MANCHESTER, Vermont - Enthusiasts tend to love them. Analysts suggest a possible revival. At least a few manufacturers have been busily working out the kinks. And two years ago the U.S. Government finally mandated "clean," low-sulfur fuel, paving the way for better examples.
Naturally, we're talking about diesels. As far back as the early 1960s, Mercedes-Benz stood among the leaders in the first diesel-engine revolution. In 1963, a Motor Trend writer crossed the continent, from San Francisco to New York City, in a Mercedes-Benz diesel sedan. His total fuel bill: a penny-pinching $35. Of course, that was back in the day when gasoline cost only 30 cents a gallon, and diesel probably cost even less.
By 1982, after two oil crises drove up the cost of fuel, Mercedes-Benz had captured an 80-percent share of the diesel market in the U.S. In that same era, Volkswagen offered a batch of diesel-powered automobiles. So did a handful of other import brands. And so did General Motors - with far less success.
In fact, GM often is credited with helping to "kill" interest in diesel power, because its diesel V-8s were so awful. There was a reason for their poor operational quality, however. GM's V-8s weren't really diesels at all. They were essentially regular gasoline V-8s, converted into a diesel configuration. The lesson finally learned: trying to transform an engine designed to work on gasoline into a diesel - which operates at far tighter compression within each cylinder - doesn't work.
By the 1990s, diesel popularity sagged drastically - though they remained highly popular in Europe and elsewhere in the world.
In 2006, Mercedes-Benz led a comeback of diesel power with the E320 BlueTEC sedan - an E-Class model with a diesel six-cylinder engine. One drawback: like other diesel models on the market, it could not be sold in California and other states with especially rigorous emissions standards. Before long, 7 percent of E-Class sedans sold in the U.S. ran with diesel power.
Now, for 2009, Mercedes-Benz is moving ahead with a new generation of BlueTEC diesel engines, available for the German automaker's three sport-utility vehicles: GL-Class, R-Class, and ML-Class. Known respectively as the GL320 CDI, R320 CDI, and newly-facelifted ML320 CDI, these diesel SUVs each hold a six-cylinder engine that produces 210 horsepower - plus a whopping 398 pound-feet of torque. That's one of diesel's advantages: torque output that exceeds by far what a comparable gasoline engine can generate. As a result, said R-Class, SUV Hybrid and BlueTEC director Thomas Ruhl, buyers will get "V-8 performance and outstanding torque" from an engine with six cylinders.
Another diesel advantage is better fuel mileage than gasoline offers. Mercedes-Benz advises that when installed in an ML-Class or R-Class vehicle, the BlueTEC diesel gets an estimate of 24 mpg for highway driving.
Of the three SUVs that are getting the new, "cleaner" diesel engines, the R-Class and GL-Class are largely carryovers for the 2009 model year. Mercedes-Benz's ML-Class gets a modest facelift, whether in gasoline or diesel form.
When you have to open the door and lean your ear toward the engine to hear even a trace of diesel "knock," it's evident that Mercedes-Benz has brought diesel power into a new realm. Perhaps this time, it's truly ready for mass marketing, through all 50 states.
The facelifted ML320 CDI is particularly pleasant and easy to drive, with lighter handling than some M-Benz models. Virtually no evidence of diesel power exists unless you stand outside and listen closely. Response may fall short of stirring, but it's wholly adequate for ordinary driving and often more so
A GL320 CDI seemed a tad more sluggish when tromped at 35-45 mph - though again, wholly adequate - but more eager and energetic at lower speeds. Slightly more diesel sound can be heard, but it's barely discernible with the windows up. Handling with a heavier feel than ML, the GL320 feels a little stiff on the road, and even exhibits a slight touch of floatiness at times. Here too, everything is smooth and refined.
Response is less stimulating in the R320 CDI; but here too, few drivers will feel it's underpowered. Though easy to drive, the R-Class feels markedly bigger than its mates. Even with the window open, only slight diesel sound can be heard.
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