The Good: The 2007 Mercedes-Benz ML320 CDI gets decent mileage compared to other luxury SUVs, and the engine gives it solid acceleration. Air suspension and all-wheel drive give it off-road capability. We also like the voice-command interface and the navigation system's route guidance. The Bad: The COMAND interface uses a fiddly joystick that's difficult to use. The MP3 CD player doesn't show ID3 tag information. Its options are very pricey, and it doesn't meet the emissions requirements for California or New York; therefore, it's not available in those and three other states. The Bottom Line: The 2007 Mercedes-Benz ML320 CDI is a very drivable car, but you'll pay dearly to option it up with cabin electronics, should you live in a state where you can buy it. We're impressed by the off-road equipment, but who would really take this car into the mud? Photo gallery:2007 Mercedes-Benz ML320 CDIWe associate Mercedes-Benz with big, luxury cars, but the 2007 Mercedes-Benz ML320 CDI breaks through that image with its diesel engine and serious off-road gear. We don't know who would thrash a $60,000 car over boulder-strewn rutted dirt roads, but Mercedes-Benz insists the car can handle it. As for its diesel engine, Mercedes-Benz does a good job of keeping it a secret. The engine runs quietly and smoothly, with only a hint of the usual clatter you hear from diesels, and we didn't notice any soot or smell. Some of this inoffensive behavior can be attributed to the new ultralow sulfur diesel fuel (ULSD), which significantly lowers emissions. ULSD was phased in over the last few years, and now, any time you find a pump selling diesel fuel for passenger cars, it should be ULSD. In the ML320 CDI, diesel power means very high torque along with better fuel economy than its gasoline counterpart. Our ML320 CDI test car was in form a typical small SUV, with two rows of seating and a cargo area. But this is a Mercedes-Benz, so the level of luxury was way above that of a Mitsubishi Outlander or a Honda CR-V. The front of the ML320 isn't much higher than a sedan's hood, making for a pronounced slope down from the windshield, and contributing to a bulbous look for the front of the cabin. But we like how the rear side windows, behind the C pillar, seem to wrap around the rear of the car. Our ML320 had a few extras including metal running boards and skid plates, all part of the Sport package. Test the tech: Diesel quest While examining our newly arrived ML320, we noticed the warning notice on the fuel door and the bright red fuel cap, telling us to use only low sulfur diesel fuel. We knew that, by law, any diesel fuel sold for passenger cars had to be ULSD, but we couldn't recall having seen many diesel pumps lately. For our tech test with the ML320, we wanted to see how easily we could find fuel. We started out at a random location down the peninsula from San Francisco, in Menlo Park on El Camino Real. This seemed like a good place to start, as the navigation screen showed a bunch of gas station icons in our immediate vicinity. With the first couple just a half mile down the street, we arrived quickly to see a Chevron and a Union 76 on opposite blocks. But we found no diesel pumps at either. There's no diesel at this pump.Continuing down El Camino Real, we found a Shell station but were out of luck there, too. So we veered off the main drag toward a small cluster of gas stations on our navigation screen. We quickly found a Quick Stop and another Shell, but still no diesel. It was getting frustrating, but we continued on to another row of gas station icons along Highway 84. There were more Chevrons and Shells, but still no diesel. Then, on the opposite side of the road, we saw a seedy-looking little market plus gas station called the Gas and Shop. Among their signs was an advertisement for Diesel No. 2, along with a per-gallon price close to that of premium gas. But we were successful, though we hope California has been vigilant about making sure only ULSD is sold for cars, as we wouldn't want to destroy our nice, new Mercedes-Benz. All in all, we tried eight gas stations before we found one that sold diesel. Because we were in an urban area, we had to travel only seven miles to find our diesel. In the cabin The cabin of the ML320 CDI has all the luxury we would expect from a Mercedes-Benz, even if it is meant to handle wild and wooly off-roading. Of course, the seats are power-adjustable, and the windows require just one touch of the switch to go all the way up or down. And there is a bit of wood trim on the ML320, covering the lower half of the stack and leading down to the console. This COMAND interface is used on Mercedes-Benz's less expensive cars, and it's a pain to use.But the controls sitting around the LCD at the top of the stack use the low-rent version of Mercedes-Benz's COMAND interface. Rather than the big metal knob on the upscale COMAND system, this one gets a fiddly, little plastic joystick, with buttons along the bezel of the LCD. The joystick suffers from the problem that, when you push it in to enter a command, it often slides to the side, changing your selection. A touch screen would have been preferable. On the software side, it's not immediately clear how to select menu items because of the faded color scheme, but it's easy to use once you understand it. On the plus side, the ML320 incorporates an excellent optional voice-command system. We were able to set destinations in the navigation system, choose tracks from a CD or satellite radio stations, and control other functions in the car. The LCD offers good feedback, letting you see what commands you've just made and which ones are available. The voice-command system also has some flexibility, for example, accepting either "navi" or "navigation" as commands to enter the navigation system functions. The maps have great onscreen resolution, but the system is a little