2009 Mercedes-Benz M-Class Road Test Review

So what's the big deal about the 2009 Mercedes-Benz ML320 Bluetec? Simple: Its clean-burning 3.0-liter V6 (shared with the GL320 and R320) is the first diesel-fueled engine (other than Dodge's heavy-duty truck diesels) to pass the stringent 2010 EPA emissions requirements for 50-state certification. While diesels are a fixture in European-market vehicles, the U.S. government has long been leery of the high particulate emissions endemic to these engines. Thanks to Bluetec, stateside Mercedes buyers can enjoy all the benefits of diesel, including superior fuel economy and a reputation for durability, with the full blessing of Uncle Sam.

Sounds like a win-win proposition, right? And it would be, if this Benz boasted the expected instantaneous turbodiesel torque off the line. However, there's an exasperating delay when you floor the throttle from a stop or forward creep, as though the transmission has been caught off-guard. Forget Mercedes' claim on its Web site of "V8 power in a V6 configuration." Thanks in part to this conservative shift logic, the ML320 Bluetec would have its hands full keeping up with an ML350 and its gasoline-powered V6.

Fortunately, the Bluetec does deliver considerably more miles per gallon when it's time to refuel, though diesel continues to outpace gasoline in the price column as of this writing. Whether you'll enjoy yourself between fill-ups is another matter. Granted, the sumptuous interior appointments are beyond reproach — our test car's upper-crust cabin made the $61,200 asking price seem downright reasonable. But given its gooey steering and ho-hum performance, the 2009 Mercedes-Benz ML320 is probably best experienced from somewhere other than the driver seat.

Nonetheless, this Benz's combination of top-shelf luxury, superior fuel-efficiency and environmental friendliness is bound to win over a good number of deep-pocketed SUV shoppers. In this era of volatile fuel prices and an uncertain automotive future, clean diesels hold considerable appeal as a green alternative to the status quo.

Performance

The four-wheel-drive 2009 Mercedes-Benz ML320 Bluetec is motivated by a 3.0-liter turbodiesel V6 that has been engineered specifically to achieve 50-state emissions certification. The U.S. imposes more stringent tailpipe particulate emissions standards than diesel-crazy Europe, so Mercedes added a tank of AdBlue urea and water mixture (hence "Bluetec") to the exhaust system. When the engine is running, AdBlue is automatically injected into the exhaust stream, catalyzing a chain reaction that results in the conversion of polluting nitrogen oxides into harmless water vapor and nitrogen. Voilà! A diesel that even the Green Party could get down with.

The Bluetec diesel V6 cranks out 210 horsepower and 398 pound-feet of torque. A seven-speed automatic with manual-shift capability — the only available transmission — routes the power to all four wheels, with selectable low-range gearing. At our test track, the ML320 ambled from zero to 60 mph in an adequate 8.5 seconds. Braking was superlative for such a heavy vehicle — at just 121 feet from 60 to zero mph, the 5,129-pound ML320 stops better than most midsize sedans. Maximum tow rating is an impressive 7,200 pounds.

Not surprisingly, the ML320 is hardly a driver's SUV in the real world. The diameter of the steering wheel is buslike, and that about sums up the steering feel, too. There's an unpleasant amount of play in the ML's tiller, and it feels like it's communicating with the tires via telegraph. Handling limits are perhaps a smidge above average for this segment, but there's too much jello in the suspension to encourage enthusiastic driving. Our test car's optional Airmatic electronically adjustable suspension seemed pointless, as cycling from Comfort to Sport merely dialed up the impact harshness while failing to rein in excess body roll.

We expected things would take a turn for the better when we put the Benz's pedal to the metal. No such luck. The Bluetec diesel does provide a satisfyingly torquey kick, but not until the ponderous transmission says so. When you floor it, there's an exasperating delay (one-one thousand...) while the seven-speed slushbox unhurriedly mulls over your command, rather than the prompt rush of torque that we'd expect. The only way around this is to brake-torque the ML320 from rest, which isn't a technique owners are likely to employ.

Where the Bluetec shines is at the filling station. The ML320's EPA ratings of 18 mpg city and 24 highway trounce the gasoline-powered ML350's ratings of 15 mpg city/20 highway. We observed an admirable 21.1 mpg over more than a thousand miles; remarkably, this matches the lifetime average of our long-term Honda Accord EX-L V6 midsize sedan. When SUV versatility meets family sedan fuel economy, you know there's something special happening under the hood.

Comfort

Despite the ML320 Bluetec's undisciplined body motions in corners, it rides rather firmly, even with the suspension in Comfort mode. As is typical of German vehicles, though, impacts are rarely intrusive (unless you're tooling around in Sport). While there's plenty of diesel clatter outside the ML320, noise levels inside are luxury-car low at all speeds. The optional power-adjustable leather-trimmed front seats were supremely supportive, with firm bolstering that helped keep us alert on longer journeys. The backseat is nearly as inviting, boasting a chairlike seating position and ample headroom. Only passengers of above-average height will find rear legroom a bit lacking.

Function

Visibility in the 2009 Mercedes-Benz ML320 is superb, thanks to an elevated driving position and plenty of glass all around. The center stack controls are a nightmare, however, as the ML320's COMAND interface lacks the control knob we've come to expect in premium vehicles, forcing you to use four directional arrow keys and an "OK" button instead. Predictably, most audio and navigation commands require numerous clicks — up, down, right, "OK," down, and so on. Compounding the problem is the smorgasbord of identical-looking black buttons, which fail miserably at making your life easier.

Some thoughtful touches elsewhere helped to mitigate our frustration somewhat. For example, there's a nifty two-mode switch mounted on the inside lip of the tailgate — the first function closes the tailgate automatically, while the second closes it and then locks the entire vehicle. Also, the glovebox-mounted iPod interface works seamlessly, allowing song selection by artist name, track name, playlist name and so on. Disappointingly, the uplevel Harman Kardon stereo lacks clarity and provides generally mediocre sound.

In our real-world usability tests, a rear-facing child safety seat fit fine in the ML320's accommodating rear compartment, though taller front passengers may have to slide their seats forward a little. Golf clubs are a different story. We expect a midsize SUV to have plenty of club storage space, but the ML doesn't provide enough horizontal room for even a compact carry bag. Depending on the length of your driver, you might have trouble fitting your bag lengthwise as well, leaving you with two options — go diagonal, or fold down one of the rear seatbacks.

Design/Fit and Finish

The 2009 Mercedes-Benz ML320 boasts a beautifully constructed interior, with high-quality materials virtually everywhere you look and touch. Indeed, the Benz's interior design and quality may be its most outstanding feature. Compared with the rival Lexus RX 400h, the ML320 feels (and is) thousands of dollars more expensive. Fit and finish was excellent with the exception of a slightly misaligned steering wheel cover.

Who Should Consider This Vehicle

Shoppers who want a luxurious SUV with solid green credentials. Be advised, though, that the Lexus RX 400h offers superior performance and fuel economy in a more affordable package, the Mercedes-Benz GL320 Bluetec or R320 Bluetec will give you near-identical fuel economy and considerably more interior space, and the Jeep Grand Cherokee CRD is both swifter and far cheaper.

Others To Consider
Jeep Grand Cherokee CRD, Lexus RX 400h, Mercedes-Benz GL320 Bluetec.

The manufacturer provided Edmunds this vehicle for the purposes of evaluation.