You know what some journalists do when we get behind the wheel of a test vehicle... we hammer the throttle, shift at redline, late-apex every corner, and hope the manufacturer doesn't measure tire-tread depth after the car is returned. Different behavior wouldn't be in-line with The Official Journalist Creed.
Well, the creed is more a set of guidelines than rules, so our responsible behavior whilst participating in the Audi Mileage Marathon can be excused. During our three full days behind the wheel of a 2009 Audi Q7 fitted with the 3.0-liter turbo-diesel, we were easy on the throttle, coasted a lot, and worked to maximize fuel economy, not speed. The results were impressive, as we achieved almost 31 mpg during one jaunt from Mammoth Lake to Monterey, California. Furthermore, when we drove with complete disregard for efficiency, we still couldn't push our average mileage below 26 mpg. This kind of fuel economy matches that of many smaller sedans and is similar to what we observed when driving the 2009 Chevrolet Malibu Hybrid.
What makes the new Q7 TDI's mileage remarkable is that it comes from a full-size, luxurious SUV that seats seven, tips the scales at more than 2.5 tons, and has fourteen cupholders. This isn't your typical eco-weenie penalty box on wheels - it's a leather-lined and fully equipped vehicle with just about every feature you could want. Voice-activated navigation, Bluetooth, and an iPod adapter, for instance, are available and were fitted to our test car.
These features, however, don't separate the 2009 Q7 from any other highline SUV; Audi's fifty-state legal 3.0-liter TDI V-6 does. The turbocharged (T) diesel with direct injection (DI) joins two gasoline engines in the Q7 lineup: a 3.5-liter V-6 and a 4.2-liter V-8. The diesel highlights Audi's approach to improving fuel economy and emissions, and the engine recently earned the stringent fifty-state Bin 5/LEV II certification.
The 3.0-liter turbo-diesel produces 221 hp and 406 lb-ft torque. The single, variable-geometry turbo resides in the valley of the cylinder vee. Maximum boost is a staggering (by gasoline engine standards) 37.7 psi. Cylinder heads made from a high-strength vermicular graphite iron weigh fifteen percent less than traditional cast iron and utilize four valves per cylinder. Fuel is delivered through a pressurized common rail to piezo injectors at 29,000 psi.
With this kind of pressure, the injectors optimally provide fuel over the entire power stroke to maximize efficiency and minimize noise. The traditional semitruck-like diesel sound comes from the fuel charge igniting all at once. The 3.0-liter TDI delivers and burns each fuel charge over a brief span of time, thereby reducing engine noise.
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.
Audi uses Quickstart heater plugs to solve another historic diesel problem: long prestart regimes in cold weather. The V-6 will fire within two seconds even when the mercury is frozen at the bottom of the thermometer bulb.
Perhaps the best part of living with Audi's oil-burning Q7 is its fuel range. Our experience and Audi's estimates indicate that 600 miles per tank should be easy to achieve on the highway, so you'll want to be sure to hit the restroom before you leave. With that kind of fuel range and standard Quattro, not much is going to slow you down.
The Q7 3.0 TDI goes on sale in January of 2009. Prices and mileage estimates are forthcoming.