Really dumb Newbie questions.....
Here's a repost form RCU in the fuel section...
With permission from Don Nix, President of GBG Industries Inc., manufacturers of Powermaster model fuel, I am going to reprint part of his article.
"SYNTHETIC OILS
Strong Points
Good Lubricity (it's "slick")
Little or no carbon or varnish inside
Leavs less oily mess on models
Available in a variety of viscosities
Totally soluble in nitromethane
Weak Points
When used as the sole lubricant, a greater quantity is required, which increases the cost of the fuel.
Most tend to cause corrosion if adequate inhibitors aren't added
Burns off surfaces at about 100 deg. lower temps than castor
Many types and qualities, making it hard to choose the best one
Expensive-good ones cost almost twice as much as castor oil, increasing the cost of the fuel.
CASTOR OIL
Strong Points
Great lubricity
Reduces the amount required, resulting in more power and better idle.
Will tolerate internal temperatures about 100 deg. higher than any synthetic
Almost 50% cheaper than good synthetics-reduces cost of fuel.
Great natural rust and corrosion inhibibitor
Weak Points
Tends to cause carbon and varnish build up in engine if cheap grade and/or too much is used.
Messier on models than synthetics
Somewhat sensitive to extremely cold temps. - mild separation in solution, residue on model becomes almost "buttery" in consistancy.
Insoluble in nitromethane. In solutions above 40-50%nitro, will separate unless some sort of co-solvent is used.
Generally available in only one viscosity"
(In lieu of reprinting all of the paragraphs which follow this I'll print the sentences and paragraphs pertinant.)
"If you don't see much oil on your model after flying, that tells you one of two things-or both: Either there wasn't enough oil in there in the first place, or the oil is burning off with the methonal. Neither is good. There is no way oil can burn off and properly lubricate at the same time.
Oil residue in model engines is as natural as barking is to a dog. We have to learn to live with it."
Personally, many of us at the flying field prefer 10-15% nitro with 18-20% oil, 3-5% of which is castor. We run this in both 2 and 4 strokes without any problems.
I found this article on the RCO site about a year ago. It may still be there if anyone wishes to read it in it's entirety.
Jeff