We used to run straight unconverted (other than carefully filtered) used cooking oil in my Dad's 60'-ish diesel Land Rover. Worked exceedingly well in summer months, although the first year we tried it we found out the hard way that it solidifies in cool weather - the Landy didn't budge until spring that year.

The Rover seemed to have as much power, less clatter, and a much better smelling exhaust (with a hint of the fried chicken?) running on veggie power. I don't know if a more modern common rail injection system would be affected by it, but the old mechnical land rover engine didn't mind it at all. And the restaurants seemed glad to find someone to take the used cooking oil off their hands, I think they had to pay to dispose of it otherwise.
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I'm JohnMc, and I approved this message.