Mercedes has made it official: Diesel power will be offered in its 2007 SUVs, giving the Stuttgart three-pointed star bragging rights for the first diesel seven-seat 'ute on the market following the cancellation of the Excursion.This is just one aspect of Mercedes' approach to consumption reduction, as its hybrids, fuel cells, and direct-gasoline-injection vehicles continue to evolve. The company doesn't see diesel as the only answer, but with fuel savings of 25 to 40 percent and minimal to no loss in performance, it's a viable option.
The 320 CDI badge will find its way onto the ML- and R-Class this fall and the GL by early 2007, starting with 45-state sales and eventually expanding to 50-state applications. As it did with its 450 and AMG 55 and 63 labels, Mercedes took some license; the 320 CDI is a 3.0-liter and the Euro-only (for now) 420 CDI is a 4.0-liter.
Undersquare dimensions (bore is less than stroke) are typical in diesels and are 3.27 x 3.62 inches for this all-aluminum V-6. However, the V angle is 72 degrees, crank pins are offset, and a balance shaft was fitted, all to ensure smoothness. Dual chain-driven camshafts impel four valves per cylinder around central piezo injectors, with maximum injection pressure of 23,500 psi, an amount that would quickly erode the top of a traditional-material piston; all we could find out about the piston content was that it's "proprietary."
The injection system is the most modern version of common-rail and runs five events per cycle, two pre, one main, and two post injections, through eight-hole injectors. The variable-nozzle turbocharger generates close to 29-psi maximum boost pressure.
As fitted to the 'utes, the OM 642 engine will be rated 224 horsepower at 3800 rpm and 376 pound-feet of torque from 1600 to 2800 rpm. It starts making usable boost at 1400 rpm and is on full steam shortly thereafter, falling off from 2800 rpm. However, there's more than 200 horsepower available from 2800 to 4200 and still 260 pound-feet on tap as fuel flow cuts back approaching the governed no-load engine speed at around 4600 rpm. It'll be teamed exclusively with the 7G-Tronic seven-speed automatic.