Mercy sakes alive, looks like we got us a convoy. Not of cab-over Petes and Kenworths haulin' logs, but a procession of Mercedes-Benz diesels strung out across the American Southwest. Near Las Vegas, more precisely, where Mercedes-Benz was holding the introduction of its E320 Bluetec luxury sedan.
Curiously, nowhere in this car's designation does the word "diesel" appear, because when it comes to unloading the baggage associated with these compression-ignition engines, Mercedes is as eager as the head bellhop at the Ritz-Carlton.
"Diesels are smelly, they clatter incessantly, are slow and belch soot," critics are wont to say. Let's take these accusations one by one and see how this new Benz fares.
Well, diesel fuel itself is stinky and oily, especially when you spill some on your pants or shoes and it wafts through the cabin. Yet what comes out of the E320 Bluetec's tailpipe is not the least bit objectionable.
Noise? On cold start, there's a faraway clatter for the first few seconds. After that, you'd be hard-pressed to tell it's a diesel with the windows up and, say, the ventilation fan blowing on its low setting. And ultra-quick piezoelectric injectors spritz what Mercedes calls a pilot charge into the combustion chambers milliseconds before the main dose of fuel, smoothing out pressure and temperature spikes and reducing the "marbles in a coffee can" sound so beloved by UPS drivers.
Slow? Hardly. This new 3.0-liter V-6 (despite what the E320 designation might have you believe) is intercooled and turbocharged, with the exhaust-stream hamster wheel made more responsive with a variable-vane arrangement similar to what's used on the Porsche 911 Turbo. This steel-sleeved, aluminum-block engine makes 208 bhp and an axle-twisting 388 lb.-ft. of torque-the last stat nearly matching Mercedes' 5.5-liter gasoline V-8-on tap from 1600 to 2400 rpm.
Mercedes isn't offering acceleration numbers, but we'd guess that 0-60 times are in the high 6-second range. All that torque is applied through a 7-speed automatic with Touch Shift sequential shift ability. Significantly lighter and more compact than the cast-iron-block inline-6 it replaces, the Bluetec diesel can (and does, at least in Europe) power everything from a C-Class sedan to a Jeep Grand Cherokee. As sooty as a chimney sweep? Not a chance, benzene-breath. The Bluetec's exhaust has to pass through a phalanx of devices: an oxidation catalytic converter snugged up against the turbo's exit, the NOX storage catalyst, a ceramic particulate filter, and a third converter near the tailpipe. The particulate filter is especially interesting, as it periodically undergoes what's analogous to a self-cleaning oven cycle as it becomes clogged with soot. On cue from the engine-management computer, extra fuel is injected, dumping more unburned hydrocarbons into the first converter to increase heat; also, the timing of injections is retarded. Both result in the exhaust temperature briefly hitting 650 degrees Celsius (more than 1200 degrees Fahrenheit), enough to burn off the soot and clean the filter.
Although EPA figures are not finalized, the E320 Bluetec achieves roughly 27 mpg city, and 36 mpg highway, for a combined number of 30 or 31. Consider its 21.0-gal. tank and you've got an Interstate cruising range of more than 700 miles. Better yet, the $52,325 Bluetec is just $1000 dearer than its equivalently equipped E320 gasoline counterpart, so it's possible to amortize that additional cost with fuel savings over two years or so. Do the math with many popular hybrids, and the time frame can be multiple decades, far longer than most people keep a car.
2007 Mercedes-Benz E320 BlutecSo what's the downside? Well, it accelerates nicely, but the throttle response seems a little muddy, with a lot of pedal travel required to get the desired result. Right now, the Bluetec is a 45-state car, but when the EPA decides on the particulars of urea injection-which cuts NOX production even further-it will meet the more stringent regulations of the Californias and New Yorks of the world. Diesel fuel still can't be found at every filling station…but the optional nav system will point you to the nearest pump with the required LSD (Low Sulfur Diesel), which has been on sale since October 15, 2006. Just goes to show that "diesel" is not a four-letter word…it's six at last count.
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