Thanks Steve:
That is the information that I was seeking.
I was always curious to know what percentage of synthetic oil do I need to keep an engine “clean.”
Frank
When in doubt, ALWAYS refer to Randy Smith's pinned articles at the top of this forum. If the answer you need isn't there, it will be a rare situation. I wouldn't claim that 7% Klotz would prevent varnishing from castor oil, but it will help. And I haven't ever had any problems with internal varnishing, and not even much from external crust buildup.
My usual fuel choice is Powermaster 10/22, mostly because the R/C bods won't buy 5/22, so nobody ever stocked it. More nitro, better idle (maybe) because the glowplug will stay hotter (maybe). Either that, or the LHS guys push the more expensive 10% and know that "better idle" is going to impress the typical R/C bod. Basically, see what works for you, keeping in mind that too much oil isn't going to hurt your engine in any permanent way.
Steve