Thanks for the warning John, I won't stick the exh. pipe up my nose now! Besides, it'd be too hot anyway! I think prolong, or is it slick 50, has a high pressure zinc based ingredient too, that's supposed to bad for the rod and main bearings, supposedly causes corrosion after awhile? I use 5W-30 synth blend in my 30,000mi. vehicle, and it did "seem" smoother after prolong, but that's subjective...I didn't keep it in there after hearing about the corrosion, or some other chemical reaction w/ the lead-copper, or whatever they're putting in crank bearings these days. I've wondered about trying it in a model engine too for some time, but kinda forgot about it till now. Anybody got a sacrificial engine for experimentation? I might find one...P.S., did ya ever notice how a light bulb burns real bright just before it burns out?