It's often advised not to mess with what works; If it ain't broke, don't fix it. Looking at the sales boards, the Mercedes M-Class could unequivocally be called a success with roughly 1.1 million examples sold since its introduction in 1998. Still, a little updating never hurts, especially in the ultra-competitive luxury SUV segment. For that reason, Mercedes has introduced a new, third-generation M-Class for 2012 and it takes an evolutionary, rather than revolutionary, approach to staying ahead of the competition.

Helping to do just that are two new V-6 engines. The base engine is Mercedes' 3.5-liter direct-injection V-6, which produces 302 horsepower and 273 lb-ft of torque -- improvements of 13 and 6 percent over previous figures. Fuel economy is rated at 17/22 city/highway mpg, also stronger figures than the outgoing model. An extra $1500 will net buyers Mercedes' slick new turbocharged 3.0-liter BlueTEC diesel mill, producing 240 horsepower and a substantial 455 lb-ft of torque. That's money well-spent. While Mercedes claims acceleration figures are similar for the two engines (and towing capacity is identical at 7200 pounds for each), the diesel is the superior fuel-sipper, boasting an EPA rating of 20/25 mpg city/highway and a theoretical range of more than 600 miles per tank (a smaller, European-market, four-cylinder diesel option is said to be capable of roughly 900 miles per tank). At launch, all 2012 M-Class models feature 4MATIC permanent all-wheel drive, though a future front-wheel drive V-6 version will be released in late 2012.

Fortunately for the M-Class, the new engines don't have much more mass to push around. The 2012 version is stands about ¾ inches lower, it’s a half-inch wider and just 1-inch longer than its predecessor while only weighing 22 pounds more than before. The wheelbase remains the same, though track was widened by a half-inch in front and a full inch out back. Significant weight savings measures were taken to ensure that engineers could pack more standard content into the vehicle without breaking the scale. Specific weight targets were assigned by vehicle planners to keep mass low. Five pounds here, 250 grams there -- it all adds up. Aluminum was employed for the fenders and engine hood (both previously steel), and also for several suspension components. A magnesium cockpit crossmember and increased amounts of high- and ultra-high-strength steel were also specified.

Although engineers may have looked to the design of a Coke can for weight-saving measures, they didn't want the new M-Class to share its acoustic properties. Thicker windshield glass, new door seals, and sound-absorbing panels conspire to make this the quietest-riding M-Class yet. At freeway speeds, road noise is largely subdued and wind noise only becomes slightly urgent when speeds approach triple digits. Couple the isolated ride with the excellent optional 610-watt, 14-speaker Harmon Kardon stereo, and the M-Class becomes a very comfortable place to rack up the freeway miles.

Since most M-Class vehicles see duty as family transporters, Mercedes sought to make the ML a very safe place to accrue mileage. A total of nine airbags line the cabin, while attention assist and hill-start assist are standard equipment. A blind spot monitoring system and a lane departure warning system are available, with both offering passive and active notice, from a slight vibration in the steering wheel to actual braking and steering interference to bring the ML back in line should warnings be ignored. Both systems work well and can be deactivated if desired. Also on offer is Mercedes' Distronic Plus adaptive cruise control system, which will help brake the ML to a stop in panic situations as well as maintain proper distance to leading vehicles.

MB's styling department has chosen to go evolutionary rather than revolutionary. The front gets the new stout, upright family grille, the waistline has been raised, a larger roof-mounted spoiler has been fitted, and new 19-inch wheels are standard. What hasn't changed is the angled rear C-pillar that current owners identified as a defining M-Class element. Combined with the Benz's reduction in height, engineers say the new bodystyle results in improved aerodynamics and a drag coefficient of just 0.34.

