Some phuel photos phor here soon.
First off, where are you? Just curious. And where'd you find me? Just curious, again.
Both should run on fuel that's at the very least 20% oil, and at least half the oil should be castor if possible. Most of the plastic
fantastic RTF 'hobby' shops have fuel, but not good for half-A's. I can't tell you a brand, as I don't pay any attention to fuel on the
shelf since I always mix my own. Not because it's any better mind you, it's just always 'fresh' when I make it for a contest or test
If you can find fuel that's 20% oil and it's pink, chances are it's all synthetic. It might say if there's castor in it. In any case, for
a tender old buggy and a Testies car...Testor's(!) motor should be pretty happy on the same fuel.
For some 20% oil fuel (make sure you're seeing oil not Nitro - though Nitro is good from zero to at least 40%), I'd mix castor in
and above the 20% to make it 25% just to be sure these little motors are oiled well enough.
8 ounces of castor oil to a gallon of 20% oil makes it right at 25% (24.7) which is a good number I think. Finding 25% oil fuel that's
half castor and half synthetic would be better, but take what you can get. Of course, 2 ounces of castor for a quart of fuel works
out the same.
You can get the raw materials, but not always easily available anywhere. Klotz synthetic oil is available at most any motorcycle shop.
There are two: KL 200 is 100% synthetic, KL 100 is 20% castor. I like the straight stuff as it's easier to do the math. Same place
will likely have castor oil, too. See Klotz 'Blendzall' brand. It's 100% castor oil. I'd not take any substitutes unless a hobby place
has the stuff Sig packages (It's Klotz under the Sig label). You can mix the oil, and find the alcohol much more easily than Nitro. Try
the Yellow Pages under Chemical Supplies and the like.
Guaranteed, others have their own brew. I've been known to run 70% Nitro, 5% propylene oxide*, 5% Alky, and the balance 20%
50/50 oil. Not good for them, but they may go really fast assuming the motor is set up to run on it.
If you happen to be close by, I'd be happy to stir some up for you.
Thanks for the question. I think I should put something about fuels on my Web site.
Anything else that I might venture a guess on for you?
*Nasty, nasty stuff; only for the foolhardy who really, really want to go fast.
The next item will speak to going fast with 80/20.
From our dear departed George Aldrich about castor oil:
CASTOR OILBy Bert Striegler.
Rescued from George M. Aldrich's web site, now closed down, after his passing away. Some edits and additions by Göran Olsson.
Back in 1983 there was quite a controversy in Radio Control Modeler magazine about the tests that were necessary to measure the "lubricity" of various oils that might be useful in model engines. Castor oil was used as the benchmark, but it was obvious no one knew why this was so. They apparently got a lot of info on various industry tests of lubricants, but these were really designed for other purposes. This was my answer. I will remind you that I was a lubrication engineer and not a chemist, but I drew my chemical info from Bob Durr, the most experienced lubricant scientist in the labs at Conoco. Bob worked with my group on many product development projects and I can tell you that he is one smart hombre! Small changes were made in the text, but surprisingly very little has really changed since this was originally written. Here goes with the answer:
"I thought I would answer your plea for more information on castor oil and its "film strength", which can be a very misleading term. I have never really seen a satisfactory way to measure the film strength of an oil like castor oil. We routinely use tests like the Falex test, the Timken test or the Shell 4-ball test, but these are primarily designed to measure the effect of chemical extreme pressure agents such as are used in gear oils. These "EP" agents have no function in an IC engine, particularly the two-stroke model engine types.
You really have to go back to the basics of lubrication to get a better handle on what happens in a model engine. For any fluid to act as a lubricant, it must first be "polar" enough to wet the moving surfaces. Next, it must have a high resistance to surface boiling and vaporization at the temperatures encountered. Ideally the fluid should have "oiliness", which is difficult to measure but generally requires a rather large molecular structure. Even water can be a good lubricant under the right conditions.
