8, and has replaced it with a 3.0-liter, twin-turbocharged V6. It's no surprise that power is down thanks to this move. Outputs of 402 horsepower and 443 pound-feet of torque are replaced by 329 hp and 354 lb-ft, but weight is down significantly as well. The new ML400 is nearly 300 pounds lighter than the 4,982-pound ML550. Will that tradeoff be enough to satisfy a buying public that's embraced falling fuel prices by buying bigger and thirstier vehicles? To find out if the blown V6 is a suitable replacement for the twin-turbo V8, we spent a week at the helm of the all-new ML400. Driving Notes This 3.0-liter, twin-turbocharged V6 is the same engine being offered in the C400 and E400 sedans. Typical of today's turbocharged engines, peak torque is spread lavishly across the rev range, from 1,600 to 4,000 rpm. That's not as generous a spread as the ML550, which offers all its torque between 1,600 and 4,750, but the power on offer is easy to access. Importantly, the new V6 never feels flat-footed or unable to answer our commands. In fact, the ML400 feels even quicker than its six-second sprint to 60 would indicate, although it's not so fast as to challenge the 5.3-second time of the ML550. After a slight and expected bout of turbo lag, the power arrives suddenly and proceeds linearly until just south of the engine's 6,500-rpm redline. The throttle response is soft in Eco mode, as expected, but sharpens up slightly when the fuel-sipping mode is off, where the gas pedal is still easy to modulate. It's a quiet engine, too. Compared to the brawnier exhaust note of the old ML550 or the howling six-cylinder in the BMW X5 xDrive35i, the ML400's note is smooth and refined, befitting of a V6. Its turbocharged nature is instantly noticed, though. Get on the throttle and the 3.0-liter happily hisses its way up the tachometer. But, it's only when you get on the throttle hard that the engine really weighs in. In day-to-day driving and traffic its soundtrack is unobtrusive and relaxed. The EPA rates the ML400's fuel economy at 18-miles-per-gallon city and a 22-mpg on the highway. That's better than the 14 city and 19 highway of the old V8 ML, but it still seems a bit low, especially for the highway figure. The ease with which we matched Uncle Sam's estimated fuel economy reinforced that theory. Like the ML550, a seven-speed automatic transmission is paired with a small set of steering-wheel-mounted paddles and sends its power to a standard 4Matic all-wheel-drive system. The trans responds quickly to throttle inputs, snapping off upshifts and downshifts with a minimal amount of delays or hunting. Unlike the engine, though, there's only one mode to work with, even if you take advantage of the paddles. It's the same sort of …
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|MPG||18 City / 24 Hwy|
|Transmission||7-spd auto w/OD|
|Power||302 @ 6500 rpm|
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