2008 Jeep Grand Cherokee 3.0-liter Diesel Review

2008 Jeep Grand Cherokee 3.0-liter Diesel
More economy and more power make green sense.

By Rex Roy
The Auto Channel
Detroit Bureau

"Don't judge a book by its cover." You know this adage, and sometimes it even means something…like learning the tattooed girl from Starbucks is a Rhodes Scholar. The old saying applies to the 2008 Jeep Grand Cherokee diesel, and here's how: The Grand Cherokee last received a full makeover in 2005.

In industry parlance, this SUV is mid-cycle—another way of saying that its middle aged, old news, not worthy of much attention, and completely out of the media limelight. However, when fitted with the 3.0-liter clean diesel V-6 produced by Mercedes-Benz, the Grand Cherokee suddenly becomes a newly-relevant SUV.

With the exception of a small badge on the rear hatch, you'd never know this Jeep packed a huge diesel punch while sipping fuel like a tree hugging hybrid.

It's not that the tried-and-true Grand Cherokee isn't a fine SUV when powered by any of its three gasoline-fired engines. The Jeep's lightweight unibody and trail rated suspension deliver performance and refinement that compare favorably within the class of five-passenger SUVs.

Certainly, the 420-horsepower SRT-8 models lives in rarified air because of its mind-bending acceleration and cornering performance. However —more like HOWEVER—in 2008 the biggest newsmakers are attracting attention by "out greening" their competition.

Fitted with a modern and efficient diesel made by Chrysler's ex (Daimler-Benz), the Grand Cherokee can now shout "I'm green!" as legitimately as anybody. As judged by the EPA's more realistic testing regimes that were instituted for 2008, the diesel-powered Jeep returns mpg estimates of 17 city and 22 highway for our 4x4 model. This theoretically delivers a cruising range of over 450 miles from its 22-gallon tank, a number we confirmed in our week's test of the vehicle.

This mileage beats every other engine offered in the Grand Cherokee line including the 3.7-liter gasoline V-6. While achieving a 30-percent increase in mileage, the diesel also provides more torque (pulling power) than the GC's optional 5.7-liter Hemi.

The specifications on the diesel are this: 215 horsepower at 3800 rpm, 376 lb-ft of torque at a low1600-2800 rpm, and a towing capacity rated at a maximum of 7,400 lbs. What these numbers don't tell you is that while racking up such impressive performance figures, the diesel produces approximately 30-percent fewer C02 emissions than its gasoline-burning counterparts.

While the above statistics help build a case for driving a diesel-powered Grand Cherokee, old perceptions die hard. The GC's diesel is not a loud, stinking, soot belching beast. The engine is so refined that you'll find this same V-6 under the hoods of Mercedes-Benz E-Class sedans and R-Class crossovers. In fact, the engine is so good that it owns a spot on the respected Ward's list of Ten Best Engines for 2008. http://wardsauto.com/reports/2008/tenbest/winners/daimler_dohc_turbodiesel/

One important reason for its inclusion is driveability. At idle, the engine is smooth. While there is some noise (you can hear the engine running), it's nothing intrusive. Roll down the window, and the timber of the idle sounds a bit different from a gasoline V-6, but you'd never mistake the sound for a UPS truck. But nobody buys a vehicle because of how its engine sounds or doesn't sound (unless it's totally objectionable); people care about how the vehicle drives. And the diesel-powered Grand Cherokee drives very well.

The first thing you notice is its power off the line—it feels unstoppable. The thrust is fluid. The gear changes from the 5-speed automatic are smooth, and once on the highway, the transmission rarely needs to downshift because the engine produces so much torque. The experience is far superior to many V-6 powered SUVs that need to drop down a cog or two just to maintain a set speed when faced with something as minimal as a slight incline.

The Grand Cherokee's 5-speed automatic transmission was a good but not perfect match for the diesel. Cruising upwards of 80 mph had the engine spinning over 3000 rpm (about normal for a V-6), but because of the engine's robust torque, it seems that a sixth gear or a taller overdrive could have increased fuel economy even more. Many of today's SUVs are using 6-speed automatic transmissions, so perhaps an upgrade is in the works, especially since Mercedes-Benz offers the same engine with a 7-speed automatic in their GL320i SUV.

We didn't have an opportunity to drive the diesel off road, but its torque characteristics seem like they would marry perfectly with rock hopping and trail riding. Both activities are low-speed and favor vehicles with abundant torque.

Currently, the Grand Cherokee may be optioned with the diesel in 42 states. Full 50-state certification for this engine is coming in 2009 with the introduction of Bluetech exhaust gas treatment technology. Bluetech is a descriptor used by Mercedes-Benz to identify its cleanest-running diesel engines which will meet or exceed all pending exhaust emissions targets in the US and European markets.

Even without Blutech, the 3.0-liter V-6 is among the cleanest running diesels around. We even gave the tailpipe a sniff while the Grand Cherokee idled in the parking lot of our office, and there was no soot or the awful eau de diesel that one might smell if you tried the same stunt with an older diesel vehicle.

We did notice one curiosity with the diesel; unlike gasoline-powered GCs that include information on instant economy, estimated range, and average fuel economy, our diesel didn't. Our thinking is that the Mercedes-Benz engine electronics aren't compatible with the system existing in the current Grand Cherokees. Perhaps they'll get that sorted out for 2009.

Compared to what hybrids cost, upgrading to this diesel engine is relatively cost effective. Optioning up to the diesel from the base 3.7-liter V-6 runs $3,235. This compares to a similar engine option from the 3.7-liter V-6 to the 4.7-liter V-8 that costs $1,580, but doesn't offer a fuel economy increase or provide nearly the torque of the diesel.

The age of the diesel is dawning on the United States, and because of vehicles like this Grand Cherokee, we should run out and enjoy each new day.

About the author: Rex Roy is a Detroit-based automotive enthusiast, journalist and author. His recently published coffee table book, Motor City Dream Garages, is available at all major book sellers, Amazon.com, and on e-Bay.