I have experimented with veg oil in the past, lately I've been experimenting with waste engine oil in a boiler and might be interested in burning it in the truck as well.

One thing im noticing burning it in the boiler is the deposits left behind.
white and brown caked deposits that seem abrasive. I'm assuming it's heavy metals left behind from the oil.

I'm wondering if anyone sees this on engines on injector tips or valves etc. Seems like it would wear rings and pistons out eventually.