Castor oil meets these rather simple requirements in an engine, with only one really severe drawback in that it is thermally unstable. This unusual instability is the thing that lets castor oil lubricate at temperatures well beyond those at which most synthetics will work. Castor oil is roughly 87% triglyceride of ricinoleic acid, [ (CH3(CH2)5CH(OH)CH2CH=CH(CH2)7COO)3(OC)3H5 ], which is unique because there is a double bond in the 9th position and a hydroxyl in the 11th position. As the temperature goes up, it loses one molecule of water and becomes a "drying" oil. Another look at the molecule. Castor oil has excellent storage stability at room temperatures, but it polymerizes rapidly as the temperature goes up. As it polymerizes, it forms ever-heavier "oils" that are rich in esters. These esters do not even begin to decompose until the temperature hits about 650 degrees F (343 deg C). Castor oil forms huge molecular structures at these elevated temperatures - in other words, as the temperature goes up, the castor oil exposed to these temperatures responds by becoming an even better lubricant!
Unfortunately, the end byproduct of this process is what we refer to as "varnish." So, you can't have everything, but you can come close by running a mixture of castor oil with polyalkylene glycol like Union Carbide's UCON, or their MA 731. This mixture has some synergistic properties, or better properties than either product had alone. As an interesting sidelight, castor oil can be stabilized to a degree by the addition of Vitamin E (Tocopherol) in small quantities, but if you make it too stable it would no longer offer the unusual high temperature protection that it did before.
Castor oil is not normally soluble in ordinary petroleum oils, but if you polymerize it for several hours at 300 degrees F (149 deg C), the polymerized oil becomes soluble. Hydrogenation achieves somewhat the same effect.
Castor oil has other unique properties. It is highly polar and has a great affinity for metal surfaces. It has a flash point of only 445 degrees F (229 deg C), but its fire point is about 840 degrees F (449 deg C)! This is very unusual behavior if you consider that polyalkylene glycols flash at about 350-400 degrees F (176-204 deg C)and have a fire point of only about 550 degrees F (288 deg C), or slightly higher. Nearly all of the common synthetics that we use burn in the combustion chamber if you get off too lean. Castor oil does not, because it is busily forming more and more complex polymers as the temperature goes up. Most synthetics boil on the cylinder walls at temperatures slightly above their flash point. The same activity can take place in the wrist pin area, depending on engine design.
Synthetics also have another interesting feature - they would like to return to the materials from which they were made, usually things like ethylene oxide, complex alcohols, or other less suitable lubricants. This happens very rapidly when a critical temperature is reached. We call this phenomena "unzippering" for obvious reasons. So, you have a choice. Run the engine too lean and it gets too hot. The synthetic burns or simply vaporizes, but castor oil decomposes into a soft varnish and a series of ester groups that still have powerful lubricity. Good reason for a mix of the two lubricants!
In spite of all this, the synthetics are still excellent lubricants if you know their limitations and work within those limits. Used properly, engine life will be good with either product. Cooked on a lean run, castor oil will win every time. A mix of the two can give the best of both worlds. Most glo engines can get by with only a little castor oil in the oil mix, but diesels, with their higher cooling loads and heavier wrist pin pressures, thrive on more castor oil in the mix.
Like most things in this old life, lubricants are always a compromise of good and bad properties. We can and do get away with murder in our glo engines because they are "alcohol cooled" to a large degree. Diesels, though, can really stress the synthetics we use today and do better with a generous amount of castor oil in the lubricant mix. Synthetics yield a clean engine, while castor oil yields a dirty engine, but at least now you know why! "
Bert was the Sr. Research Eng'r. (ret.) at Conoco Oil Co. He's a graduate in aeronautical eng'rg., and a long time modeler. I never understood how he wound up in the oil research business, but I guess it's because he's just very smart ! I deserve no credit, Bert's the brain ! /George M. Aldrich