The TDI's 225 hp is less than the current 3.6L VR6 FSI and is only five more horses than the original 3.2L V-6. However, its peak torque, 87 lb-ft more than in the V-8, comes at a mere 1750 rpm-and you can't even get to all of the V-8's 324 lb-ft until it reaches 3500. Not only that, but the diesel's 17/25 city/highway fuel economy is the best of the three (VR6 is 14/20, V-8 is 13/18) and is comparable to the V-6 Malibu's (17/26) and the same as that of a Honda Accord V-6 manual. Unlike the Malibu or Accord, though, this VW will tow 7700 pounds.
And it's clean, too: the Touareg V6 TDI meets Tier 2, Bin 5/ULEV II standards. The diesel uses a common-rail system with piezo injectors and a new catalytic converter system. Ensuring the clean-diesel status of this vehicle, Volkswagen implemented DeNOx, which uses urea to reduce emissions by up to 90 percent. AdBlue (32% urea, 68% water) is sprayed into the exhaust gas stream before it reaches the DeNOx catalyst, where the urea converts NOx gases into nitrogen and water. The amount of AdBlue needed to be sprayed is monitored by a NOx sensor located after the DeNOx catalyst.
The AdBlue is stored in a 4.5-gal tank in the rear of the vehicle, and the refill spot is under the compact spare. Initially, the idea is that dealerships will refill the AdBlue tank during standard scheduled maintenance (a "service engine soon"-type light will appear 1500 miles before AdBlue runs out, and a tank should last 10,000 miles), but owners may be able to do it themselves in the future. A warning to procrastinators: Government mandates will not allow diesels that use urea injection to run without; when it's time to add more, don't ignore the light. Whether it's the ML, X5, Q7, Touareg, or any other diesel that uses this system, when the tank is empty, the vehicle will not restart. Period.