"30 mpg city, 34 mpg combined, 42 mpg highway"

These are the EPA's estimates of fuel economy in the 2011 Volkswagen Jetta TDI equipped with the 6-speed DSG automatic gearbox, like our long-term test vehicle that we call Olga. We've certainly spent plenty of time testing and reporting on this diesel-powered sedan's light appetite for fuel, especially on the highway where Olga really shines. Why all the focus on economy? The TDI costs about $2,500 more than a comparably equipped Jetta with a 2.5-liter gasoline engine. Plus, diesel prices are about $.50 more per gallon than regular unleaded gasoline (national average at the time of writing.) This means that, to break even with the less-efficient gasoline Jetta, the TDI has to return some pretty impressive economy.

Of course, this diesel engine has merits of its own that justify its premium price, especially when mated to this dual-clutch transmission. Olga's output rating of 140 horsepower may not seem great, but the torque, a stout 236 lb-ft, makes the diesel feel positively quick. That torque allows the TDI to cruise quietly at highway speeds, a characteristic not shared by gasoline engines of similar size.

The turbocharger creates minor lag and upshifts are a bit early with the transmission in the normal "D" setting. But the DSG transmission allows the driver to shift manually or select the excellent "S" setting, which upshifts later and downshifts earlier for a sportier experience. The joyful combination of the turbodiesel and the DSG may be enough for enthusiastic drivers to select this combination regardless of the Jetta TDI's price premium. This driver is certainly a fan after a week with the vehicle.

More often, though, drivers will expect the diesel's economy to pay off. So what kind of economy can you really expect? Does a fuel-conscious driving style pay off in the TDI? To answer these questions accurately, one cannot depend on the Jetta's handy trip computer. Only calculating the exact amount of fuel consumed can provide precise economy numbers.

I measured Olga's fuel economy in three tests: combined city/highway driving with a normal driving style; combined city/highway driving with an economy-minded driving style; and highway only.

Both combined city/highway tests included an even mix of urban, suburban and interstate trips. In the first, I drove with no regard for economy, operating the vehicle as I do in typical driving and enjoying the occasional acceleration sprint. In the second, I accelerated softly and kept speed down, but otherwise did not employ "hypermiling" techniques. In the highway segment, I kept up with traffic, running the Jetta at 5 to 10 mph above the speed limit, which ranged from 55 mph to 70 mph on my stretch.

  • Combined, normal driving: EPA Estimate - 34 mpg; Jetta computer display - 34.9 mpg; actual observed fuel economy - 36.5 mpg, 7% greater than EPA estimate
  • Combined, efficient driving: EPA Estimate - 34 mpg; Jetta computer display - 41.7 mpg; actual observed fuel economy - 43.7 mpg, 29% greater than EPA estimate
  • Highway, normal driving: EPA Estimate - 42 mpg; Jetta computer display - 48.0 mpg; actual observed fuel economy - 47.5 mpg, 13% greater than EPA estimate

These results are significantly better than the EPA estimates. Plus, the numbers show that economy-minded driving can return nearly ten extra miles for every gallon of diesel fuel, compared with the EPA's estimate.

Because a variety of factors like topography, weather and vehicle load can affect fuel economy, apples-to-apples comparisons remain challenging for car shoppers. EPA estimates provide a sensible way to compare different vehicles, but they don't always tell the whole story. Shoppers seeking high fuel economy may be better off narrowing their search to a specific economy range, then using other factors, like vehicle styling or driving characteristics, to make a selection. Vehicles with small gasoline engines and hybrids compete in Olga's territory. For this driver, I'll take the versatility of the diesel over a weaker gas motor or a more complex hybrid drivetrain.

Olga continues to hold up well to our use, although one of her wheel center caps managed to jump from its home onto my driveway during the night. Close examination revealed that the plastic tabs that secure it in place were broken. I ordered a $10 replacement part online for an easy and inexpensive fix.

author photo

Nick Palermo is an automotive writer and lifelong car nut. He follows new and late-model used vehicles for AutoTrader.com, writes about vintage cars for Hemmings Classic Wheels and blogs on all things automotive at LivingVroom. He lives in Atlanta with his wife and twins.

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