2009 Mercedes-Benz ML320 BlueTEC

Dawning of a new day for diesels

Mac Demere / autoMedia.com

The 2009 Mercedes-Benz ML320 BlueTEC will make you forget everything you thought you knew about diesels. It’s quiet, quick, clean and odorless.

Clean and Quiet Diesel

Inside, the ML320 is as silent as you would expect of any Mercedes. Listen closely from the outside and you can hear a hint of the old diesel clatter, but it’s far from attention attracting. With nearly 400 pound-feet of torque as low as 1,600 rpm, the 2009 ML320 diesel accelerates from a rest to 60 mph in about 8.0 seconds: That’s quicker than many sporty cars, and more than adequate to allow easy merging onto a busy freeway from a stop at a metered on-ramp. None of the familiar diesel soot or stink comes from the tailpipe. Mercedes says it is “the world’s cleanest diesel.”

What makes this possible is ultra-low-sulfur diesel (ULSD), which has less than 15 parts per million of sulfur. ULSD burns cleaner and allows the use of catalytic converters and filters. The exhaust of the Alabama-built ML320 travels first through an oxidation catalyst, which removes leftover hydrocarbons. Then a particle filter traps soot before a second catalyst, a chemical, called AdBlue, is sprayed into the exhaust. This combines with smog- and acid-rain-causing nitrogen oxide (NOx) to create harmless nitrogen and water vapor.

ULSD has flowed from many pumps since 2006 and, by the end of 2010, will be the only highway diesel available. Unlike diesel fuel of yore, ULSD has less odor than gasoline. (The areas around pumps that previously dispensed old-style diesel retain some of the stink.) Mercedes says the ML320 will go more than 600 miles on a tank of fuel. The previous generation of diesel fuel, which had 500 ppm sulfur, was called Low Sulfur Diesel and had the unfortunate acronym LSD. If a driver confuses LSD for USLD or can’t find USLD, a single tank full won’t permanently ruin the system.

Turbocharged Performance

ML320’s engine is a turbocharged, double-overhead cam, four-valves-per-cylinder 3.0-liter V-6. It peaks at about 215 horsepower but makes nearly 400 pound-feet of torque from 1,600 to 2,400 rpm. This helps give the ML320 CDI a towing capacity of up to almost 8,000 pounds.

The engine is coupled to a seven-speed automatic transmission. The 4Matic all-wheel-drive system splits power between the front and rear axles. For those few who take the five-seat ML320 further off the highway than an unpaved soccer-field parking lot, Mercedes-Benz has simplified the off-road programming. A push of a single button recalibrates all systems—traction control, anti-lock brakes and more—for off-highway driving. Like all MLs, the 320 employs an electronic traction system that uses individual brakes as a substitute for conventional limited slip and locking differentials.