I paid tribute to the memory of inventor Rudolf Diesel, born 150 years ago, as well as to the Bay Area's green freak flag as I tooled around San Francisco in a Mercedes-Benz ML320 BlueTec, which has a newly cleaned up diesel engine. After a few states (starting with California) banned the sale of light-duty diesel vehicles because of their emissions, Mercedes put AdBlue, a solution that zaps emissions, in its diesel models. When fueled with ultra-low-sulfur diesel, the ML320 BlueTec is clean as a whistle -- or at least a lot cleaner than the smelly rattlers of diesels gone by.

The SUV's V-6 engine isn't a burner in any sense of the word, but the seven-speed automatic transmission was lively and had ample power. The four-wheel-drive SUV handled the nearly vertical streets of San Francisco with aplomb. I frequently found use for its downhill speed regulator, a type of cruise control that limits your velocity on steep declines, which helped calm my queasy stomach on Lombard Street. The roomy interior, with an optional Harman/Kardon surround-sound stereo and power sunroof, even kept things comfortable on the way to a 49ers game. The back easily held a full-size grill, a large cooler, chairs, and numerous bags filled with meat and cheese without requiring the three healthy dudes in the second-row seats to give up their 40 inches of legroom. And the power liftgate made unloading the back a little easier.

Mercedes-Benz ML320 BlueTec

Sticker Price
$49,475; $62,100 as tested

Vital Stats
210-hp 3-liter V-6 turbo diesel engine; 398 pound-feet of torque; 18/24 mpg

Good Stuff
The GPS handily points out the gas stations that carry diesel. Plus, the gas mileage is pretty good, and the tank holds 25 gallons, so you can go more than 500 miles on a fill-up.

The suspension is a bit bouncy, and you have to get the AdBlue tank filled about every 10,000 miles at a dealership. If the tank runs dry, the engine will start only 20 more times until you refill it.

Second Opinion
"The ML320 BlueTec is clean, efficient, and quiet," says Gary Vasilash, editor in chief of Automotive Design & Production. "Worries that the engine will announce your arrival as if you were pulling up in a big rig should be allayed."