Don't know whether anyone has seen this, but the Engine Manufacturers Association (EMA) issued a warning in March 2006 cautioning users to be aware of the problems that can result from using raw or refined vegetable oil, or recycled grease that have not been processed into biodiesel. You can see this at
http://www.enginemanufacturers.org/admin/library/upload/891.pdf
http://www.enginemanufacturers.org/admin/library/upload/891.pdf