is it true that you can run a diesel engine on vegetable oil and a few drops of turpentine?”
Yes you can, but you don’t need the turpentine and you need to modify the diesel engine to use the vegetable oil. I just recently inspected a veggie oil GMC hippie bus at a Whole Foods Store. It had rows of huge filters, a pre heater to make the oil hot, AND a separate diesel only tank to start and shut the engine off. You can’t start an engine with vegetable oil, it won’t burn until the engine is already running. AND, you can’t shut off a diesel engine with vegetable oil inside it, because it will congeal like grease and clog everything up. SO, you must run the engine a little with regular diesel fuel before shutting the engine down to prevent this. Needless to say, this is a relatively complex set up, so don’t just go and pour vegetable oil into your diesel tank.