The diesel Touareg is essentially unchanged from the gas Touareg, so the sole story here is the engine. Volkswagen has done a Manhattan Project on its oil burner, going over everything that could make it more appealing to customers. It's a three-horse race in the non-gasoline powerplant derby, and diesels, hybrids and electric vehicles are fighting for share. VW and Audi have thrown their bets on the filly called Oil Burner, and the next couple of years will inform us whether it can win more than 5% of the market.



To the engine, then. Sounding like something they got from the lab that created Wolverine, the compact engine block with a 90-degree V angle is made of high-strength vermicular graphite iron. Being 15% lighter than cast iron and not even 1.5 feet long, it has been fitted with aluminum alloy cylinder heads and weights 498.2 pounds.

Within that block, the common-rail fuel injection system has been thoroughly refined. Electronically-controlled piezo fuel injectors permit injection pressures of 2,000 bar (29,000 psi) and spray through eight-holed nozzles for a finer fuel mist and better, more efficient combustion. Those injectors are also lighter and have fewer moving parts, and so can move at twice the speed of previous solenoid-valve injectors. With all of that, the number of injection processes per cycle can be varied and optimized as needed.



The turbocharger, served by two intercoolers, has variable turbine geometry, with vane angles controlled by an electric servo motor. And get this: it's ribbed. The engine block has fluting to diminish vibration, and "all pathways on the engine mounts that could transmit vibrations to the interior have been eliminated." Finally, to aid engine packaging, the ancillaries and camshafts are driven by maintenance free chains mounted in back of the engine.

So, what's all that get you? A torquey little V6 that grinds out 221 hp and 407 lb-ft. That latter number comes as soon as 1,750 rpm, obviating the need for much footwork with the pedal on the right when it's time to git 'er done. 0-60 miles-per-hour is estimated at 8.5 seconds, which isn't all that bad for what is probably a 5,000-plus-pound vehicle (VW hasn't divulged its weight yet, but the Touareg V10 TDI rocked the scales at 5,800 pounds).



It's not a sprinter, obviously, although neither is it a laggard. It is the marathon – or perhaps, the ultramarathon – where this car makes its name. VW says you'll get from Kokomo to the Poconos on one tank, which is 600+ miles for those of us who have nothing to do with either locale. Strictly by the numbers, you could go 660 miles if you used every drop of diesel in the truck: the Touareg is rated at 25 miles-per-gallon on the highway, and has a 26.4-gallon tank.

In reality, you might be able to go even further. On a recent drive in the similarly-engined Audi Q7 on Audi's mileage marathon, we drove from San Francisco to Los Angeles, about 352 miles, and had a half tank left when we got home – and we weren't being kind with the footwork.



In that Q7, we never got any worse than 21 mpg and we were doing some serious speeds through some serious mountains. The Audi Q7 diesel was billed as getting 33.1 mpg on the highway, so if you're a little kinder than we were to Mr. Throttle, we're sure he and his friend Mr. Gas Mileage will be a little kinder to you.

The engine has also been designed to be kinder to the environment, thanks to its use of VW's AdBlue system. Exhaust gasses pass through a catalyst where nitrous oxide is measured, and based on that measurement an appropriate amount of AdBlue treatment is injected into a dosing module. AdBlue is 32.5% urea, and mixed with the hot exhaust it breaks down into ammonia and converts the NOx to nitrogen and water. The resultant NOx levels are reduced by about 90%.

The AdBlue tank is located under the spare tire, and is heated for cold weather climates since it freezes at 12 degrees Fahrenheit. The solution itself is non-toxic, odorless and biodegradable, and the tank holds enough for around 15,000 miles. When it needs to be refilled, that can be done during regular dealer service, and VW mentioned that places like JiffyLube will carry it.



So here we have a 50-state diesel with an earth-friendly mien. But would you want to actually drive it in any state? In real-world driving, the V6 TDI shares a number of beneficial similarities with its V10-powered (former) sibling: it is quiet, powerful and refined.

At a cruise, the engine is as quiet as church just before a service, with only the slightest hum as any aural indication that the car is actually on. It is also steady as a rock: vibrations are essentially non-existent.

The V6 is 90 hp and 146 lb-ft down on the V10, but as we piloted the two-ton-plus SUV around snaking canyon roads, it was evident that VW has done its work to make sure all available power is applied to forward motion. Even on steep uphill grades, you don't worry about losing momentum because the Touareg will pick it right back up again on demand. The ride would be best described as business casual: crisp and smart, it suits all of the sporting situations you could wish to get into in an SUV.



VW says "The 3.0 TDI produces a quiet, cultivated and harmonious sound. The hard 'knocking' and metallic rattling at partial load is history." That is true... when you're cruising. And that is what makes it all the more jarring when you get hard on the power. It's as if the sound insulation has evaporated with a flick of the accelerator. Engine noise commandeers the cabin. Under mild acceleration the noise is alright. Even under hard acceleration it isn't awful, it is simply unexpected because the contrast is so striking. We found the same thing in the V10 – get on the gas, and you can hear the horses neigh.

That was the only demerit we gave to this vehicle. The only question is whether buyers will pony up the $3,000 premium for it over the VR6 FSI. The TDI will get you more power and much better gas mileage – 3 mpg more in the city, 5 mpg more on the highway, but these days, you'll pay substantially more for diesel at the pump, and that will likely more than neutralize the extra mileage. As fine a vehicle as it is, then, is it worth it? The best answer we can give to that one right now is probably this: We'll find out.



Photos Copyright ©2009 Jonathon Ramsey / Weblogs, Inc.

Meals and accommodation for this drive were paid for by the manufacturer.