Now that Ram has confirmed a diesel light-duty Ram, it’s just in time for us to sample Chrysler’s A630 VM Motori 3.0-liter diesel engine on the Jeep Grand Cherokee media drive. Yes, we know that the Grand Cherokee is not a pickup. However, we think it will give us a good baseline for what to expect when the EcoDiesel is dropped into the Ram.
We expect many systems to be similar in the Grand Cherokee and Ram, including the electrical architecture, the eight-speed automatic transmission and the engine choices. Jeep prices the diesel option at $4,500, and chances are it shouldn’t cost any more when dropped into a Ram.
A Grand Cherokee with the diesel option (the same versions that offer a Hemi) weighs from 5,065 to 5,374 pounds; the gas-engine Grand Cherokee weight ranges from 4,545 to 5,219 pounds. By comparison, the Ram 1500 base (with the V-6) weighs from 4,502 to 5,859 pounds, and the top GVWR of 6,800 pounds is the same as the Jeep 4WD. The maximum gross combined weight rating for the Jeep is 13,100 pounds where the Ram runs from 9,500 to 15,650 pounds, depending on its powertrain and gearing. Rams will use different transfer cases and slightly larger ring-and-pinion sets, and the Ram’s 17-inch tires and wheels are similar to the 18s on a diesel Jeep. The Ram and Jeep should use the same alternators.
Aerodynamics will be the bigger factor in making a comparison. Jeep’s quoted coefficient of drag value is 0.371, higher than the Ram’s 0.360, but we’re guessing a diesel Ram may not get all the high fuel economy tweaks. We don’t think that’s enough to overcome Ram’s larger front, so it makes sense to us that city mileage ratings will be similar but highway ratings will be slightly less than the Grand Cherokee. No doubt a lot will depend on gearings and tire choice.
The VM is a 60-degree under-square 3.0-liter engine with an iron block, aluminum heads, overhead cams and a compression ratio of 15.5:1. It uses a single water-cooled Garrett turbo in the back of the valley, solenoid common-rail Bosch injection (with up to three pilot and two post-injection events per cycle and 29,000 psi) and selective catalytic reduction.
The gas tank has a a capless arrangement that wasn’t quite up to Jeep angles on the prototypes we drove; the tank can hold up to 24.6 gallon fuels, and the urea reservoir is sized to 10,000-mile refill intervals. The oil system has been developed for the steep angles one expects to tackle in a Jeep, and for cold-weather cabin performance Jeep has electric heaters in the air ducts.
Because the temperatures at the event were above freezing, we couldn’t test how long it would take to start the diesel in the cold. For us, at 53 degrees, the wait was no longer than the “ignition on” bulb-check function. The gravelly diesel growl is well muted, with injector tick quieter than some gasoline engine idles — BMW’s 2.0-liter I-4 comes to mind. If you’ve driven any recent 3.0-liter-range six-cylinder diesel, be it VW’s corporate unit, Mercedes’ 72-degree V or BMW’s inline arrangement, the sounds and numbers will be familiar to you.
Throttle response is average. Mash the accelerator from a full stop, and there’s a quiet step-off followed almost immediately by full power, and while it’s certainly not as fast as a Hemi, the diesel engine delivers an effortless midrange-rpm surge that will make passing just an excuse to exercise the turn signals. Jeep didn’t offer a zero-to-60-second time, but the Jeep feels competitive with the Germans, probably getting to 60 mph in the 7.0- to 7.3-second range.
Jeep hits that magic 30 number (EPA highway mpg rating) but only for the 20 percent of Grand Cherokees that are rear-wheel-drive; 4WD delivers 21/28 city/hwy ratings, very similar to comparably weighted competitors: VW Touareg (20/29), Porsche Cayenne (19/29), M-B ML350 Bluetec (20/28) and BMW X5 35d (19/26). Note that Jeep also claims 17/25 (17/24 4WD) with the 3.6-liter V-6 Pentastar and 14/22 (14/20 4WD) for the Hemi backed by an eight-speed automatic. That’s never more than 1 mpg different than the Ram V-6/eight-speed and only 1-2 mpg better than a Ram Hemi with the six-speed automatic.
VM Motori is a 50/50 joint venture between Fiat and General Motors but unless GM is sandbagging a well-concealed diesel program for the new Silverado or Sierra, Ram will be the first half-ton to market in the U.S. with a diesel engine. And if Nissan puts a baby Cummins in a Titan, our test title won’t be a misprint: Ram Diesel Versus Cummins Showdown.