It’s also possible to make biodiesel from any animal or vegetable lipid base with a few cheap and readily accessible ingredients in a dystopian scenario. I don’t usually promote products, and I am not a dealer, I have no stake in the company, but if you haven’t looked at Amsoil I recommend it. The oil originated in aerospace and is vastly superior, and I have vetted it for double change intervals with independent lab oil analysis, change the filters at the normal interval of course. Regarding diesels, the mechanical injection diesels are the best, no automobile with a diesel made in the last twenty years is free of electronics though, so it’s a swap it in yourself deal. Hatz and Deutz both make mechanical air cooled diesels suitable for automotive applications, not cheap but insanely reliable.