frugal about displaying street names. As we drove along, it failed to show the names of most cross streets, making navigating by map problematic. But we really like its route guidance, which has rich graphics for upcoming turns, gives plenty of warning, and is very good about showing the car's precise location. As for destination entry, it's about average. It can take you to a freeway entrance, an address, or a point of interest. But its points-of-interest database isn't comprehensive. As the ML320 claims off-road prowess, the navigation system also has an off-road mode and a compass screen, which shows GPS coordinates and elevation. One CD slot lives behind the screen, while an optional changer lives in the glove box.A button labeled Eject, at the bottom of the LCD, causes the screen to motor open, revealing a CD slot. We also had an optional six-CD changer mounted in the glove box. Both CD players can read MP3 tracks, but the stereo interface doesn't show ID3 tagging information. Still, we found it easy to choose folders and play music. Satellite radio is also available, and there is an auxiliary input mounted in the glove box. The Harman Kardon Logic7 audio system pushes 440 watts through 11 speakers and a subwoofer, delivering excellent clarity. We could hear things on our CDs that we couldn't hear on other systems, which wasn't always good. Occasionally we could hear imperfections that made it through from the original recording session. While we liked the system's clarity, it didn't have much punch, even when we tried to maximize bass and treble. This system sounds incredible with acoustic guitar and classical music, but it doesn't make rock music stand out. We didn't have a Bluetooth cell phone system on our car, but it is available. Mercedes-Benz resisted Bluetooth for awhile, but the company seems to have accepted it now, quietly making it an option along with the old cradle system. Under the hood After our first few days driving the ML320, we noticed the fuel gauge had gone down by only about a third. At first we attributed the fuel level to excellent diesel fuel economy, but we found we had been getting about 21 mpg, not bad for a Mercedes, but pretty similar to what we got with the gasoline-powered Mitsubishi Outlander. A quick look at the specifications showed that the ML320 comes with a 25.1-gallon fuel tank, which gives it incredible range and suggests you'll want to top it off whenever you find diesel at a good price. This turbo-charged diesel engine puts out 398 lb-ft of torque in an rpm range from 1,400 to 2,800.Under its new testing, the EPA gives the ML320 19 mpg in the city and 24 mpg on the highway. Our overall observed mileage comported with those numbers, coming in at 21.6 mpg. The ML320 isn't available in California, Maine, Massachusetts, New York, or Vermont due to its emissions, so it hasn't been rated by the California Air Resources Board. It also hasn't been given a Federal emissions rating, but its greenhouse gas emissions, at 10.1 tons per year, aren't particularly good. Mercedes-Benz doesn't approve the use of biodiesel in the ML320, due to fears it will clog the injectors. The experience of driving a diesel is unique. The turbo-charged 3-liter V6 puts out 215 horsepower at 3,800rpm, and 398 lb-ft of torque from 1,400 to 2,800rpm. That huge torque number makes the ML320 leap forward readily, overcoming any potential turbo lag. With a redline of 4,500rpm, you won't be taking it too far beyond its peak torque range, either. Mercedes-Benz supplies it with a seven-speed automatic transmission, so in most circumstances, it will stay at peak torque. In our driving, we found the steering very responsive, but you can't really thrash it around corners because of its high center of gravity. The ML320 compensates a bit with its air suspension. In automatic mode, the car lowers itself at high speeds. Or you can take charge by putting it in Sport mode, which keeps it lowered but provides a rigid ride. Comfort mode raises it and does a good job of absorbing the potholes. The DSR button controls the downhill speed in the ML320, while the suspension controls raise and lower the car.For off road, the ML320 has descent control, an off-road mode, and Mercedes-Benz's 4matic full-time all-wheel-drive. You can set the speed for descent control, which defaults to 6 mph. Off-road mode maximizes torque--the manual says it should be used off-road or for towing things up hill. 4matic delivers a 50-50 torque split between the front and rear wheels. In sum The 2007 Mercedes-Benz ML320 CDI 4matic has a base price of $43,680, but as we mentioned above, you can't buy it in California, Maine, Massachusetts, New York, or Vermont. Our test car came loaded with park distance control ($760), voice command ($500), the six-CD changer ($440), the Premium III package ($8,600), leather seats ($1,520), the Lighting package ($900), the Sport package ($1,550), and a paint color called Alpine Rain ($700). Along with the $775 destination charge, the whole thing rolls in at $59,425. The Premium package is the most costly out of these options, but it includes the Harman Kardon stereo and the navigation system, among other niceties. We generally found the ML320 an enjoyable and capable car to drive. Mercedes-Benz makes its diesel power train mostly transparent, as the cabin is well-insulated from the clattering engine. We find the off-road gear a little mysterious, as we can't imagine anyone wanting to scratch the paint. If you're looking for a luxury off-roader, the Land Rover LR3 is very capable, costs about the same, and has similar tech. For a more road-oriented luxury SUV, the Infiniti FX45 can be well-equipped for a little less money than the ML320. But none of these competitors has a diesel power plant, so the ML320 gets the edge in mileage by about 4 mpg. Of course, that counts only if you live in a state where you can buy it.