[cleanspeed1]

Dude, waste motor oil, waste vegetable oil, transmission fluid, hydraulic fluid, whatever.

Look up black diesel and homemade biodiesel.

Met a trucker while I was down near Texarkana that ran his rig for a year on used transformer oil from one of the accounts he was working.

Most of the commercial chassis that used these engines were based on what you are driving now, just in 1 ton versions, so everything that they used you can use.

The old mechanical engines are great for running this kind of stuff, the only time problems come up, potentially, is with the new style diesels with the piezo style injectors, but the engines from your era including the first year Powerstroke can handle goat juice.