Stand behind the 2007 Mercedes-Benz GL320 CDI and you won't notice anything out of the ordinary, which is exactly why you should be impressed. Look at the badge on the rear hatch. It contains the letters "CDI." Those three letters mean this is a diesel-powered SUV — the second diesel-powered Mercedes SUV to be sold in the U.S.
Walk around to the front, nearer the engine, and there's the barely detectable plunkety-ping of a diesel engine. It's not any louder than the noise made by many modern gasoline engines; it's just different.
Climb behind the wheel, the real test, and the notion that this rig is diesel powered fades faster than low fuel prices during the Bush administration. Inside, even at wide-open throttle, it's simply impossible to tell you're driving a compression ignition engine. There's no telltale black smoke and no deafening rattle. In fact, the only real giveaway comes with a brilliant torque surge that adequately motivates the GL should you need it.
It's not fast, but it gets the job done silently, cleanly and without detection. It's not the Mercedes diesel you remember.
Mercedes sees diesel engines as a perfect match for larger vehicles, rivaling the performance of gasoline engines and, now, nearly able to match their cleanliness. Even so, the 320 CDI won't meet California emissions standards, which are among the strictest in the world, and therefore is relegated to 45-state status.
But beginning in early 2007, Mercedes will offer the 3.0-liter Common rail Direct Injection (320 CDI) V6 engine in both the full-size GL and midsize ML (which goes on sale this October) SUVs. Neither will be sold in California, Maine, Massachusetts, New York or Vermont — the five states abiding by the standards.
This is not the über-clean Bluetec diesel engine that will also debut this year in the E-Class sedan and will be 50-state legal. The CDI engine uses a Variable Nozzle Turbo (VNT) to produce 224 horsepower at 3,800 rpm and 376 pound-feet of torque at 1,600 rpm. It also utilizes a particulate filter to virtually eliminate the black soot clouding your judgment about older diesel engines. The maintenance-free filter cuts particulate emissions by 99 percent. Even better, Mercedes claims the CDI engine is good for a combined fuel economy rating of almost 24 miles per gallon in the GL.
Why not diesel?
Our first opportunity to drive the GL320 CDI came on the often wet and often unpaved roads surrounding Reykjavik, Iceland. We were regularly reminded how far modern automobiles like the GL have advanced when sharing the road with cars like the Russian Lada Niva, a vehicle that, in its day, served the same purpose as our Mercedes SUV.
Even though the GL isn't going to break any acceleration records, it effortlessly powered past the Niva, riding a wave of diesel torque that's always available thanks to the GL's 7G-TRONIC seven-speed automatic transmission, which keeps the engine in its sweet spot.
After two days behind the wheel we came to appreciate the ease with which the relatively small diesel mill pushes the GL down the road. Part throttle yields nearly the same acceleration as full throttle, which encourages small throttle openings and discourages hard driving. And that's just fine in a big, comfortable SUV. The result is a fluid driving experience motivated by wads of boosted torque.
Bottom line, driving the 320 CDI is like an easygoing shuffle down an unfamiliar path. The feeling is new, but it's easy to handle and there's a smooth rhythm that makes it comfortable. The engine is blameless and gets the job done without making itself known as a diesel.
Over the tundra
Driving a premium Mercedes SUV through a climate harsh enough to prevent trees from growing seemed, at first, a little ridiculous. However, the longer we cruised down the gravel roads of the Icelandic backcountry, occasionally running across a monster-tired Toyota Land Cruiser or four-wheel-drive Ford Econoline van, the more we realized that the GL was providing equal confidence, more comfort and certainly more range (709 miles at 23 mpg) than those vehicles.
The GL's ever present smoothness was hard to ignore. Watching Thor bounce down the road in front of us in his jacked-up Toyota was laughable as the GL's air-sprung unibody danced over every rock and rut with the flow of a fat man on Ambien.
The GLs we drove were European-spec models fitted with Mercedes' Adaptive Damping System (ADS). ADS adjusts damping rates and limits body roll according to driving conditions and will be an option on U.S. models. They also had the Off-Road Pro engineering package with a modified version of Airmatic air suspension, which can increase the GL's ground clearance from 7.8 to 12 inches. The off-road package also adds more gear reduction, locking center and rear differentials, a brake-based traction control system, off-road specific ABS, downhill speed regulation and hill-start assist.
Don't bother looking anywhere but at the badge to find a visual difference between the GL320 and the gasoline-powered GL450, which starts at $54,900. The GL320 is the same seven-passenger SUV designed to compete with the Cadillac Escalade and Audi Q7. It's just considerably more efficient.
And, even though official pricing isn't yet available, it shouldn't cost that much more. Robert Moran, Mercedes' manager of product and technology public relations, points out that the diesel option in the E-Class (E320 CDI) adds a $1,000 premium over the E350 and that the difference should be about the same in the GL.
If this pricing theory proves to be true, it will be hard to make a case against the GL320. With better fuel economy, longer range and drivability that's the same or better than a gasoline engine, it's an impressive offering. At this price point the extra thousand dollars matters little. Acceleration suffers relative to its gasoline-powered counterpart, but that probably won't matter to many buyers.
What will matter is the fact that we can have the benefits of diesel power without the black smoke and awful racket we're used to from diesel engines. And that should be enough to make all buyers in the full-size luxury SUV market take notice. Even from behind.
Edmunds attended a manufacturer-sponsored event, to which selected members of the press were invited, to facilitate this report.
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