Barry Winfield, Contributor
You'd think that putting a sophisticated turbodiesel engine into a heavy SUV would be a complete no-brainer, right? It looks like the perfect combination on paper. A turbodiesel supplies copious torque at relaxed engine speeds, with much better urban fuel economy and reduced CO2 emissions.
So, what's not to like here with the 2008 Jeep Grand Cherokee Diesel? OK, we need to help the public get over its misconceptions about diesel engines, but that shouldn't be an insurmountable task.
However, what might make it insurmountable is the coincidental increase in the price of diesel fuel, said to be because of the current high demand for the oily stuff in Europe and elsewhere. This has pushed the pump price well beyond the level even for premium gasoline — itself not exactly cheap these days.
As they say, timing is everything, and it seems like diesel technology just cannot get a break in this market.
A Legacy From Mercedes-Benz In the case of this 2008 Jeep Grand Cherokee Limited, the addition of a well-sorted diesel drivetrain from Mercedes-Benz makes a lot of sense. You don't need a peaky, high-revving engine in a relatively ponderous vehicle like an SUV, and this 3.0-liter V6 in common-rail diesel (CRD) configuration feels right at home with its low-rev surge of power and its easygoing redline of 4,500 rpm.
Other than a slightly longer startup crank, this diesel V6 doesn't advertise dramatically different characteristics from its gas equivalent. There's a subtle rumble in the background during normal driving, but it's a pleasant accompaniment soon drowned by tire noise and the rush of the wind.
Abetting the V6 turbodiesel in the quest for seamless propulsion is a very good five-speed automatic, equipped here with a typical manual override system. We're betting that the manual override will only be used for towing and rough-roading, because the trans has virtually telepathic control electronics, and almost always responds as required. In normal city driving, the transmission is a cooperative partner, slurring from one ratio to another as inconspicuously as possible.
But its response in more interesting terrain is noticeably more energetic, and the unit digs quickly for lower gears when needed, then holds onto gears even if you lift when it notices you driving enthusiastically. A typical freeway pass has the box slipping from the overdrive 5th gear into its direct (1:1) 4th gear almost imperceptibly as you press the throttle. The diesel's boost comes up instantly and you sashay past a slower vehicle at an unexpectedly quick rate.
Satisfying Power The other aspect of a turbodiesel that feels satisfying to drivers is good part-throttle torque. Because diesels are effectively unthrottled engines and accelerator application merely fires more fuel into the combustion chambers, they provide an impression of easy power on a light throttle.
There's very little engine braking available from an unthrottled engine, too, and this works to your benefit in moving traffic with the Grand Cherokee diesel, when a lifted throttle allows coasting almost as free as if the Jeep had been left in Neutral.
The peak horsepower produced by this CRD is only 215 hp at 3,500 rpm, and that isn't much for a 4,723-pound, four-wheel-drive behemoth like this Grand Cherokee. But the peak torque is a substantial 376 pound-feet, and it arrives at a leisurely 1,600 rpm. Despite the engine's somewhat reduced range of operation, it almost always feels ready to boogie. The Grand Cherokee gets to 60 mph in 7.8 seconds on the way to a quarter-mile performance of 15.9 seconds at 83.8 mph.
Of course, most of the thrill here is the infrequency with which you visit the refueling station. The CRD version of the Grand Cherokee 4x4 is EPA-rated at 17 mpg city/22 mpg highway, and this seems pretty good compared to a Grand Cherokee equipped with Chrysler's 3.7-liter V6, which delivers 210 hp and 235 lb-ft of torque at the price of 15 mpg city/20 mpg highway. And the diesel is a lot better than the 4.7-liter V8, which has 305 hp and 334 lb-ft of torque and 14 mpg city/19 mpg highway to match. We observed 19.3 mpg during our term with the V6 diesel.
Remember, diesel technology can achieve the same net fuel consumption savings as a hybrid but without the added batteries, computers and mechanicals. A diesel works well in an urban environment and also performs adequately on the open road, where hybrids are just gas-engine vehicles with a bunch of batteries as unwanted ballast.
The Other Stuff The rest of this diesel-powered 2008 Jeep Grand Cherokee Limited is pretty much unchanged. Despite Jeep's refreshed interior design for 2008, we still encounter fairly hard and utilitarian molded surfaces in the passenger cabin, along with the unconvincing faux wood.
The control layout is clean and tidy, and most controls are pretty intuitive. Having adjustable pedal height helps match the driver to the environment, and apart from a sense of sitting fairly high in the vehicle, the driver easily finds a natural relationship to the controls. One obvious ergonomic glitch: The trip meter is selected and controlled by wheel-mounted switches that also access the trip computer functions, and it's all too easy to accidentally reset the meter when all you want to do is scroll on through the menu.
As is typical of many SUVs, interior packaging isn't as generous as the overall vehicle size suggests. Rear-seat space is modest, and the high deck in the rear luggage compartment reduces the overall space back there.
Rated for Luxurious Trails One of the Jeep Grand Cherokee's upsides is a five-link rear suspension and an independent front suspension that provide the wheel travel and control necessary to perform both on- and off-road maneuvers to an acceptable standard. And for a vehicle wearing Jeep's Trail Rated badge, signifying its ability to tackle demanding trails, the JGC doesn't do a bad job of cosseting suburbanites on conventional blacktop.
The compromises made by ride engineers manifest as fairly soft springing, relaxed shock valving and somewhat taut roll control, and this combination works reasonably well in most normal applications. But it's when you try to operate outside the envelope of this compromise that the car's deficiencies emerge. Pitch control is not good enough to prevent severe dive under braking. Hard cornering produces wallowing sensations on imperfect surfaces, and the ride is seldom calm and flat.
And yet the 2008 Grand Cherokee handles surprisingly well. You are always aware of the substantial mass and the limits imposed by the all-terrain tires, but if you're smooth and measured at the controls, the big Jeep traverses twisty roads in a very satisfying way.
Having full-time all-wheel drive helps reduce scrub when you're pressing on by putting the power down at all four corners and letting the tires share the load more equitably. Automatic limited-slip differentials now accompany the Jeep's Quadra-Trac II all-wheel-drive system, and may contribute to the Grand Cherokee's poise, too. On our skid pad, the Grand Cherokee diesel achieved 0.74g, although its slalom speed of 58.2 mph illustrates the consequences of the soft suspension calibration and sizable 4,723 pounds.
A Diesel for Dirt and Travel Even a Jeep Grand Cherokee is expected to be rated for genuine all-terrain travel, and the 2008 Jeep Grand Cherokee Limited CRD finally gets hill-start assist and hill-descent control, features that were noticeably absent in previous years despite their appearance on several rivals.
Those few who need the trail-busting potential in the Grand Cherokee's chassis will surely appreciate the turbodiesel's contribution. You can easily imagine creeping up a steep slope in low-range all-wheel-drive mode with the Mercedes-built oil burner ticking over just above idle with plenty of torque on tap in case you need it.
Diesel really seems to be the right answer in the 2008 Jeep Grand Cherokee. The 19.3 mpg fuel economy we observed is as good as the highway fuel economy of the V6 and V8 powertrains, and we won't mention the 13.4 mpg we've observed in the Jeep Grand Cherokee SRT8. Just as important, the cost surcharge for the diesel engine is just $1,655, a price low enough that fuel savings will pay for it over a reasonable length of time.
But the big question here is the price of low-sulfur diesel, which is higher than premium gasoline. Just as the right diesel technology is introduced to the U.S., the price of high-tech diesel fuel might spoil the moment.
The manufacturer provided Edmunds this vehicle for the purposes of evaluation.
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