Is R-Class a wagon, minivan or SUV?

This undated picture made available by Mercedes-Benz shows the 2011 Mercedes-Benz R350 BlueTEC. (AP)

Some six years after its U.S. debut, the Mercedes-Benz R-Class people hauler continues to struggle.

Sales for the $50,000-plus six- to seven-passenger vehicle last calendar year remained below 3,000. Influential Consumer Reports predicts R-Class reliability that's much worse than average. And there's also debate about what the R-Class is, exactly.

With a newly styled front end for 2011, it has more of a sport utility look than before. But from the side, it still looks like a minivan and station wagon.

One highlight, though, compared with competitors from Lexus, Lincoln and others: The R-Class is available with a fuel-savvy and strong diesel engine.

This six-cylinder powerplant delivers a whopping 400 foot-pounds of torque at a low 1,600 rpm for quick off-the-line response even as it boosts the federal government fuel economy rating for the R-Class by 25 percent compared with the gasoline R350, combining city and highway estimates.

Starting manufacturer's suggested retail price, including destination charge, is $51,115 for a 2011 R350 with gasoline engine. The 3.5-liter turbocharged diesel V-6 adds $1,500 more, for a starting retail price of $52,615 for a 2011 R350 Bluetec.

The Bluetec moniker from Mercedes indicates the engine is a modern diesel with lowered emissions, not an old-style diesel that had difficulty meeting U.S. emissions standards in states like California.

A leader in the segment — the long-running and popular 2011 Lexus RX — is available with a gasoline V-6 and a hybrid gasoline-electric powerplant, but no diesel. The RX, whose sales last year totaled more than 95,000, also does not offer third-row seating. But the RX has a much lower starting retail price than the R-Class — $39,350 as a base model and $44,810 as a hybrid.

Meanwhile, the 2011 Lincoln MKT, which has three rows and gasoline V-6s, starts at $45,035, and the 2011 BMW X6 starts at $57,875 with gasoline six cylinder and $89,775 as a gas-electric hybrid with V-8.

The Lincoln and the X6 outsold the R-Class last year, too.

To be sure, the R-Class styling is distinct, with the roofline narrowing to a sharp V-shape as it dives down to the vehicle's body at the third row seat. This is supposed to evoke a stylish coupe, but it doesn't work for me.

Despite the "350" in the name, the diesel version of R-Class doesn't have a 3.5-liter engine, the way the gasoline R350 does. The diesel is a 3-liter, double overhead cam V-6 that's turbocharged and delivers 210 horsepower compared with the 268 from the gasoline V-6.

Still, the diesel's 400 foot-pounds of torque is outstanding and made driving the heavy R-Class tester enjoyable. Peak torque from the gas engine is 258 pounds starting at 2,400 rpm.

The U.S. government's fuel economy rating is 18 miles per gallon in city driving and 24 mpg on the highway for the diesel R350, compared with just 15/19 mpg for the gasoline-powered R-Class.

Unlike an SUV, the R-Class doesn't require passengers to make a big climb to get inside. And rear doors are especially long, providing wide doorways for second- and third-row passengers to enter and exit. Drivers just need to remember how long these doors are when they park. Otherwise, rear-seat passengers can bang the doors into adjacent cars in parking lots.

The test R350 Bluetec was nearly 17 feet long, which is even longer than a Cadillac Escalade. So I was conscious of making wide turns to keep the rear wheels from hitting curbs. But steering effort was light.

At more than 5,000 pounds, the R350 rode like a solid, heavy vehicle. The Teutonic character came through as the test vehicle's weight shifted from one side to other in twists and turns. The car wasn't unsettled in these mountain road maneuvers, but passengers sensed they had a lot of mass around them.

The suspension managed the ride and handling well, keeping most road bumps away from passengers. Thanks to a quiet, well-insulated interior, I scarcely heard the diesel engine or road noise, even though the tester had big, 19-inch tires.

The length of the vehicle contributed to good legroom in all three rows. Headroom in all three rows is good, too, though not quite as much as in the higher-riding, three-row Escalade.

Adding to the roomy feel in the test R350 was a panorama moonroof. Option cost: $1,090.

Fit and finish on the tester was excellent, and overall, the interior was well-crafted. Seats were firm and supportive.

Radio and navigation controls, though, weren't intuitive. The display screen in the dashboard also wasn't as large and colorful as some other cars have.

While the R350 comes standard with many safety features, including curtain air bags, anti-whiplash front head restraints, electronic stability control and Mercedes' programmed pre- and post-collision safety systems, it seemed odd that a rearview camera was optional.

A blind spot warning system is offered now for 2011, but it, too, is an option at $600.

The tester came standard with all-wheel drive that didn't require the driver to do anything to engage. It helped provide sure-footed travel in heavy rainstorms.