You seem to be confusing volatility with susceptibility to detonation. These are two different things. Diesel fuel is relatively non-volatile, so it doesn't vapourise easily and thus is hard to ignite, but it has a low octane rating, and will suffer badly from detonation in a petrol engine. Butane illustrates the opposite case. Its highly volatile, so its easy to ignite, but it has a fairly high octane rating, so it won't suffer badly from detonation in a petrol engine. The people in this thread (apart from me, of course, but my query is ignored ) seem to be suffering from the same confusion, so don't feel bad. http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3964478/HerrStig#Post3964478 Re the valve sealing, you might be right, dunno. Some 2-stroke oils (notably castor, as an extreme "classic" example) polymerise on hot surfaces. This is discussed in the Forumosa thread I linked to above. I suppose this could have some cushioning effect, but I'd think it'd burn off the exhaust valves very quickly. It might accumulate on the intake valves, but I dunno whether I'd expect such deposits to seal better than the ground-in valve seats. They might actually be worse, creating high spots, for example.