The engine is compact and weighs less than 500 pounds. The 5270-pound curb weight of the Q7 TDI is only 100 pounds greater than that of the V-6 gas model, but a lightweight it's not.
Curious about why so many diesels measure an even three liters, we asked Wolfgang Hatz, Audi's head of powertrain development, about this diesel's similar displacement. Hatz offered a response not typical of a German engineer: "Well, there's nothing magic about the displacement. We used to have diesel engines that were 2.5 liters because of various European tax laws regarding displacement. When those laws changed, we expanded our basic engine architecture up to 3.0 liters. This size gives us the power we need for a wide range of vehicles." Indeed, the same engine that powers the Q7 is fitted to a range of European Audis ranging from the A8 down to the A4.
Hatz also foreshadowed upcoming advances in diesel technology. "You know, variable valve timing works on diesel engines," he told us, "so you can expect that we'll see this technology in the future. This engine will get even more efficient."
Efficiency is good, but being green is even better. The 3.0 TDI achieves its Bin 5/LEV II rating thanks to efficient combustion and the AdBlue exhaust treatment system. Similar in concept to how gasoline engines use catalytic converters to reduce harmful NOx emissions, the AdBlue urea solution helps complete the same job for diesel engines, transforming the NOx into harmless nitrogen and water vapor. The amount of the solution used is minimal, about five percent the rate of diesel consumption. The AdBlue tank is refilled during normal vehicle service intervals.
On the road, the 2009 Audi Q7 3.0 TDI drives like a buttoned-down full-size SUV. You'll never mistake it for Audi's R10 TDI Le Mans winner, but acceleration is brisk, with 0 to 60 mph coming in about 8.5 seconds. The six-speed automatic clicked off shifts effortlessly and proved to be a good partner for the diesel. The ample torque made the big Q feel ready to accelerate at any moment.
So the 2009 Q7 3.0 TDI is comfortable and quick, but some people still won't accept the fact that it's a diesel. Even if Audi has made its diesel engine quiet, diesels still smell, right? Not anymore.
On more than one occasion during our participation in the Audi Mileage Marathon, I stood among dozens of idling diesels, and never once did I smell eau d'Diesel. This is not your father's Oldsmobile LT6.