Mercedes-Benz kicked off the race to the finish line for 50-state legal, urea-injected diesels this week with a first drive in Vermont. Mercedes chose Vermont for the international media debut of its BLUETEC diesel SUVs for the scenic vistas and the fact that the Green Mountain state is one of the states that has chosen to enforce California emissions standards. Those emission standards are by far the tightest in the world, particularly when it comes to diesel engines. The Tier 2 Bin 5 standard regulates emissions of nitrogen oxides to one fifth the level of the upcoming Euro 5 emissions standards.
A whole new batch of T2B5 compliant diesel-powered vehicles are on their way to U.S. car dealers starting this summer with the VW Jetta TDI. Mercedes aims to beat BMW to market with larger diesel vehicles. The existing ML320, GL320 and R320 CDI models are only available for sale in 45 states. The CDI models are being replaced for 2009 by BlueTec models that add selective catalytic reduction (SCR) after-treatment systems to the existing particulate filter and oxidation catalyst. Mercedes is already the first manufacturer to get T2B5 certification. Read on after the jump to find out how they behave on the road.
Photos Copyright ©2008 Sam Abuelsamid / Weblogs, Inc.
Upon landing at Albany International Airport in New York, the gathered media checked in with Mercedes and Car and Driver's Larry Webster and I set out in a silver R320 BLUETEC for the 60-mile drive to Manchester, Vermont. The R320 is one of the three vehicles that Mercedes builds at its factory in Tuscaloosa, Alabama. The others are the ML and GL SUVs. Mercedes refers to the R-Class as part of its SUV lineup but if anything it's most like one of the classic American full-size station wagons that mostly died out in the mid-seventies. In today's automotive landscape, it would fall into the crossover class with vehicles like the new Ford Flex and the departed Chrysler Pacifica.
The R320 sits lower than its siblings on a longer wheelbase that makes the third row seat fairly usable, at least for shorter trips. The R320 features a panoramic moon roof that takes up most of the roof. Since its introduction for 2006, the R-Class styling has always been controversial and it remains unchanged for 2009 as does the big GL320.
The ML320 has gotten a bit of a mid-cycle facelift for 2009 that primarily consists of a revised grille and headlights and interior upgrades. All three vehicles consist of a unit-body architecture with power being transferred to the ground through all four wheels via Mercedes 4Matic full time all wheel drive system and a seven speed automatic transmission.
However, all of this is ancillary to the real reason we came to Vermont: BLUETEC diesel engines. The 3.0L V6 diesel itself is largely carried over from the existing CDI powerplant including the 72 degree aluminum block. Helping to resist the pressures that build up in the diesel combustion chamber are cast-in iron cylinder liners. The latest piezo electric fuel injectors sit in the center of the four valves in each combustion chamber while a throttle plate in one of the two intake ports of each cylinder help to improve the air flow in the other port at light load conditions. This last element is unique in that diesel engines typically have no throttle, engine power and speed being controlled by fuel flow.
The 23,000 psi common rail system with the piezo injectors helps to optimize the fuel delivery, reducing fuel consumption and emissions. The injectors can provide up to seven pulses per ignition cycle, spreading out the pressure build over the course of the power stroke. In this way combustion temperature and pressure build rates are reduced, and there is lower production of NOx and noise.
On the road, the BLUETEC SUVs don't feel noticeably different from their gasoline-powered counterparts. As with other modern diesels, these are nearly as quiet as the gas engines and operate just as smoothly. Pressing the start button on the dash behind the right side of the steering wheel, causes the engine to fire instantly and quietly.
Mercedes uses a single turbo configuration on its six cylinder diesel in contrast to BMW. BMW's dual turbo setup yields 265hp and 425lb-ft while the Mercedes engine only produces 210hp and 398lb-ft. In spite of that lower power figure, the ample torque proves up to the task of motivating the Alabama-built trio. The BLUETEC trucks won't be challenging the high-output AMG variants in drag race but a 0-60mph time of 8.0 seconds for the ML320 to 9.1 seconds for the heavier GL should meet most drivers' needs with ease. For those that need to tow, the 3.0L diesel offers the same 7,500lb towing capacity as the 4.7L V-8 gas-powered GL450.
Where the BLUETEC-powered vehicles don't match their gasoline counterparts is in fuel economy. Here there is simply no comparison. Mercedes offered up a fleet of the three vehicles with several routes pre-programmed into the navigation system. I sampled each model on a route that included some low speed driving in Manchester and Arlington, Vermont as well as the rural roads in the area. For each vehicle I reset the mpg readout before heading out.
Along the route I stopped to do some photography and left the engine running while shooting and moving the vehicles around. The R320 recorded 23mpg, while the GL managed 24mpg and the ML got 27mpg. While this was a short loop of only about 20miles, those are still some impressive numbers. Even more impressive was the result I got on the return trip from Manchester to the airport in Albany. On a seventy-mile drive the ML320 BLUETEC ended up with 29.5mpg!
I didn't attempt to do any hypermiling to achieve these numbers, just basic common sense driving. While generally avoiding jack-rabbit starts, there was some on-ramp acceleration to get on the highway and some stop and go through several towns on the route. The gas-fueled ML350 is rated 15/20mpg city/highway by the EPA and 17mpg combined. Even with gas and diesel at $4.20 and $5.00 respectively, driving an ML320 at 27mpg will yield savings of $746 a year.
Mercedes only charges a $1,000 premium for diesel engines over the base gasoline version and plans to maintain that differential in 2009. Even with the diesel price differential as it is today, the payback would be less than 18 months. Furthermore, the 2008 GL320 CDI is similar in size to a Chevy Tahoe hybrid and runs about the same price at $53,400 (not including the recent $4,000 rebates GM started on its hybrids).
Aside from the diesel the rest of the drive was pretty uneventful. The Mercedes SUVs have very well appointed interiors with rear seat DVD systems and navigation/Sirius satellite radio system in front. The nav system doesn't have a touch screen or a control knob like BMW's iDrive or Audi's MMI. The interface is not as obtuse as iDrive but its definitely not as easy to use as Ford's latest system appearing on its 2009 models.
The ride quality was comfortable but not particularly inspiring to drivers looking for a more involved driving experience. The dampers were a bit on the soft side in their default mode with Sport mode tightening things up a bit. The steering, as in so many other vehicles of this type, was pretty lifeless with no real indication of what was going on with the front wheels.
Overall, we're looking forward to a longer sojourn at the wheel of the new BLUETEC diesels. More importantly we want to see Mercedes diesel engines in some of their cars. First up will be the new E-Class coming in 2009 with the same powertrain used in these vehicles. For those that opt for one of these when they go on sale this October, replenishing the AdBlue is something that will typically be done at the 10,000 mile service interval. The 7 gallon AdBlue tank sits below the cargo area and should hold enough to last 15-16,000 miles for almost all drivers.
Photos Copyright ©2008 Sam Abuelsamid / Weblogs, Inc.
Our travel and lodging for this media event was provided by the manufacturer.