How we tested

To modify the Jetta to run on used cooking oil, we bought a $795 kit from a company called Greasecar (www.greasecar.com). It included a 13-gallon auxiliary fuel tank for the cooking oil, hoses and fittings for rerouting the engine coolant to warm the veggie-oil tank, extra fuel lines, a special inline filter, electrical components, and switches. We supplied some missing wire needed to correctly complete the installation.

The involving installation is best suited for proficient do-it-yourselfers and professionals. Because the auxiliary fuel tank is mounted in the spare-tire well, displacing the spare, we had to drill holes in the trunk. Properly routing and connecting the new fuel lines, heater hoses, undercar wiring, and dashboard switches required hands-on skill. One of our certified mechanics spent about 10 hours to complete the job, using our well-equipped workshop.

We also installed two more 5-gallon auxiliary tanks so we could test multiple fuels. One of the extra tanks held B100 while the other contained B5. Including the petroleum diesel in the main tank, we had four different fuels on board for comparison tests.

We made arrangements to pick up used fryer oil from a couple of local restaurants for free. Collecting, filtering, storing, and fueling became a much greater chore than performing a simple gas-station fill-up. We collected it in covered pails and filtered it through a large paper paint filter to remove any food residue, which was a messy chore. We then had to use a funnel to pour the oil into in the tank in the car's trunk.

Our instrumented tests measured performance and pollution. We conducted our standard tests for real-world fuel economy and acceleration, measuring 0-30 mph, 0-60 mph, and quarter-mile times. To measure tailpipe emissions we contracted with a Connecticut emissions test station. That facility measured the output of Hydrocarbon (HC), carbon monoxide (CO), oxides of nitrogen (NOx), and particulates.