High fuel prices have once again propelled compression-ignition engines into the mainstream, so it's no surprise that automakers, especially the German ones, are bringing more diesel-powered SUVs to America. Mercedes-Benz now offers three such vehicles here: the R-, ML-, and GL320 CDI models. BMW's in-line-six oil burner will appear in the X5 by year's end, and Volkswagen soon will retire the Touareg's V-10 diesel engine in favor of a more modern, efficient, and less expensive 3.0-liter V-6 TDI. Audi, of course, won't be left out. It will use the same diesel V-6 as VW in its Q7 3.0 TDI, which goes on sale in the States early next year.
As you'd expect, torque is the star of the diesel Q7's show. More than 400 lb-ft of torque at a lazy 2000 rpm combines with ultrashort gearing to help launch the Q7 with authority. At first, you'd almost think that the Q7 uses a permanent low-range transfer case, because the six-speed automatic transmission has to click all the way to fourth gear just to accelerate beyond 60 mph. Why does the diesel Audi use such short transmission ratios? Because it's one heavy family hauler. At some 5100 pounds, it's more than 100 pounds heavier than a similarly equipped Q7 with Audi's 4.2-liter gasoline V-8.
The rest of the German-spec Q7 3.0 TDI's driving experience is virtually identical to that of other Q7 models. The interior is gorgeous, although third-row seating is not nearly as spacious as the Mercedes GL's. Body control is impressive, but the price you pay is a brittle ride at low speeds; our test vehicle's twenty-inch wheels only exacerbated that situation. The Q7's diesel engine isn't as smooth or as quiet as the Mercedes diesel, either, and the Q7 is cursed with a poorly calibrated, nonlinear accelerator pedal (as are many other Audis). This isn't helped by a turbocharger that's slow to awake from a dead stop. The good news is that U.S.-bound Q7 TDIs will be fitted with a slightly different turbo, resulting in an estimated power decrease of 20 hp but, according to Audi, a large improvement in off-the-line behavior and no loss of torque.
The U.S. version will also include the addition of urea injection to lessen NOx emissions and help the Q7 TDI meet emissions standards for all fifty states. The Q7 will be able to cover at least 10,000 miles before a refill of the two urea tanks is needed. Refills of the organic liquid will be performed at regular service intervals using a filler next to the fuel cap.
The Q7 3.0 TDI hasn't been rated by the EPA, but Audi claims that the U.S.-spec model should return at least 25 mpg on the highway and travel about 600 miles between fill-ups.
Diesel SUVs such as the Q7 promise more than fuel economy. Their low-revving, high-torque engines are the perfect match for heavy SUVs. With Audi, BMW, and VW joining Mercedes, it looks like reports of the SUV's death have been greatly exaggerated.