Here's my latest experiment in alternative fuels: a 1985 M1009 army truck, which I've nicknamed "The General." It's equipped with a the military version of the GM 6.2 diesel engine. This is the "J-code" engine normally found in one-ton civillian pickups, coupled with a mil-spec injection pump designed for "sub-standard fuel sources." Which I'm taking to mean, "free fuel sources." So far I've tested it with several waste-fuels, including used transmission fluid (which seems to burn better than pump diesel), power steering fluid, hydraulic oil, and blends of vegetable oil with diesel up to 33%, all with no modifications and no problems.
The next step will be a second, heated tank for straight WVO, with appropriate valves, heated filter and thermostat-controlled electric final heating element. Since the truck came with dual battereies and dual 100 amp alternators, I'm leaning towards electric heating of the WVO rather than complicate my engine coolant plumbing. There's still a little room under the hood on the driver's side for all the new hardware, and the tank can ride in the bed. Mileage is already pretty good for a 5400lb vehicle (around 15mpg overall), but it won't matter when I'm driving for free! Love to have this as my grocery getter.