[shiresoft]

Actually in the case of biodiesel, the vegetable oil is processed so that it is chemically closer to diesel than the source oil. Biodiesel is produced from the source oil through a process called transesterification.

I would avoid directly using vegetable oils in a modern diesel engine (especially recycled vegetable oils) due to the high concentration of "free fatty acids" which can cause internal damage (especially to the injectors). The transesterification process (and associated purification steps) will result in something much more palatable to modern engines (but still not covered by most OEM warrantees).