Audi Diesels Top Expectations in Cross-Country Marathon

October 14, 2008
Audi Mileage Marathon

Audi Mileage Marathon

Last week brought you an update from Audi’s Mileage Marathon, a 4,800-mile tour with a fleet of clean-diesel TDI diesel vehicles.

On the first day alone, a Q7 achieved 31.8 mpg on the New York-to-Washington leg--including battling Manhattan stop-and-go traffice. For the same stretch, an A3 2.0 TDI returned 47 mpg, an A4 3.0 TDI eked 39 mpg, and the new Q5 3.0 TDI--which the U.S. market won’t see for some time--turned out a surprisingly high 38 mpg.

I joined only for the first 1,000 miles or so, from New York to Washington, D.C., and on to Chicago, with most of the distance covered in the new Q7 3.0 TDI, the model that early next year will mark the return of the diesel for Audi in the United States and the first TDI with the automaker’s new ultra-low-emission system. My co-driver and I managed an also very respectable 30.9 mpg that first day, being extremely mindful to keep our speed below 65 mph and to maximize our coasting. No A/C either, though we happily didn’t need it that day.

For the rest of the trip, we decided to drive just like 90 percent of everyone else on the road--maintaining the speed limit, or even a little higher, running the climate control freely, and avoiding jack-rabbit starts but not "hypermiling" (taking momentum conservation to an often-unsafe max). The penalty? Not much at all--we still averaged about 29 mpg for the rest of the trip.

And that's the goal of the Marathon: to prove that Audi's TDI's engines return impressive fuel efficiency in real-world driving conditions, without reducing comfort or resorting to hypermiling techniques.

As we reported earlier in the year, the Q7 TDI employs a new urea-injection system that sprays a solution called AdBlue into hot exhaust gases to reduce NOx emissions. Although the filler neck for the AdBlue reservoir is located conveniently next to the diesel filler neck, AdBlue only needs to be refilled at the Q7’s regular service intervals, and the vehicle meets 50-state U.S. emissions and Europe's proposed tougher Euro6 standards for 2014.

The 3.0-liter direct-injection diesel V-6 in the Q7 TDI makes a respectable 221 horsepower, but it's the 406 pound-feet of torque, available at a low 1,750 rpm, that makes TDI version feel every bit as strong as the 4.2-liter V-8 version--which returns fuel economy in the teens in most types of driving. Hook up a boat trailer in back, and we’d venture to say that the TDI is the best choice.

But as a reality check, nearly 30 mpg isn’t spectacular for a Mileage Marathon. While it’s considerably better than other 5,000-pound sport-utility vehicles, the V-6 gasoline versions of almost any mid-size V-6 sport wagon, with careful driving, will return about the same mileage.

Enter the A3 2.0 TDI, which is powered by the same four-cylinder turbodiesel that’s now going on sale in the new Jetta TDI. The Jetta TDI is rated at up to 41 mpg highway, but that seems to undercut the engine’s real-world fuel efficiency.

In a stint from Toledo to Chicago, I drove the A3 TDI and achieved nearly 47 mpg over the course of a day, including a mix of fast 65 to 75 mph cruising and some slowed-down driving in commuter congestion. I love the nimble nature of the A3 with the 200-horsepower, 2.0-liter direct-injection gasoline four-cylinder, but I’ve found a new favorite that happens to feel even faster while remaining as frisky and nimble.

That’s what America needs, and Audi of America chief Johan de Nysschen hinted that we might just get it.

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