Regulators have approved fixes for the vast majority of cars involved in Volkswagen Group鈥檚 huge billion-dollar diesel emissions scandal, but do those remedies sacrifice significant real-world fuel economy or performance? And should you buy one now considering thousands are for sale? Good news, owners and shoppers: For the largest chunk of affected cars, the fix appears to come at minimal cost, so buy away. Last summer, authorities approved an emissions fix for the oldest batch of scandal-plagued diesel (TDI) VW vehicles, a group of smaller models with four-cylinder 鈥淕eneration 1鈥?diesel engines from the 2009-2014 model years. Comprising a little more than half of all the U.S. Gen 1 includes Cars.com鈥檚 long-term 2013 VW Jetta SportWagen TDI, which we bought specifically to test the effects of the fix. We brought our TDI to a local dealership for the mid-day procedure, which took a few hours, and we tested mileage, acceleration, and horsepower and torque before and after to see what changed. Our findings suggest you can breathe easy 鈥?and not just thanks to the TDI鈥檚 reduced nitrogen-oxide emissions. In our experience, acceleration and mileage differences with the aren鈥檛 enough to lose sleep over.
The dealership鈥檚 fix for our TDI involved hardware and software modifications. It also came with a downgrade in stated EPA vehicle mileage estimates, complete with a new printout of window-sticker ratings. They鈥檙e now 29/37/32 mpg (city/highway/combined), down 2 mpg highway and 1 mpg combined from our diesel-powered Jetta鈥檚 original EPA estimates. We observed a similar reduction in fuel economy during two nearly identical mileage loops around Cars.com鈥檚 Chicago offices before and after the fix. Previously, our VW Jetta SportWagen TDI punched above its weight in fuel economy, so we were concerned that would go away with the fix. But our Jetta continued to handily beat its EPA numbers each time. Both loops began and ended at the same diesel pump in Chicago鈥檚 far-west suburbs, racking up some 136 miles of highway, suburban and rural streets around the metro area. That鈥檚 only a short sample of fuel economy, so we鈥檒l hang onto our TDI a little longer, continuing to track fuel economy. Before the fix: Over 135.5 miles, our loop returned 44.2 mpg at an average 40.0 mph. After the fix: Over 136.2 miles (longer because of an accident detour) our loop returned 42.4 mpg at an average 34.5 mph.
That鈥檚 a difference of just 4.1 percent, or 1.8 mpg, which is reasonably close on a percentage basis to our TDI鈥檚 EPA revisions. Data came from the VW TDI鈥檚 trip computer 鈥?not at-the-pump calculations, which proved too disparate to rely on. For both loops we avoided cruise control, filled the tires to their recommended pressure, kept the windows and sunroof shut and drove in the TDI鈥檚 regular (not Sport) mode. Ambient temperatures fell within 10 degrees of each other for both tests. We also took our Volkswagen TDI to a local dynamometer facility, which tested horsepower and torque before and after the emissions fix. Results of maximum horsepower and torque, as well as the output curve throughout the rev range, were similar. Before the fix: Our best run returned 135.4 horsepower at around 3,900 rpm and 225.3 pounds-feet of torque at around 2,400 rpm. After the fix: Our best run produced 133.1 horsepower and 217.0 pounds-feet of torque, at similar respective rpm. Both results were in weather-corrected outputs running the front wheels only.
Remember, dynamometers 鈥?essentially giant floor rollers that act as vehicle treadmills 鈥?can read differently depending on style, but we鈥檙e confident these are consistent results because we used the same dynamometer, operator and calibrations just days apart. The differences were slight. After the emissions fix, peak vehicle horsepower and torque fell just 1.7 percent and 3.7 percent, respectively. Successive acceleration runs only drove the similarities home. The TDI is not quick overall, but the fix didn鈥檛 affect that. Before the fix: Our best of six acceleration runs clocked 9.75 seconds from zero-to-60 mph. After the fix: Our best of six zero-to-60 mph runs was 9.67 seconds. Both runs were conducted during similar weather conditions and straightforward pedal-down acceleration 鈥?no brake-torque starts 鈥?with measurements on a RaceLogic Vbox II GPS data logger. Volkswagen鈥檚 booklet for Gen-1 TDI owners says drivers might experience minor changes in engine torque while transitioning between operating modes (when the diesel particulate filter regenerates, for example), but we didn鈥檛 observe any performance difference in daily driving.
