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Transmission: Seven-speed automatic
Drive: All-wheel-drive
Fuel economy (litres/100 km): 11.6 city/8.5 highway; diesel fuel
Alternatives: Lincoln Navigator, GMC Yukon Denali, Audi Q7, BMW X5, Cadillac Escalade, Chrysler Aspen, Lexus GX470, Infiniti
QX56, Land Rover LR3

There is a reason why those big 18-wheel rigs are powered by diesel engines and it is the same reason why Mercedes-Benz's big GL 320
CDI ($69,500) is what you need if you are looking for an SUV with three rows of seats to tow your boat and handle a long vacation drive with family or friends or both. If you can afford it, that is.

As a commuter car, well, the seven-passenger, 2,430-kg GL leaves something to be desired; it is just so big (5,088 mm in length) and
therefore completely unsuitable for parking in a downtown underground garage. SUVs in general are, in fact, not a particularly great good
choice for rush-hour traffic, though a surprisingly large number can be found doing the 401 shuffle.

Apparently for some the image thing really matters. For others, well, they might be the pilot of a car pooling club, though in my
experience that's rarer than a winter tan in Iceland.

But if you must commute in an SUV, you could do worse than the GL diesel here. The GL 320 CDI is a very good example of what auto
makers are doing with their SUVs, trucks and other large vehicles that use a lot of fuel.

In this case, the story begins with the diesel engine, of course. In the case of the cleaner-burning CDI (215 horsepower and a whopping
398 lb-ft of torque at a low 1,600 rpm) the fuel economy is about the same as a mid-size sedan: 11.6 litres/100 km city and 8.5 highway
from the 3.0-litre V-6 diesel engine.

As a whole, auto makers are using a variety of technologies to improve SUV fuel economy. With little diesel technology of its own,
Toyota, for instance, has focused on gasoline-electric hybrids. The Highlander is now entering its second-generation as a full hybrid.
General Motors, meanwhile, will have a diesel version of its large SUVs within two years and coming in months are SUVs with a new
dual-mode hybrid system. Even sports-car builder Porsche recently showcased a hybrid version of its speedy Cayenne SUV, planned for
sale by 2010, at the recent Frankfurt motor show.

And all auto makers are working on developing special lightweight parts and systems to cut down fuel consumption. For instance,
manufacturers are working on weight-saving electronics to replace mechanical systems and light materials such as aluminum, carbon fibre
and plastics are reducing fuel-robbing bulk.

Alas, good as it is, the GL 320 CDI is not a showcase for those coming advances. On the other hand, its diesel power is impressive, as is
the fuel economy.

Although the 320's six-cylinder diesel generates less horsepower than the eight-cylinder gasoline engine in the 335-hp GL 450 ($76,500), it
produces more torque — the energy that gets the vehicle moving quickly from a standstill and gives it a peppier feel at low speeds. The gas
GL is also thirstier: 16.3 L/100 km city/11.7 highway, using premium gas.
You might have noticed the base diesel model is a lot cheaper than the gas, too. The gas version is better equipped, true, but the diesel
engine is a better choice.

Just so you know, Mercedes also added a diesel version of its ML-class medium-size SUV (five-passenger). If you don't need room for
seven, the ML 320 CDI is an excellent luxury workhorse and at $59,800 is $10,000 less than the GL diesel. Jeep also began selling a
Mercedes-sourced diesel version of its Grand Cherokee in May, starting at about $10,000 less than the diesel ML.

More diesels like them, as well as more diesel passenger cars, are coming. Diesels certainly are poised to become more popular with
drivers looking for fuel-efficient options. They are absolutely brilliant for towing, as my recent test of a GL 320 CDI proved.
With a maximum tow rating of 3,402 kg, it easily managed a decent-sized water ski boat up and through some very hilly terrain. All with a
one-tank fuel range of about 1,000 kilometres.

The 320 has Mercedes' Bluetec technology, which allows it to meet fairly tough emissions targets. Next year, Bluetec will get even
cleaner, too, as the technology improves. Hybrids are still cleaner than the cleanest diesels, by far, but the Bluetec is still pretty good on the
emissions front
It is pretty refined in other ways, too. The GL 320 is not one of those clattery diesels of the past, though it is not dead quiet. With the
windows up, the diesel engine is barely audible; but roll them down and the fairly large V-6 engine sounds more like it belongs in a
delivery truck than a luxury SUV.
It's not a terrible racket, just very different from a gasoline V-6. On the other hand, the big and torquey engine pulls and pulls away like a
truck. Power off the line — after dipping deep into the long-travel gas pedal — is almost neck snapping.
On the highway, the truck-like sounds fade away. Turning at only 2,100 revolutions per minute at 110 km/h, the engine makes just a
distant hum. The big torque means passing is easy, and while there are buttons behind the steering wheel that allow the driver to manually
shift the gears of the seven-speed automatic transmission, they aren't really necessary.
My test model was loaded with thousands of dollars worth of extras that made life easier and ultimately more expensive. Premium leather seating ($2,500) and voice control for the navigation and audio system ($650) are nice but not necessary.
For a big rig, the GL is more nimble around town than you'd expect. On the highway, it is simply effortless and luxurious.
The seating is tall and comfortable, visibility is good and the GL comes with more safety features than you can count. The whole package
is well done.
This is a good thing because if you buy one, expect that diesel engine to last. It would not be surprising to get 300,000 km out of the engine
in a 320 CDI, perhaps more.
Combine the 320 diesel's above-average fuel economy with a comfortable ride, excellent towing and overall drivability and there is an
economic case to be made for this big luxury SUV. If you can afford the sticker price, of course.