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The New Truth About New Diesel.

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Despite lower prices for clean diesel fuel, perception of diesel vehicles has not kept pace with the technology.

Differences between American and European automotive tastes are particularly notable when it comes to diesel-powered automobiles. Europeans love them, and have for years, partly because of their greater fuel economy on a continent long plagued by high fuel prices.

2010 Mercedes-Benz R320 CDIU.S. vs. Europe Diesel Market.

Americans may not hate diesels, but we're clearly wary of them. Diesel proponents thought widespread availability of "clean" (low-sulfur) fuel would spark renewed interest. Yet, only four automakers currently sell diesel-engine cars in the U.S. Half a dozen others had planned to make diesels available, including Honda, Nissan and Toyota (as well as the domestic companies). Most were aimed at light trucks, including Ford's F-150 and the Dodge Ram; but several were under consideration for passenger cars. By mid-2009, however, each manufacturer had second thoughts about diving even modestly into diesel power.

Diesels stabbed at the U.S. market in the late 1970s. What mainly killed diesel power back then were General Motors' dubious offerings. Rather than develop a true diesel engine, engineers took GM's existing 350 cubic-inch (5.7-liter) gasoline V-8 and converted it to run on diesel fuel. Between 1978 and 1985, diesel V-8s were installed in various models of all five GM brands. GM also offered a diesel V-6. Even the little four-cylinder Chevrolet Chevette could go diesel. U.S. automaker diesel offerings for North American customers are currently limited to full-size pickup trucks. Ford's new Fiesta ECOnetic gets 65 mpg-not on U.S. roads, though.

U.K. Ford Fiesta ECOneticEuropean-brand automakers turned to diesel power far earlier. Mercedes-Benz issued its first diesel-powered 170 sedan in 1948, and diesel-engine models soon trickled into the U.S. Diesel equivalents of popular import models emerged in the 1980s, from Volkswagen, Datsun/Nissan, Mazda, Volvo, and Toyota. Only Volkswagen and Mercedes-Benz have continued past the 1990s.

Vehicles with American-made diesel engines, in particular, wound up with notoriously poor resale values. Anyone who's heard the raucous clatter of an aging GM diesel V-8, sending its jarring, discordant melody to ears hundreds of feet away, isn't likely to have a favorable view. Early diesels also developed a reputation for sending out soot and black smoke, as well as emitting noxious odors.

Over the past decade, auto-industry executives and automotive journalists have sung the praises of diesel engines, attracted by their impressive fuel economy as well as their strong torque output, which can translate to energetic acceleration. As soon as "clean" fuel became readily available, they predicted, a new world of diesel power would be upon us.

2010 Audi A3 TDIGerman Engineering Equates to Clean-and Green.

That hasn't happened as quickly as anticipated. The federal government has mandated ultra low sulfur fuel since 2007. German automakers, Audi, BMW, Mercedes-Benz and Volkswagen, have led the parade toward modern diesel power. In fact, Volkswagen's clean diesel Jetta TDI sedan (lead photo; Street Edition trim shown) won Green Car of the Year honors for 2009 and Audi was awarded the same prize for its 2010 A3 TDI 5-door hatchback wagon.

After abandoning diesels in 2000, Mercedes-Benz returned several years later with the E320 CDI sedan. Since then, several additional models have emerged. The 2010 lineup now includes three newly revealed models: the ML320 CDI, a mid-size sport utility, the R320 CDI, a six-passenger touring car, and the E320 BlueTEC, a full-size luxury sedan. When Mercedes-Benz redesigned its E-Class sedan for 2010, each model had a gasoline engine, but diesel equivalents are coming in spring 2010.

2010 BMW 335dVolkswagen's diesel history began with the late '70s Rabbit, continuing past the end of the century. For 2009, after a two-year absence, VW introduced its first model to take full advantage of the new "clean" (low-sulfur) diesel fuel: the Jetta TDI sedan and wagon. The 2.0-liter TDI four-cylinder engine develops 140 horsepower and 236 pound-feet. With manual shift, the diesel Jetta yields a fuel-economy estimate of 30 mpg in city driving and 41 mpg on the highway. A six-speed automatic transmission drops those figures by only 1 mpg. Volkswagen claims, with considerable justification, that careful real-world driving can boost those mileage estimates considerably.

Gasoline-engine Jettas manage no more than 31 mpg. Volkswagen also offers its Touareg sport-utility vehicle in turbodiesel form, with a 3.0-liter V-6. Fuel economy is estimated at 17 mpg city/25 mpg highway, versus 14/20 mpg for a Touareg with a 3.6-liter gas engine.

For 2009, Audi launched a diesel version of its big Q7 sport-utility vehicle. Its 3.0-liter, 221-horsepower turbodiesel V-6 yields a healthy 406 pound-feet of torque. The TDI edition gets a fuel-economy estimate of 17/25 mpg (versus 14/20 mpg for gasoline).

BMW launched its first diesel-engine passenger car, the 335d sedan, for the 2009 model year. The 3.0-liter twin-turbo diesel inline six-cylinder develops 265 hp and an enthusiast-satisfying 425 pound-feet, for a fuel-economy estimate of 23/36 mpg (far beyond the 17/26 mpg estimate for a gasoline equivalent). BMW also made the 3.0-liter diesel engine available in its X5 crossover SUV.

Critics advise that diesel-engine models cost more than gasoline vehicles, because additional components are needed in each vehicle. True enough, though the difference isn't always great-and may easily be offset by reduced fuel costs. Volkswagen's Jetta TDI has a suggested retail price of $22,970 (including destination charge), versus $18,215 for the least-costly gasoline model. BMW asks $44,725 for the diesel-engine 335d sedan, and $41,125 for its 335i gasoline equivalent.

2010 Jetta TDI SportWagenClean Diesel Availability.

Though 50-state diesels soon will be the norm, a few remain unavailable in several states with stricter emissions requirements. Not every service station that sells diesel fuel has the correct ultra-low-sulfur (ULSD) variety, either. Until 2010, retailers (except in California) are permitted to sell the older diesel fuel, which could cause grave damage to an engine designed for "clean" fuel. Though more stations sell diesel fuel these days, it can still be tough to find in some areas.

In addition to public wariness, fuel prices have been too low lately to make the more thrifty-running diesel models sufficiently attractive. In summer 2008, diesel fuel pushed toward $5 a gallon. A year later, it was going for around $2.60 per gallon, a hair below the cost of gasoline.

Diesel advocates claim noise and soot are virtually nonexistent in the modern diesels. Yet, many shoppers seem ready to say "no" if they detect a whiff of odor or slight engine clatter.

Despite the hesitation exhibited by most manufacturers, Volkswagen has earned strong sales with its latest Jetta TDI model. During June 2009, TDI diesels accounted for 40 percent of Jetta sedan sales, and 81 percent of Jetta SportWagens. Mercedes-Benz, too, does well with its multi-model diesel lineup.

A mid-2009 TV commercial from Audi insisted that diesel "is not a dirty word." Except for fans of those VW, Audi, BMW, and Mercedes-Benz diesels, not many Americans appear to be getting the message.

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