2008 ML320

Mercedes-Benz doesn't usually wind up on top in fuel economy — unless the Mercedes you're looking at has a turbodiesel engine.

Mercedes officials have been adding their fuel-thrifty, new-generation, 3-liter turbodiesel to more models and boosting fuel economy significantly in the process. The result: The 2008 diesel ML320 CDI sport utility vehicle has the best federal government fuel economy rating of any nonhybrid, luxury-branded midsize SUV of the 2008 model year.

The rating is 18 miles per gallon in city driving and 24 mpg on the highway, which is commendable for a midsize SUV weighing more than 4,800 pounds. Total city/highway mileage on a tank of diesel in the Mercedes ML320 CDI can be as high as 500-plus miles.

In contrast, the ML with a gasoline V-6 and a weight that's 100 pounds less than the diesel model gets a mileage rating of only 15/20 mpg.

Best of all, compared with complex gasoline-electric hybrid vehicles that usually carry a price premium of $3,000 or more over gasoline vehicles, the starting manufacturer's suggested retail price, including destination charge, for a 2008 ML with diesel is just $1,000 more than the starting retail price for an ML with gasoline engine — $45,825 vs. $44,825. All MLs come standard with 4Matic four-wheel drive.

Yet not everyone who might want a diesel ML can get one. The diesel engine does not yet comply with vehicle emission regulations in California, Connecticut, Maine, Massachusetts, New York, Pennsylvania, Rhode Island and Vermont.

The ML320 CDI can't be registered in these states. Mercedes engineers are working on this issue, because the automaker wants to sell diesel models in all 50 states in 2009.

Meantime, shoppers looking for a family-friendly, five-passenger, luxury-branded image vehicle have some options. They can select from the 215-horsepower diesel engine with a stout 398 foot-pounds of torque starting as low as 1,400 rpm and three gasoline powerplants — the 268-horsepower V-6 with 258 foot-pounds of torque starting at 2,400 rpm and two V-8s, including a 503-horsepower, 6.3-liter unit capable of 465 foot-pounds of torque at 5,200 rpm.

The ML also has a slew of optional features, including a Harman/kardon sound system and headlamps that swivel to illuminate the way around curves in the road.

But Mercedes continues to suffer problems in quality. Predicted reliability of the ML is "poor," according to Consumer Reports.

The test ML320 CDI sipped fuel efficiently, even while feeling heavy, solid and stable. Without changing my driving style and without trying to get optimal fuel economy, I averaged nearly 21 mpg in city/highway travel. And with a 25.1-gallon tank that's larger than those on many other SUVs, the ML didn't require frequent stops at the gas station.

The engine's quick response was noticeable, and I enjoyed the power that came on fast and strong, especially at low rpms. The torque — that "oomph" that propels the vehicle — is palpable, thanks to the turbodiesel, and the seven-speed transmission shifted smoothly.

I just hated the little stalk that the electronic shifter was on, off to the side of the steering wheel. It takes practice to learn just how to move the stalk correctly to get it into the correct gears.

The ML rode stably and there was no tippiness, even in mountain twisties. A button inside the vehicle allowed the driver to change the settings of the shock absorbers, and the changes really did affect how stiffly or how compliantly the vehicle rode.

The tester wore 19-inch, all-season tires, but the ML interior remained quiet, with nary any road or engine noise. The few times I heard the engine, it was subtly clear, from the minor diesel racket, that the hood covered a diesel.

The ML seats in the test vehicle were firm and supportive and had optional leather trim. They were positioned a good bit above the pavement, but they weren't so high that passengers had to climb up to get inside.

Views out the front of the ML were good, as everyone could look beyond the cars and even some smaller trucks. But it can be difficult for the driver to see what's directly in back of the ML when backing up, so the optional rearview camera and/or parking sensors are advised. Both were options on the test vehicle.

Rear-seat legroom and headroom are noteworthy, and with back seats folded, the rear cargo area offers a competitive 72.4 cubic feet of space.

I have to admit that I'm tired of the same old look to Mercedes' central stack on the dashboard. The display screen is smaller than on many other, lower-priced vehicles, and the swarm of buttons around the screen in the tester was daunting.

The navigation system also has a clunky, old-style array of buttons compared with what's available in some other, newer systems in other vehicles.

All ML models received across-the-board, five-out-of-five stars in U.S. government frontal and side crash tests. Standard safety equipment includes front knee bolsters, curtain air bags, side air bags and electronic stability control.

Early this calendar year, Mercedes recalled 9,004 diesel-powered vehicles from the 2007 model year because of crankshaft sensors that could fail. Failure would cause the vehicles to lose power and the ability to restart, according to the National Highway Traffic Safety Administration.

The recall covered diesel-powered versions of the 2007 ML320.