GOING GREEN :  I am going to do my part; in this GREEN Month of March 2009 I will be changing my work vehicle to the VERY GREEN  Volkswagen Jetta Wagon TDI Diesel

Official Energuide fuel economy figures for the 2009 Jetta TDI sedan are 6.8/4.8 L/100 km city/hwy (manual transmission) and 6.8/4.9 L/100 km city/hwy (DSG automatic). My test car had the optional DSG transmission, and over a week of careful driving using fuel-efficient driving techniques, I managed 5.7 L/100 km (50 mpg Imperial) which is almost exactly Energuide’s combined rating.

Apart from the driver’s skill, two key features of the Jetta TDI make it possible to attain this excellent fuel economy: the turbocharged engine’s generous torque at low revs, and the six-speed DSG automatic transmission. The diesel engine’s healthy torque enables the Jetta TDI to cruise along and even accelerate up hills without the engine going over 2,000 r.p.m., and when driven gently, the transmission will shift up before 2,000 r.p.m. Similarly, cruising on the freeway, the engine revs at just 2,000 r.p.m. at 100 km/h in sixth gear. The lower the engine revs, the less fuel it uses.

2009 Volkswagen Jetta TDI. Click image to enlarge

This is unlike non-turbocharged gasoline engines that often develop maximum torque in the 3,000-4,000 r.p.m. range. The Jetta 2.5-litre inline five-cylinder engine, for example, develops its maximum torque at 4,250 r.p.m. Its Energuide fuel consumption rating is 10.7/7.2 L/100 km city/hwy.

The other benefit of the 2009 Jetta TDI’s generous torque is quick acceleration in the 0 to 80 km/h range. With maximum torque developed so early, the Jetta TDI just flies off the line, pressing the driver back in the seat with a sensation similar to that of acceleration in an electric car or a hybrid with the instant low-end torque of an electric motor. The six-speed DSG transmission shifts quickly, smoothly and often, a perfect complement to this turbocharged diesel engine. It’s also possible to shift manually using the DSG’s sequential Tiptronic shift mode, or put the Transmission lever into “S” mode where automatic shift points are delayed for better acceleration. However, with a 4,500 r.p.m. redline, the 2.0-litre TDI engine doesn’t have the “legs” of a typical gasoline engine, and highway passing is more of a challenge.

Driving aggressively won’t help your fuel economy though, and I would expect energetic driving techniques to increase the Jetta TDI’s average fuel consumption by one or two litres per 100 km.

The new 2.0-litre TDI engine is quieter than the old 1.9-litre TDI engine, and the annoying rattle of the diesel engine’s high-compression combustion ignition process is more of a background sound in the new Jetta TDI. The new engine is clean too: you can’t smell the diesel fumes and there’s no black smoke coming out of the tailpipe.