Fuel for Fox 40 sport

Question, can I run 10% 50/50 (caster-synthetic) in a Fox 40 sport engine. The engine has about 1 hour on it. Fuel is hard to find here in Idaho Falls and I happen to have some of the above mentioned fuel on hand.

If not, can I make up a blend that will work. I was thinking about some 15% stuff and adding caster, I would still have a blend of synthetic but the caster content would be up and the nitro down a bit. Any suggestions?

LL--

Fox instructions say fuel with 17%-20% CASTOR. No mention of blends with synthetic... The iron piston and leaded steel sleeve engines need a bunch of castor, and synthetic detergent oils sometimes keep the piston-cylinder parts TOO clean. Shouldn't be as much problem with the small case 40 schneurle, made mainly for the RCers -- what isn't?--

I'd be more comfortable with the recommended minimum of 17% castor plus 3%synthetic, than with a 10%castor-10%synthetic oil portion. That's if your total oil were to be 20%...

Luck!

There was a time when most of the magazine engine columnists were recommending synthetic for everything. Fox instruction manuals were rewritten to state that using synthetic voided the warranty. Several other manufacturers soon followed suit. I think they really only enforced this for all synthetic. They might have allowed 50/50. I remember a few years later Fox loosened up to state that the fuel had to have a larger proportion of castor. Personally, when I buy blend, I add about 4 ounces of Baker's anyway. I'd prefer to spend a little extra time cleaning a plane than replacing an engine after a short overheated run without it. Castor has about a 25 degree higher flash point than the best synthetic oil suitable to mix with nitro/methanol.

LL--

In addition to what Tony O said, that varnishing problem -- that F4F Guy blasted (quite correctly)re precision fitted chrome (or nickel) sleeves/high silicon aluminum pistons -- works differently in iron in steel engines.

The porosity of the cast iron "holds" a certain amount of the "varnish", which (I wish I could recall the source so I could evaluate the usefulness of this) I recall at least one mention of changing to a lubricating state at running temperatures and rates of motion. Self-adjusting and self-renewing "sheath" of lube, in effect.

Anyone remember who and where got that description started?