In the past five years, a number of companies have started up that offer kits to convert your diesel vehicle to run off of vegetable oil. The main players in the U.S. are Greasecar, Greasel, Neoteric, and Frybrid. Of these companies, Frybrid is the most innovative and quality minded of the lot. Frybrid was the first to introduce a really efficient heat exchanger and a microprocessor controller that will automatically switch to vegetable oil when the system is hot enough and which will not let you forget to switch back to diesel. The components of the Frybrid system were designed to handle the most challenging conditions, so that they could be installed in a Mercedes or a Mack truck. When we converted a school bus (for our traveling circus!) to biodiesel our original Greasecar system had to be largely replaced by a Frybrid one. The Frybrid system was more expensive than the competitors, and seems overbuilt, but it is much better.
— Forest Gregg
[A clarification: This conversion kit is made for using unprocessed straight vegetable oil (SVO; straight as in straight from the kitchen) which requires a separate tank. Most biodiesel is slightly processed vegetable oil, which does not require this kit. You just pump and drive. More on Biodiesel from this Primer] — KK
With 15 gallon tank