2007 Mercedes-Benz E320 Bluetec

Mercedes-Benz has been building diesel automobiles since the 260D of the 1930s, so it's no surprise that Mercedes is the first and only manufacturer to make a diesel passenger car that meets newly tightened U.S. emissions regulations for 2007. With its new V-6 turbo-diesel, the E320 drops the CDI suffix in favor of Bluetec. Bluetec refers to AdBlue, the nice name Mercedes gives to the urea-based liquid additive that helps the Bluetec diesel achieve ultralow emissions. For the '07 model year, however, the new Bluetec diesel V-6 doesn't yet use urea injection; it therefore cannot meet emissions standards in California (and the other states that use the same, stricter standards). Mercedes hopes to debut the urea-injected Bluetec diesel next year, in the GL-class, the R-class, and the ML-class, which would all be fifty-state compliant.

While today's new Bluetec Benz can't meet California standards, it is significantly cleaner than the outgoing straight-six diesel, an achievement made possible largely by the arrival of ultralow-sulfur diesel fuel (which, by federal mandate, has been at 80 percent of diesel retailers since October 2006). Although the E320 Bluetec's 208 hp and 400 lb-ft of torque would seem to be a significant improvement over the E320 CDI's 201 hp and 369 lb-ft, by factory estimates the new car needs the same--still quick--6.6 seconds to accelerate from 0 to 60 mph; and the Bluetec's fuel economy actually slips slightly, by 1 city mpg, to 26/37 mpg.

But there's more to the story than lower emissions and similar performance. The new turbo-diesel V-6 is the smoothest and most well-mannered diesel to date. This oil-burner's sound is more murmur than clatter, and even then it's discernible only at low speeds. With more torque than an E550, it will rocket away from a stop with tire-chirping urge, and the turbocharger is seamlessly integrated. The 0-to-60-mph figure is essentially the same as an E350's, yet the fuel economy is better by 7 mpg city and 11 mpg highway, and its range can top 700 miles on the highway. For all that, the E320 Bluetec costs only $1000 more than the gasoline-powered V-6 E-class.

Cleaner, quieter, smoother, but still economical and plenty quick, the E320 Bluetec is one polished diesel. Unfortunately for advocates of diesel passenger cars, for this year at least, it's a party of one.