...after more than 2,000 miles on veggie oil, there seem to be few disadvantages to the transformation. My car seems to get slightly better mileage, it seems to run a little more quietly and it has just as much zip as it does on diesel. According to test results I’ve seen, vegetable oil burns somewhat cleaner in most categories than diesel fuel, and emits absolutely no sulfur. What a veggie car does emit is a smell faintly redolent of the kind of oil being burned — or, in the case of used oil, the scent of whatever it might have cooked previously. Vegetable oil, of course, is a renewable resource that emits no more carbon dioxide than next year’s crop will absorb and requires no drilling for soybeans in the Arctic National Wildlife Refuge or anywhere else. The environmentally aware will give you even more points in the game of green for using oil previously used for cooking.