Older Diesel engines would cope much better than anything newer in emergency situations but wouldn’t know the max gasoline mixture, rough guess I wouldn’t go over 25% gasoline and I would add motor oil to it. There have been multiple multifuel engines built over the years most being able to use up to 70% gasoline with motor oil added for lubricity with no impact on longevity of motor. They have almost exclusively been designed off of Diesel engines, with the only exception that I know of being a joint effort for the military by evenrude and mercury made an outboard that would run on anything flammable and it had spark plugs but none others do that I know of(btw don’t look for it it’s a complete dog not worth its weight even when running on gasoline like it was supposed to it was unbearably slow/expensive/heavy also nobody would be able to service it since it was sold exclusively to the military) but the trick of every other diesel based multifuel engine I know of is they use super high compression, Like 22:1 high and they add a turbo on top of it and injectors that shoot a stream of fuel instead of atomization. They were never known for economy they were almost exclusively military engines, but Most older Diesel engines will cope with a certain amount of gasoline in the fuel but would be less than ideal. I also wouldn’t stress out or go drain my tanks if I accidentally added some gas to my fuel tanks but I’d never go out of my way to add it either. I’ve got plenty of tankage so running out of fuel is nothing but negligence on my part. Now to dispel the myths and lies by the uninformed There is no chemical reaction to worry about that will blow you up if you mix gasoline and diesel, but boats built with diesels tend to not have blower motors in engine compartments like gas built boats are equipped with so that would Definitly be of concern to me. Lol Also the explanation of octane by star is 100% wrong, octane has nothing to do with explosive value and everything to do the fuels ability to resist knock. Also diesel has MUCH more explosive energy in it than gasoline does if you would like to call it that, which I wouldn’t but judging by some explanations that may be the easiest way to explain it to some so I’ll go with that.