With its diesel engine, the 2008 Mercedes-Benz GL320 CDI transports seven people and plenty of cargo while getting mileage worthy of a midsize sedan. The oversize SUV from Mercedes-Benz features all the interior luxury we would expect from the German carmaker, along with performance that favors economy over power. Unfortunately, it uses the same baseline cabin gadgets we saw in its gasoline-engined counterpart, the Mercedes-Benz GL450. This system covers a lot of the basics well enough, but the interface is poor and some features are antiquated.
Test the tech: Wine country road trip
A large SUV sporting the Mercedes-Benz tri-star belongs in California's wine country, where upscale types pretend to rough it as they visit wineries and buy cases of the latest pinot noir or sauvignon blanc. To test out the GL320, we took it on a trip to its natural environment, plotting a course 90 miles north from San Francisco to Lake Sonoma. With the navigation system, we searched the POI database using Lake Sonoma as our search term. It found the recreation area and calculated our route.
The big SUV was unwieldy in the city, but once we got on the freeway it seemed more in its element. Keeping up with traffic and passing slower cars proved easy, as the seven-gear automatic kicked down to lower gears when we floored it, the tach rising up to the 4,000rpm line. Yes, it's a diesel, so redline is at 4,500rpm. Unlike diesels of the past, the GL320 didn't produce excessive noise or a particularly bad odor.
We had an easy cruise in this luxurious box up Highway 101 until the navigation system told us to take the Canyon Road exit, which turned out to be a nice country road through vineyards. A right on Dry Creek Road and we were in serious wine country, with vineyards and wineries at every stop. But we continued on our way to the Lake Sonoma Recreation Area, stopping to enjoy the views and stretch our legs.
When we got back in the GL320, we explored a little farther up a fantastic winding mountain road. But we quickly determined we were in the wrong vehicle for these types of exploits, as the GL320 wasn't making us comfortable in the corners. So we turned around before some sports car out for a spin caught up with us. We followed Dry Creek Road by numerous wineries to Healdsburg, where we reconnected with the highway. The car had been a reasonable cruiser off the beaten path, and we're sure its off-road gear, including an adjustable air suspension, could have handled some rougher terrain, but it wasn't really made for the twisties.
We completed our trip back to San Francisco on Highway 101, doing speeds of around 70 mph. Then back in the city we traversed the tight streets and made it back to headquarters. Assessing our trip, we drove 189 miles and got 23.8 mpg. We didn't need to fill up the tank, as we barely got the fuel gauge needle down by a quarter, but checking the current diesel prices around San Francisco, we noted it would have cost us $3.65 a gallon. Using 7.94 gallons of diesel for our trip, our fuel cost would have been $28.98, a paltry amount compared with what you would pay in its gas-engined counterpart, which gets an average of 15 mpg.
In the cabin
Inside the GL320, you get the usual refinement offered by Mercedes-Benz, with good-looking gauges and switchgear. But the ugly plastic buttons surrounding the navigation screen work against the effect, and we just don't care for the particular shade of tan used through most of the interior. Unlike Mercedes-Benz sedans, which put the seat controls in an easily accessible spot on the door, the GL320 has them on the side of the seat, just like most other carmakers, taking away some of what makes a Mercedes-Benz special.
The GL320 uses the same infotainment interface, with its washed-out blue color scheme and fiddly knob/joystick, as we've seen on previous Benzes. We can only hope that soon the system will be updated with what we saw in the Mercedes-Benz C300. This system controls the navigation and audio functions, both of which are fine, but offer nothing special. The navigation system has perfectly good route guidance and a limited database of POIs. But it lacks advanced features such as text-to-speech, and the map resolution isn't good. We do like that you can enter multiple addresses and get it to compute the best route.