Yesterday I found myself in a traffic jam on Route 290 near Worchester, MA, behind a guy in an old Mercedes who was apparently burning used french fry oil for fuel. Two things I noticed: 1.) the car seemed to smoke excessively, especially at low engine rpms, and 2.) that stuff really stinks! If I ate at fast food restaurants maybe it wouldn't be so bad, but I got pretty nauseated before I was able to get around him. It was an old Merc so maybe the engine was shot or out of adjustment, but I wasn't particularly impressed with the whole arrangement.