Jul 2, 2008
2008 Mercedes-Benz Bluetec SUV Test Drives: Diesel Engine Offers Hope for Big Vehicles
MANCHESTER, Vermont— Maybe it’s misplaced emotion, but at times, one finds it hard not to feel a little sympathy for the car companies these days. After all, skyrocketing fuel prices have taken a big bite out of the historically profitable truck and SUV segments. Sure, small-car sales are up, but the consumer demand for more fuel-efficient cars has caught a number of automakers off-guard.
So launching a premium SUV—even one powered by diesel—takes something of a leap of faith. And the company ready to leap right now is Mercedes-Benz. Their SUVs and crossovers, the five-seater ML-Class, the seven-passenger GL-Class and the six-seater (with an option for seven) R-Class, now get the option of a 50-state-legal diesel engine: the 320 CDI Bluetec. Benz officials have faith that the high current costs of diesel is an anomaly that will right itself in good time. As diesel fans, we certainly hope so.
Across winding two-laners here, we recently put the pedal down on the full range of V6 diesel Mercedes-Benz SUVs—ML, GL and R—to find out which ones make the most compelling case for hauling capability, without instilling the fear of a lease for yet another rig with a gas-guzzling V8. —Colin Ryan
Some of us have seen this engine before—in a version of the E-Class mid-sized sedan offered for lease in California. Yes, despite the Golden State’s otherwise laid-back attitude, it’s notoriously picky when it comes to emissions. So Bluetec’s claim to be the world’s cleanest production diesel engine is pretty much on the money. How so? It starts off with clean fuel (low-sulfur diesel in this case) pumped into a common rail setup, then injected into an all-aluminum, turbocharged and intercooled 3.2-liter V6 engine. Technology has come far enough to enable a high degree of efficiency at every stage of compression and combustion. But it’s when those spent gases leave the chamber that Bluetec really comes into its own.
The catalytic converter does what it usually does, dealing with carbon monoxide and unburned hydrocarbons. Then a particulate filter captures microscopic, barely measurable pieces of soot. The final step is the AdBlue system. AdBlue is a euphemism for urea, which is more or less what it sounds like. Ammonia is the key ingredient, sprayed into the exhaust gases as they pass though an SCR (selective catalytic reduction) unit. This arrangement tackles nitrogen oxides, the one exhaust component that’s higher for diesels than for gasoline-powered engines. Eighty percent is converted into harmless nitrogen and water. Emissions are low enough for Bluetec-equipped cars to qualify for the same federal income tax credits as hybrids (these expire at the end of 2010, but, with another possible leap of faith, Mercedes hopes they’ll be extended). Anyone thinking long-term right now can rest assured: The urea tank needs replenishing every 10,000 miles or so and can be done during a routine service. The cost of the liquid is fairly cheap, but Mercedes has no exact figures at the moment.
In the ML-Class, updated for the 2009 model year, the diesel responds well, and there’s hardly a hint of traditional diesel rattle. Only when cold or when revved harder than usual does the driver become aware that this isn’t a gasoline V6. It’s all torque with diesels, so the less-than-scintillating 210 hp at 3400 rpm is more than made up for with a hefty 398 lb.-ft. of twist from the basement-low 1600 rpm.
The ML is the fastest of the three in the sprint to 60 mph, clocking in at 8.5 seconds. And it certainly feels sprightly. It’s the most enjoyable to drive, and at 4,974 pounds, it’s the lightest of the trio. Over a test run of 188 miles, through light traffic and a mix of small towns and rolling hills, we hit at an average speed of 44 mph and the ML returned 27.5 mpg.
The GL is, in essence, a bit of a “yank tank.” It’s a big SUV, best enjoyed with the cruise control activated and eating up the miles on a family road trip. Over 101 miles, averaging 38 mph, the GL achieved 25.8 mpg. But in this application, the V6 starts to feel a touch overwhelmed by the GL’s extra mass.
It’s a similar story with the R-Class, although consumption doesn’t seem to suffer by much. Covering 58 miles at an average of 39 mph resulted in 27.4 mpg. This vehicle falls somewhere between the categories of minivan and SUV—it’s really a long, tall wagon, smooth and sedate. But if we’re honest, the interior seems a little too nice to let a young family loose on it.
The Bottom Line
A Bluetec engine can be 25 to 33 percent more frugal than a similar-displacement gasoline engine. The ML and the R 320 CDI should start around $45,000 and $43,000, respectively, when these models arrive in October. That’s $1,000 more than the 3,5-liter gasoline V6 counterparts. Coupled with high fuel prices, these machines make the most sense if someone is doing higher-than-average mileage on mainly freeway routes. Since there isn’t a comparable V6-powered gas equivalent in the GL, then this Bluetec version will be about $3,000 less than the smallest V8 model (the GL450, currently starting at $55,900). Any family whose environmental conscience and checking account are conspiring to turn them away from SUVs may soon start seeing these Blutecs as a viable option.