The five-seat Mercedes-Benz ML-Class is the most popular of several sport utilities sold by the German luxury brand. Now in its second generation, the five-seat ML is being offered with a 210-horsepower, 3.0-liter turbocharged, direct-injection V6 diesel rated at 18 mpg city / 24 mpg highway by the US Environmental Protection Agency. The MSRP is $48,600, with a $900 tax credit, courtesy of the federal government’s “advanced lean-burn technology” vehicle credit.

When it was introduced for the 1998 model year, the M-Class sport-utility broke new ground for Benz. The company’s only previous SUV was the boxy, low-volume G-Class, an ancient design based on a military vehicle from the 1970s. That first ML, sold from 1998 to 2005, used traditional body-on-frame design and came close to the off-road capacity of a Jeep.

With the introduction of the second generation ML for 2006, Mercedes-Benz dialed it down a notch. The ML moved to unibody construction, and its all-wheel-drive was recast as a suburban safety feature rather than a rock-climbing off-road aid. As before, the ML is built in Alabama, now alongside two new models: the station-wagon-like R Class, and the big, blunt, seven-seat GL Class. The clean diesel versions are the Mercedes R320 Bluetec and the Mercedes GL320 Bluetec respectively.

BlueTec Makes Diesels Green

For 2009, the ML is mildly restyled and comes with three powertrain options: the new turbodiesel, a 3.5-liter gasoline V6, and a 5.5-liter gasoline V8. (There’s also a low-volume hot-rod version, the ML63 AMG.) For 2010, Mercedes-Benz will add the ML450 Hybrid—which will give the ML a unique distinction. It’ll be the sole vehicle on sale in the US that offers a choice among gasoline, gasoline-electric hybrid, and diesel versions.

In 1936, Mercedes-Benz was the first carmaker ever to offer a passenger car with a diesel engine. Since then, its legendary and durable diesels have been a point of distinction for the marque. Mercedes-Benz continues to offer diesels in several US vehicles despite this country’s stringent emissions standards, which have required it to develop entirely new technologies to make them clean enough to sell in all 50 states.

The 3.0-liter turbodiesel uses the company’s “BlueTec” suite of pollution control devices, including particulate filters and two catalytic converters. It also injects liquid urea into the exhaust stream, using the chemistry to cut Oxides of Nitrogen (NOx) emissions, which along with particulates form the Achille’s Heel of modern diesel engines.

The ML320 BlueTec is the smallest of the three Benz SUVs, although it’s still 17 feet, 8 inches long and tips the scales at 5,000 pounds. But its 18 / 24 mileage far exceeds the 15 mpg city / 20 mpg highway of the V6 gasoline version. Mileage for the 2010 ML450 Hybrid hasn’t yet been released; the industry is eagerly waiting to see how the new hybrid stacks up against the diesel.

Suburban Mom Machine

Both generations of ML can be seen in large numbers throughout affluent suburbs on both coasts. Speed and towing are not big requirements in the ‘burbs, but the ML320 BlueTec does move from 0 to 60 mph in a respectable 8.0 seconds. With a towing capacity of 5,000 pounds, it tows one-third less than the 7,200 pounds of the gasoline V6 version. Cargo capacity is 30 cubic feet, rising to 72 cubic feet when the rear seat is folded down.

Mechanically, the ML320 BlueTec comes with the superlative Benz 7-speed automatic, mated to standard all-wheel-drive. The ML includes the Pre-Safe system that anticipates accidents and pre-loads the brakes and seatbelts, among other safety features.

Like its siblings, the ML has a lengthy options list, including leather seats, an array of upgraded entertainment offerings, and niceties like a rear-view camera, voice-controlled navigation, and HD Radio with Sirius Real-Time Traffic.

Adding AdBlue

The “AdBlue” liquid urea solution is held in its own 7-gallon tank, which must be refilled every 10,000 to 12,000 miles. To comply with EPA mandates that a vehicle’s emissions system must work properly for 8 years or 100,000 miles without any owner intervention or maintenance, Benz includes AdBlue refills in mandatory dealer service intervals.

What happens if the owner runs late, or the car runs low? After a series of warnings, the BlueTec diesel simply refuses to start if its emissions system doesn’t have enough AdBlue, meaning the car must travel back to the dealer via flatbed truck. Not likely to happen, but something to consider.