Mercedes GLK250 BlueTEC 4MATIC: Bringing Diesel Tech to a Midsize SUV

Gary S. Vasilash

Mercedes has been putting diesels in vehicles since 1926. It has been offering them in the U.S. since 1949. And 2013 is seeing a range of offerings, including in its popular GLK SUV.

Peter Lückert’s title is director, Diesel Powertrain Development.

If Lückert worked at most automo-tive companies, that would be like carrying a card analogous to “Repairman, Maytag Corp.”

But Lückert doesn’t work at most automotive companies. He works at Mercedes-Benz. And at Mercedes, they take diesel engines rather seriously.

In recent times in the U.S.*, Mercedes has offered a variety of diesels. Staring in model year 2007, it began offering a V6 diesel (replacing the in-line configuration that it had long had on offer) with common-rail direct injection (CDI). This CDI engine was the first ULEV diesel; the 215-hp, 398 lb-ft diesel was available as the ML320 CDI, GL320 CDI and R320 CDI, all SUVs (with the R-Class being an SUV of a sort).

2007 also saw a world-wide introduction in the U.S., the E320 BlueTEC diesel, a 210-hp, 398-lb.-ft. engine that features after-treatment technology that made it 50-state compliant (meeting BIN5 NOx and particulate limits).

Then the even cleaner diesel was launched in 2009, when the AdBlue exhaust gas after-treatment system was made available on the ML320 BlueTEC, GL320 BlueTEC, and R320 BlueTEC, with the “320” being the same V6 turbodiesel found in the E320 BlueTEC, but in this case, the engine had gone from the sedan to the SUV lineup. In 2010, the Sprinter commercial van was offered with a 3.0-liter V6 diesel providing 188 hp and 325 lb-ft.

And they’ve just launched the OM 651 BlueTEC diesel, a 2.1-liter four, in the 2013 GLK-Class. (And perhaps by the time you read this, there will be the same engine under the hood of the 2012 E-Class.) In the SUV, the engine produces 200 hp and 369 lb-ft of torque.

Clearly, Lückert hasn’t had a whole lot of time on his hands.

The BlueTEC approach to handling the emissions of diesel engines is both straightforward and clever. Mercedes starts with a diesel oxidation catalyst that handles carbon monoxide and hydrocarbons. There’s a catalytic converter to process nitrogen oxide—but this is not necessarily capable of dealing with all of it. There is a particulate filter that collects the “soot” (when the filter is filled, then this is burned out of the filter). Then there is the SCR—the selective catalytic reduction catalytic converter. This is where the AdBlue comes into play, a liquid consisting essentially of urea and water (tinted blue, sort of like windshield washer fluid). This is injected into the exhaust gas and this ammonia (NH3) converts the NOx into nitrogen and water.

Lückert says there are several aspects of making the diesel powertrain setup in the GLK250 BlueTEC 4Matic highly efficient. One is to reduce internal engine losses. So they are using roller bearings for the Lanchester balance shafts. There is an adjustable oil pump to reduce hydraulic losses. They have increased the thermal efficiency of the engine. There is a high-performance injection system; the common rail system performs at 2,000 bar. There is a switchable water pump and a switchable EGR cooler. The all-aluminum in-line four has a two-stage turbocharger system with the two turbos—a small high-pressure (HP) unit and a large low-pressure (LP) turbo—connected in series: the HP unit is located right at the exhaust manifold and the LP further along the way.

The HP turbine can rotate at up to 215,000 rpm. The LP turbo can operate at up to 185,000. The HP turbo housing has a bypass duct; the duct is opened or closed by a vacuum-operated wastegate. So when closed, all of the exhaust gas goes through the HP turbo, which makes it effective even at low engine speeds. As the engine speed increases, then the wastegate opens, thereby routing the exhaust gas to the LP turbo. 

Meanwhile, on the intake side of the system, air goes through a low-pressure compressor, compressed by the LP turbo, then to the HP turbo, for further compression. Further improving the performance of this setup is an intercooler that reduces the temperature of the compressed air by some 280°F, which means that there is a larger volume of air pumped into the combustion chamber.

All of this contributes to improved engine performance, as in high torque at low engine speeds, no turbo lag, and good fuel economy: 24 mpg city/33 mpg highway. (Of course, it should be noted that the fuel economy isn’t predicated entirely on the diesel engine; the GLK250 BlueTEC is also equipped with a seven-speed automatic transmission.)

One interesting aspect of Mercedes’ approach to this diesel offering is how it is positioned and priced in the GLK lineup. There is the base GLK350 with a 3.5-liter, naturally aspirated V6 that provides 302 hp and 273 lb-ft of torque. It is priced (absent destination charges) at $37,090. There is the GLK350 4MATIC, which adds the full-time, four-wheel drive system to the vehicle. It is priced at $39,090. Then there is the GLK250 BlueTEC 4MATIC, which is priced at $38,950. While diesel vehicles are typically priced higher than their gasoline-powered counterparts, Mercedes is taking an approach to make the diesel cost competitive with the gasoline vehicles. While the V6 provides more horsepower—302 vs. 200—the diesel four pro-vides more torque—369 vs. 273. What’s more, when it comes to fuel economy, the diesel is way ahead—24/33/28 mpg (city/highway/combined) vs. 19/24/21 mpg.

As fuel economy regulations become tighter, it is a safe bet that Peter Lückert will get a whole lot busier. 

*If you want to know when Mercedes started with diesels in the U.S., you’ll have to go back more than 60 years: in 1949 it offered a 38-hp, 71 lb-ft 1.7-liter in-line four, the 170D. That “38” is not a typo.

The 2013 Mercedes  GLK250 BlueTEC 4MATIC @ a Glance

The name is a bit packed. So briefly, this is a GLK, the smallest of the Mercedes SUVs, with the others being the G-, GL- and M-Class models. While the GLK350 has a 3.5-liter gasoline engine, the GLK250 has a 2.1-liter diesel engine, so the nomenclature isn’t 1:1. The BlueTEC refers to the after-treatment system used to clean the diesel exhaust. In the case of the GLK250, it includes the selective catalytic reduction catalytic converter, which uses “AdBlue,” a urea-based fluid, to further minimize emissions. The “4MATIC” refers to the full-time, four-wheel drive system.

Visually, compared with the model year 2012 GLK, the 2013 model has new headlamps, LED daytime running lights, front and rear bumpers, side view mirror design, and 19-in. wheel designs. Inside, there are significant changes to the IP, including a color instrument display for the center gauge, new air outlet designs, and a single piece of wood trim on the front of the IP rather than sectional pieces. The gear selector has been moved from the center console position to the steering column, which allows a larger storage bin in the center console. In addition to which, there is a new steering wheel.

The five-passenger vehicle is 178.3-in. long, has a 108.5-in. wheelbase, and is 74.25-in. wide and 66.9-in. wide. It has a curb weight of 4,321 lb.

The 2013 GLK250 BlueTEC 4MATIC. As part of Mercedes’ diesel initiative, they have put a 2.1-liter direct-injection, four-cylinder diesel engine in a vehicle that has previously been offered only with a 3.5-liter V6 gasoline engine.