Jeep Cherokee/Grand Cherokee diesel

No longer are diesels just for farmers, commercial vehicle operators or hard-core off-roaders preferring low-down grunt over on-road refinement. Car makers, and four-wheel drive marques in particular, are spending up big on diesel technology and starting to convince everyday drivers of the merits of clean, efficient, diesel power. In Europe, diesel commands a bigger slice of the passenger car market than petrol - companies like Peugeot and Renault sell two thirds of their vehicles with oil burners up front.

Chrysler's 60-year-old Jeep brand is the latest to jump on the new-age diesel bandwagon, adding a state-of-the-art diesel engines to its mid-sized Cherokee and luxury Grand Cherokee off-roader line-up.

The Cherokee's new common-rail direct injection engine is basically a larger, more powerful 2.8-litre version of the 2.5-litre diesel already available with the Cherokee. The Grand Cherokee, despite its all-American heritage, gains a direct-injection diesel and matching five-speed automatic transmission from Mercedes-Benz - one of the benefits of the Daimler-Chrysler tie-up.

The Mercedes oil burner utilises the latest common-rail direct injection (CRD) technology and full electronic control already proven in the Sprinter van and M-Class wagon.

Whereas traditional diesel engines use a mechanical pump to fire fuel to individual injectors, the CRD engine uses a high-pressure pump to deliver the produce via a single fuel rail.

The result, according to Chrysler Jeep, is better performance, lower fuel consumption, reduced emissions, and improved driveability. And after testing the 2.7-litre CRD Grand Cherokee over a variety of terrain in NSW's southern highlands, we tend to agree.

On a number of measures, the new diesel Jeep stacks up well against the existing six-cylinder and V8 petrol engines in the Grand Cherokee range. For starters, the more efficient fuel delivery system of the CRD engine seems to have eliminated most of the noisy clatter caused by more traditional oil burners. Although there's some clatter at start-up, once out on the road it's as refined as a petrol V8.

Poor acceleration is another common complaint with diesel engines, and this has been addressed by a so-called Variable Geometry Turbo. The VGT system produces more air from the turbo at low revs, which overcomes the dreaded 'turbo lag' often associated with turbo-diesels.

For acceleration, the 2.7-litre diesel is only slightly off the pace compared to the Grand Cherokee's standard 4.7-litre petrol V8 - 11.2sec for the 0-100km/h - and mostly makes light work of lugging its hefty 1925kg body around.

The Grand Cherokee's V8 produces more power, but the diesel offers more impressive torque figures. Both produce a similar peak of around 400Nm, but the diesel achieves this at much lower revs - between 1800-2600rpm - which makes it a better proposition for off-road driving and towing.

In fact, the diesel has the best towing capacity (3360kg) in the Grand Cherokee line-up, which is good news for those wanting to pull a big boat, caravan or horse float.

The 2.7-litre diesel will also save you money at the fuel pump. Figure on an average consumption of 9.7lt/100km, compared to a relatively thirsty 15.8lt/100km from the big petrol V8.

When it comes to handing over your hard-earned, the diesel also comes up trumps. At $69,890, the 2.7-litre Grand Cherokee Limited is $100 more than its V8 equivalent. While the new 2.8-litre diesel-powered Cherokee Limited, for example, at $53,990 is only $3000 more than the 3.7-litre V6 model.

Other claimed benefits of the new diesel, such as increased service intervals and less need for maintenance, also give it an edge over the petrol variants. The Grand Cherokee's reputation as a comfortable five-seater wagon and competent off-roader is further enhanced by the new Mercedes engine and smooth five-speed auto.

The diesel's low-down pulling power came to the fore during more challenging off-road sections. With a good spread of torque early on, and low-range gearing, the diesel Grand Cherokee takes steep, slippery inclines in its stride. Good height clearance combined with a plush ride also allows it to sweep along rutted fire trails with ease.

The Grand Cherokee also copes well with steep declines, despite the lack of any electronic descent aids common on many of its rivals. Again, low-range combined with controlled engine braking allows for a safe crawl down sharper drops.

The new drivetrain is not the only addition to the Grand Cherokee range. Jeep has made improvements to on-road feel, adding lighter pressure shock absorbers for a better ride, a lighter brake pedal feel and new brake calipers for improved braking, and reduced the steering effort.

Front and rear-side curtain airbags, as well as front airbags, are now standard, as are rain sensing front wipers.

The Grand Cherokee and Cherokee get an impressive kick from the latest direct injection diesel engines - to the point where many buyers could end up overlooking the petrol alternatives next time they visit a Jeep showroom.