Power to the Diesels

BMW wants you to know it's paying attention. As a company whose cars are aimed at people who enjoy performance driving, it may leave some consumers feeling that it's out of step with all things green.

Munich-based Bayerische Motoren Werke (BMWA:GR) has an answer: diesel.

It's a fuel that most Americans gave up ages ago. Yet two of every three BMWs sold in Europe are diesel powered. One reason is the high fuel efficiency of diesels. BMW calculates that its European fleet already nearly achieves the U.S. mandate for 2016 of 35.5 miles (57 kilometers) per gallon (3.8 liters).

BMW has now brought diesel to the U.S. It's offering two of its best-selling U.S. models, the 3 Series and the X5 SUV, with diesel engines. The 335d sedan and the X5 xDrive35d are both capable of 550 or more miles on a single tank of fuel.

Audi AG, Daimler AG's Mercedes-Benz (DAI) and Volkswagen (VOW:GR) are also pushing their diesels stateside. My favorite efficient car of 2008 was the VW Jetta TDI, and I'm looking forward to Audi's release of its A3 TDI, which is supposed to get 42 mpg on the highway.

Diesel cars went out of fashion in the U.S. in part because they were rolling pollution factories. The new diesel engines use sophisticated urea-injection and exhaust-scrubbing systems and release 20 percent less carbon dioxide than the typical gasoline engine, while getting as much as 30 percent better fuel efficiency on the highway.

Opting for a diesel is a game of give-and-take. There's a price premium: BMW's $44,725 sedan and $52,025 SUV cost at least $3,600 more than their gasoline-burning counterparts.

It used to be impossible to find a U.S. filling station that would accommodate diesels. Fortunately, you no longer need to search for a truck stop. About 30 percent of U.S. stations now sell the fuel. In terms of performance, you'll sacrifice horsepower and gain loads of extra torque—the hallmark of diesel engines and the reason why heavy tractor-trailers use them.

Both BMW diesels feature the same engine: a 3.0-liter, twin- turbo, in-line six-cylinder. The 335d wins the battle of fun, as it weighs some 1,400 pounds (635 kilograms) less than its big brother. The 335d is the most fuel-efficient BMW ever sold in the U.S. It drinks 23 mpg city and 36 mpg highway, yet still scoots to 60 mph in 6 seconds. That's 10 mpg better than the 3 Series gasoline engine on the open road. In my tests, I got an average of 32 mpg in mixed driving.

While the 335d looks the same as the regular 3 Series, the driving experience is markedly different. The gas version has a 300-horsepower, twin-turbo six, which soars to 7,000 revolutions per minute at redline—the maximum safe speed-and has a clean, endless stream of power. It practically sings arias. Conversely, the diesel is all basso profundo, flush with power at the lower registers and meek above 4,500 rpm. While it has only 265 hp, the massive 425 pound-feet (576 newton-meters) of torque is available at a mere 1,750 rpm.

That means the 335d comes on like a bull when you slap the accelerator, bouncing out of a standstill as if it were a muscle car. And it's content to stay at those lower registers: Even at extralegal highway speeds, you'll rarely see 3,000 rpm on the tachometer.

In comparison, the X5 is a slight disappointment. The thrill of that low-end power is negated by all of the extra weight. It will still make 60 mph in a respectable 6.9 seconds, though the fun factor is much paler. The good news is that once you're up to speed, there's a pleasant sense of sturdiness to the thrum of the engine. The engineers have done a good job of matching the gearing to the X5's ample weight, and the balanced delivery of power feels coherent and thoroughly BMW.

On a recent drive from New York to Connecticut's Lime Rock racetrack, the X5 handled both highway speeds and back roads admirably, even in heavy rain. Part of this is a result of its all-wheel drive, which is standard, but also because of the steady torque on demand.

Best of all, I averaged 23 mpg, which is pretty extraordinary for a vehicle that weighs more than 5,000 pounds.

Ultimately, the best argument may be that I've been able to ignore the fuel pump completely for a range of about 550 miles. Fewer fill-ups in any vehicle is a glorious thing.

Jason H. Harper writes about autos for Bloomberg News in New York. jason@jasonhharper.com

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