Can a diesel be the Ultimate Driving Machine?

[Jonathan Spira]

If you still think that diesels are slow and noisy, and belch black smoke, you’re not alone—but you probably live in the U.S. Today, diesels in Europe account for roughly 50% of the market. In BMW’s home market of Germany, 70% of BMWs sold are diesels.

The BMW X535d

But in the United States, the market is minuscule, in part because diesel automobiles acquired a reputation for poor reliability thanks in part to diesel models from Cadillac and Oldsmobile in the 1980s. For some reason, the ultra-reliable Mercedes 240d never seems to be what comes to mind, despite the fact that these cars were typically able to last well over 100,000 miles. (Of course, getting one to start at 40 below was an interesting adventure. . . but what’s life without a little challenge?)

Today, however, diesels are staging a comeback in the U.S., thanks in part to low-sulfur diesel fuel. BMW is part of this movement, accompanied by Audi, Mercedes-Benz, and Volkswagen. BMW enthusiasts began to take note of diesels last year when BMW announced plans to offer 50-state diesel-powered BMWs (namely the 3 Series and X5), promising no compromises in handling and performance. Anyone who has driven a modern diesel knows of its advantages over gasoline. Diesels use far less fuel—about 30% less on average than their gasoline-burning counterparts—and emit 25% less carbon dioxide. They also produce 50% more torque, which translates to higher acceleration at lower rpm.

But until about ten years ago, Europeans, too, were happy to relegate diesel technology to trucks, buses, and taxis—a common assignment for the Mercedes 240d. But that changed around 1997, when Bosch introduced the common-rail injection system, where diesel fuel is precisely injected at a very high pressure (much higher than in a gasoline engine). Its name derives from the one common fuel-feed pipe—or rail—that provides fuel for all injectors. The common-rail system reduces exhaust emissions and lowers engine noise, thereby ameliorating the two most common objections to diesel-powered automobiles.

To see what’s changed, I spent over a month driving four diesel-powered automobiles: BMW’s 535d, the Audi A6 TDI, the Volkswagen Jetta TDI, and the Mercedes-Benz ML320 BlueTec. I also spent a few hours behind the wheel of a BMW 335d and a 123d. Here’s what I found.

The BMW 535d is not available on these shores. . . yet.

BMW 535D
With its three-liter inline six-cylinder engine with two turbochargers (a small one for low revs, large for high revs) that work in sequence to eliminate turbo lag, the 535d has so much power that you simply would have had to look at the model badge on the trunk to confirm it’s a diesel. BMW even engineered the exhaust note to sound like a gasoline-powered BMW straight six. And it’s not dirty or smelly, either; the tailpipe had no soot stains that would betray its humble origins.

In the five days I had the car, I drove a total of 1,126 kilometers (700 miles), including a round trip from Munich to Vienna, averaging 40 mpg (5.9 liters/100 km). On a clear stretch of Autobahn outside Munich, the car happily stayed at 240 kph (150 mph), traffic permitting. In Austria, I tried hard to stay below 150 kph (93 mph) because the photo radar on the Autobahnen are set for that speed—but it was difficult not to accelerate to the car’s full potential. Fortunately, the photo-radar units are quite visible during the daytime.

While the 535d won’t be offered in the U.S.—at least not right away—BMW is now importing the 335d, which uses the same engine in the smaller 3 Series body.

The BMW 335d is now available at your local BMW dealer.

BMW 335d
I only spent a few hours in this car, but all I can say is, “What torque! What torque!” Just like the 535d, the 335d has sick amounts of torque and provides bone-crushing acceleration devoid of any turbo lag. There’s no question in my mind that this car will establish the BMW diesel line in the mind of the enthusiast. Rated by the EPA at 23 mpg in the city and 36 mpg on the highway, it is the most fuel-efficient car BMW has ever sold in the U.S. And even a short drive reveals that there is no question that BMW kept its “no compromises in handling” promise.

The 335d will have a list price of $44,725, including destination and handling, and is eligible for up to a $900 IRS Alternative Motor Vehicle Credit. (The X535d has an MSRP of $52,025, also including destination and handling, and is eligible for a maximum tax credit of $1,550.)

As easy as 1-2-3: the BMW 123d

BMW 123d (three-door)
Admittedly, I only got to spend half an hour in this car, but it was a brilliant 30 minutes. The twin-turbo 123d aluminum four-banger produces 204 horsepower and 295 pound-feet of torque at 2,000 rpm—enough to get this car from 0 to 62 mph in 7 seconds. Fuel consumption is rated at 49 mpg on the highway. That’s not a typo!

THE COMPETITION

AUDI A6 TDI
During four days with the A6, the fuel gauge barely moved—despite my having driven over 150 miles. While I didn’t get a chance to test the car’s top speed (153 mph, compared to the gasoline engine’s 155), I did have plenty of opportunities to test the car on a variety of roads. The engine’s 332 pound-feet of torque (50% more than the gasoline version) made driving (and overtaking) a pleasure. I consistently got 22-24 mpg in town and up to 40 mpg on the highway. (This car is not available in the U.S.)

MERCEDES-BENZ ML320 BLUETEC
The second-generation M-Class has been refreshed for 2009, and a new 50-state diesel power plant has been added. It was also the only diesel that didn’t aspire to the 40-mpg mark, with only 24 mpg on the highway—although this is far better than other SUVs. In mostly city driving, I averaged 18 mpg. (The X5 diesel is rated at 19/26, incidentally, and does 0-60 in 6.9 seconds compared to the ML’s 8.0.) Passing slower vehicles on a highway required planning ahead, as the engine’s power peaks at 2,400 rpm.

VOLKSWAGEN JETTA TDI
On a round-trip journey to Philadelphia from New York City, the Jetta averaged 43 mpg on the highway, with speeds ranging from 55 to 80 mph. The Jetta provided a steady supply of power with just a hint of turbo lag, and its torque made passing easy. The easiest thing about the Jetta is its price: $22,000 for a 40-plus-mpg non-hybrid. It’s nicely equipped at that price, too, with comfortable heated seats and high-quality materials in the cabin.

So there you have it: a quick comparison of some of the oil-burners out there, including the new BMW. One thing's for sure: It's definitely not your father's (diesel) Oldsmobile! —Jonathan Spira, technology editor, bmwcca.org