Originally Posted by hawthorne90250

Biofuels aren't always as clean as they're cracked up to be, said John Swanton, an air pollution specialist with the state Air Resources Board. The reclaimed grease generally emits lower levels of particulates, he said, but still releases significant amounts of other pollutants, such as nitrogen oxide.

Although wannabe green drivers have good intentions, he said, "These kinds of modifications tend to lengthen the lifetime of the older diesel vehicles that we would really just prefer be retired."