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Diesel passenger cars in the U.S. have long suffered from a market that takes two steps forward and one step back, then spends years taking no steps at all. But the 2013 Mercedes-Benz GLK250 BlueTEC 4Matic may just be the tipping point, a vehicle that combines enough refinement and fuel economy to make diesel vehicles a regular consideration for the American car buyer.
The GLK-class slots in as Mercedes-Benz's smaller SUV, coming in about a foot shorter than the M-class. However, the funny thing about SUVs is that the majority only seat five passengers, even when they take up two parking spaces and need a football field to make a u-turn. The GLK-class, with its upright, boxy cabin, offers a spacious interior, although cargo space is down to 23.3 cubic feet, 15 less than that of the M-class.
Mercedes-Benz offers the 2013 GLK-class with a 3.5-liter V-6 gasoline engine or, as the GLK250, with a 2.1-liter four-cylinder diesel engine. Thanks to twin turbos, this little diesel engine generates 200 horsepower and 369 pound-feet of torque.
Don't expect that big torque number to result in four-wheel burnouts with the standard all-wheel-drive system. Not only was there a little turbo lag on take-off, peak torque comes between only 1,600 and 1,800 rpms. When I stomped on the accelerator, the GLK250 set off with reasonable attention, experienced a minor rush from the turbos, then continued its pace, hitting 60 mph from zero in just under 8 seconds, according to Mercedes-Benz's numbers.
That's about one and half seconds slower than the gasoline version GLK350.
And while Mercedes-Benz does a good job of masking the clatter of the diesel engine, it isn't wholly tuned out. From the cabin, I could always here the diesel injectors pounding away as an undertone, more noticeable when idling or at slow speeds, of course. Along with the clatter was a faint odor, not the tarry smell of diesel straight from the pump, but something more like a pool cleaner.
The mild scent was likely due to the exhaust clean-up system, which relies on a urea-based liquid called AdBlue. This exhaust system incorporates an AdBlue tank, which will require refilling about every 10,000 miles.
Here's the why
Given the slower acceleration, extra noise, and added maintenance for the GLK250 over its gasoline counterpart, and that they are priced similarly, you might be wondering why Mercedes-Benz offers the diesel version at all. The GLK250's secret weapon is its fuel economy, which came in at an average of 31 mpg in my week of testing.
The car's EPA numbers registered at 24 mpg city and 33 mpg highway, but when monitoring the trip computer, I saw the average mpg holding around 35 mpg at freeway speeds. During city driving, even in the torturous traffic and up the steep hills of San Francisco, I did not notice a precipitous drop in fuel economy. After putting the GLK250 through its paces, I believe that in most areas it should easily maintain a low 30 mpg average, putting it almost 10 mpg better than its gasoline counterpart.
In many other respects, the GLK250 feels similar to the GLK350. With its fixed suspension, the ride remains firm, and well-engineered components competently deal with potholes and bumps, limiting lean and oscillation. The SUV damped the majority of the shock from hitting big potholes.
The GLK250 uses an electric power steering system, but Mercedes-Benz tuned it for a natural feel. There was no overboosting or electric whirring sounds -- the steering was responsive and the wheel had a comfortable amount of heft. This small SUV also had a decent turning radius, making it easy to maneuver in parking garages.
Along with the all-wheel-drive system, the GLK250 comes standard with a seven-speed automatic transmission. Mercedes-Benz puts paddles behind the steering wheel for manual shift mode, but like wings on an ostrich, these will see little actual use. The GLK250 seems designed for those who want to pay little mind to operating the car. It is by no means sporty, and the transmission did a fine job in automatic mode of applying lower gears when I hit braked on a hill descent.
One quirk of diesel engines is that they run at lower speeds than gasoline engines. The redline in the GLK250 was 5,200rpm. When I did try the paddle shifters for acceleration, I could barely keep up with the necessary gear changes before hitting redline.
Mercedes-Benz includes a button marked E/S on the console, which toggles the GLK250 between economy and sport modes. The switch affects the throttle tuning, but seems like a legacy from the gasoline version -- it made very little difference in feel with the diesel engine. Given the slower acceleration and shorter power curve, there just isn't a lot of room for sport mode. The typical buyer for the GLK250 will likely never bother with sport mode or mess with manual shifting.
While comfortably tooling down the freeway, enjoying the excessive fuel economy, I noticed a couple of ergonomic issues. First of all, while silver fonts on a gray background may look nice in a design studio, the theme sucks for a speedometer. Glare frequently made it impossible to read my speed, especially when I wore sunglasses. An an antidote, the GLK250 sports an LCD in the center of the speedometer, which can bet set to show a digital speed readout.