The interior of the new ML 350 is rich and well-trimmed. Soft-touch materials abound, from the dashboard to the window sills, and so do premium accents. Mercedes has beefed up the standard equipment list for the third-generation car, meaning all ML 350s get eucalyptus wood and aluminum trim, heated and eight-way-adjustable front seats, one-touch up-down front windows, a power sunroof, and a power rear liftgate. Rain-sensing windshield wipers, cruise control, and an integrated garage door opener also make the list. The latest generation of Mercedes' COMAND infotainment system is present, with a 7-inch screen and optional rear-view camera and hard-drive-based navigation system with real-time traffic information. We also like the new controls layout, which feels comprehensive without being button-heavy. Responding to customer feedback, engineers switched the position of the cruise control and multifunction control stalks for easier operation, a design touch we appreciated.

We had the opportunity to drive the diesel and gasoline versions of the 2012 ML 350 on the open highways and winding mountain roads of western Montana. Our diesel tester was lightly optioned, with the standard Agility Control adaptive damping, and it proved to be both quiet and refined. Power from the diesel mill was adequate from a standstill, but the engine really shines with the turbocharger on boost at freeway speeds. Passes on narrow two-lane highways were confident, and the revised 7G-Tronic automatic transmission shifts down quickly and smoothly, skipping as many as four gears at once (steering-wheel-mounted paddle shifters are also fitted for manual control). The 3.5-liter gasoline engine was also impressive, revving smoothly to redline with a somewhat louder exhaust note than the diesel, but feeling considerably less punchy when getting on with it. Mercedes expects the take rate for its diesel engine to grow with the third-generation M-Class.

We also found the ride to be both quiet and comfortable, with good driver ergonomics and excellent visibility for a vehicle of this size. We were less impressed with the new electro-mechanical steering, which was well-weighted for an SUV, but felt a little vague. Brake feel also left a little to be desired, with more dive under heavy use than we would have liked with the standard suspension.

We came away impressed with two optional features fitted to our gasoline-powered ML 350. Advanced Park Assist works with the Parktronic system and the M-Class' new electro-mechanical power steering system to automatically parallel park the vehicle with minimal need for driver input. The driver rolls slowly past a suitable parking spot and pushes a button on the steering wheel when prompted by the display. The M-Class then adjusts the steering angle while the driver operates the accelerator and gear selection to enter the parking spot. We tried the system ourselves and witnessed others doing the same and each time it performed without fail.

We also loved the optional Airmatic adjustable air suspension, which uses air bladders in place of conventional coil springs. The system allows ride height to be raised for off-road conditions and automatically lowers the vehicle slightly at high speeds to improve both aerodynamics and stability. Airmatic also includes a dynamic damping system that adjusts rates to match present road conditions, and offers a Sport setting that hydraulically connects the two-piece front and rear anti-roll bars and stiffens damping rates to limit vehicle roll on winding roads. Left in Comfort, the anti-roll bars are disconnected and damping rates are softened for improved ride quality.

The 2012 ML 350 launches this September in gasoline and BlueTEC diesel V-6 configurations at base prices of $49,865 and $51,365, respectively -- both virtually unchanged from 2011 models. Come the first quarter of 2012, Mercedes will launch a more powerful M-Class with the new 4.7-liter V-8 found in the 2012 CLS sedan. We also were told by engineers that both hybrid and AMG versions will be available eventually.

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Truck Trend
2012 Mercedes ML 350 4MATIC
BASE PRICE $48,865
DRIVETRAIN Front-engine, AWD , 5-pass, 4-door SUV
ENGINES 3.5L/302-hp/273-lb-ft DOHC V-6; 3.0L/240-hp/455-lb-ft turbodiesel DOHC V-6
TRANSMISSION 7-speed auto
CURB WEIGHT 5100 lbs (MT est)
WHEELBASE 114.8 in
LENGTH x WIDTH x HEIGHT 189.1 x 84.3 x 70.7 in
0-60 MPH 7.3 sec (mfr est)
EPA CITY/HWY FUEL ECON 17-20/22-25 mpg
ENERGY CONSUMPTION, CITY/HWY 169-198/135-153 kW-hours/100 miles
CO2 EMISSIONS 0.88-1.02 lb/mile
ON SALE IN U.S. September 2011