Diesel engines are engaged in the automotive equivalent of the one-armed pushup. But they're getting stronger all the time and intend to double up.
They're proliferating rapidly in passenger cars as old consumer impressions and prejudices fade away, though slowly.
General Motors, no longer smarting from its disastrous dance with diesels back in the 1980s, recently introduced a diesel in its Chevrolet Cruze compact. The Jeep Grand Cherokee SUV has a diesel model, along with the Ram 1500 light duty pickup truck. Japan's Mazda also has a diesel ready for its midsize 6 sedan.
So far -- and for the immediate future -- German manufacturers dominate the niche. Volkswagen has diesel options in nearly all of its models. Audi is the same, and Mercedes-Benz now offers diesels in its E-Class sedan as well as its MLK, ML and GL sport utility vehicles. Even Porsche and BMW have diesels in their lineups.
Despite diesel fuel prices taxed higher than regular gasoline and a scarcity of fueling pumps, diesel cars now provide the most direct competition to popular gasoline/electric hybrids like the Toyota Prius and Ford C-Max. Pure electric cars are still in their infancy, and plug-in hybrids have yet to win broad acceptance.
A powerful new V-6 diesel makes its debut in four of Audi's 2014 luxury vehicles, all of which bear a TDI badge to identify them as oil burners. TDI originally stood for turbocharged direct injection.
Two -- the A6 and A8 -- are four-door sedans; one, the Q5, is a crossover utility vehicle. The last, the superb A7, is a hatchback, though to call it a hatchback is borderline disrespectful.
The A8, Audi's near-$100,000 top-of-the-line sedan, already had curtsied to the customers when the company staged a diesel centric event in Washington, D.C., to introduce the other three and tout the advantages, stumbling blocks and rosy future of diesel engine technology.
There is little argument over the advantages. Diesel engines, which use high compression instead of spark plugs to fire the fuel/air mixture inside the cylinders, deliver 25 to 30 percent higher fuel economy, on average, than gasoline engines. Because they must be built stronger, they also last longer, which is why they power the nation's backbone haulers, the long-distance semitrailer trucks.
But because they are stronger and last longer, diesels are more expensive. In passenger cars, the premium is around $2,000.
That doesn't much matter with the new Audi models, which carry prices north of $50,000, where a couple of grand doesn't get noticed. More important, as good as these vehicles are -- and they are extremely good -- they must still motor up a steep hill of prejudice.
Most Americans still think of them as smelly, noisy, slow, dirty and impossible to start in cold weather. Only the smelly part still is true, and that's only when you stand at the pump to refuel.
All the rest is gone. In truth, few drivers would be able to distinguish any of the Audi diesels from their gasoline counterparts. The only clue inside is the tachometer, which tells at a glance that the diesel does not reach the high revs typical of a gasoline engine.
That's because diesels develop their enormous torque, or twisting force, at low rpms, which makes for a forceful jump off the line at stoplights. Of course, that also means more leisurely cruising and passing.
Take the tested A6 TDI, which is as fine a mid-sized sedan as you can find anywhere. It competes as a luxury car, which means it's not cheap at $58,395. That includes Audi's proven Quattro all-wheel drive and an eight-speed automatic transmission with Tiptronic manual shift control. With options, it checked in at $67,295.
But it was slick, quiet and comfortable, though with a sport-oriented stiff and sometimes punishing ride. Supportive front seats and outboard back seats coddle the vast majority of adults relatively comfortably on long trips. Forget the middle seat, however, which is a hard, narrow cushion against a giant floor hump. It's suitable only for backpacks or watermelons.
With its 240-horsepower, 3.0-liter six-cylinder diesel, the A6 registers 24/38/29 mpg on the EPA's city/highway/combined fuel consumption cycles. That's remarkable in a two-ton sedan.
One of the gripes at the Audi diesel symposium was that oil burners get no respect. Electrics get tax breaks, and hybrids and plug-ins often can use express lanes. Diesels must fend for themselves.
However, as Audi demonstrates, virtue eventually will be rewarded.
Model: 2014 Audi A6 TDI four-door sedan.
Engine: 3.0-liter six-cylinder diesel, turbocharged, 240 horsepower.
Transmission: Eight-speed automatic with manual shift mode and all-wheel drive.
Overall length: 16 feet 2 inches.
EPA passenger/trunk volume: 97/14 cubic feet.
Weight: 4,178 pounds.
EPA city/highway/combined fuel consumption: 24/38/29 mpg.
Base price, including destination charge: $58,395.
Price as tested: $67,295.