Castor, castor/syn blend, or synthetic

Are synthetics as good or better than tried and true castor? Is degummed castor as good as old school castor (not degummed)?

Oil is always a can of worms… which is interesting for as little difference is seems to make. Modern racing synthetics seem capable and are amongst recommendations by various manufacturers.

My rule of thumb is run castor in aircooled engines, run synth in watercooled.

Worth noting, depending on the class or organization, you may not have a choice on oil. Where you do have a choice, I think the most important thing is that you use an oil intended for racing at the correct ratio for your engine application.

Interesting there is a different choice on oil type based on air or liquid cooling. Do you know the reason?

Some clubs dictate the oil you can use??? Wow, that’s crazy.

The oil rules are more common in touring type series vs clubs. Part sponsorship, part simplicity for tech.

My rationale for castor with aircooled is based around the thought that aircooled tends to see higher localized temperatures and distortion in the liner. Consensus is that castor leaves a dry lube, somewhat like graphite after it (partially) burns.

Honestly, there’s little a lot in the way of empirical evidence, but ultimately and it smells delicious :joy:

But all that said, folks have had reliability and performance with the likes of elf HTX synthetic as well.

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IAME recommends a synthetic-castor blend, Elf HTX 909.

Rotaxes use a straight synthetic Motul 800.


I agree with the smell…that harkens back to my glory days of MX. FWIW Castrol R30, 100% castor won an comprehensive test in 1973 done buy Dirt Bike magazine (Blendzall, also castor lost horribly). Oil tech has improved since then, but for the dirtynessand going stale quickly, castor is good stuff. But as good as it smells, probably synthetic is likely superior, but only speculation on my part…

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We used Motul or LEXOIL oil, both are synthetic.

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I think some people run castor oil with a Max to coke up the head bit, then move to more traditional synthetics for normal use. Don’t quote me on that please :slight_smile:


I’ll admit I’m a lubrication geek. I wondered why castor was still around after synthetics hit the street a few decades back. Before synthetics, castor was the benchmark clearly out performing petroleum oils. But, after synthetics became in vogue, I thought castor would die as it had it’s own warts, i.e. very dirty, varnish heavy, etc. I recently read the below article and it made it clear to me why castor was still around and probably still the best lubricant for kart motors. The below author makes a case for synthetic/castor blends like Maxima 927, which I have never used but considering it as an option.

CASTOR OIL By Bert Striegler.
"Back in 1983 there was quite a controversy in magazines about the tests that were necessary to measure the “lubricity” of various oils that might be useful in 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 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. Like most things in this old life, lubricants are always a compromise of good and bad properties. Synthetics yield a clean engine, while castor oil yields a dirty engine, but at least now you know why! " Bert Striegler, Sr. Research Eng’r. (ret.) at Conoco Oil Co.

Are you saying the ElF oil is the top tier in 2 stroke oils? If so what comparative testing is there you can refer too. I would interested in seeing the data.

I didn’t say it was top tier, but from what SKUSA has said, it is widely considered to be the very best karting oil. I am sure that could be because they switched to it, but it is also a good oil. In my past, I have used Motul and Yamalube. There are several other top tier oils. My feeling is, any top synthetic racing 2 stroke oil would be top tier.

If you want anything to prove SKUSA’s claim on ELF, reach out to them to see if they have anything.

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Thanks, always looking for better oil. Unforunately there usually isn’t any facts available, just opinion and speculation.

That’s why I go back to saying that it really doesn’t matter as much as one might expect. To an extent, if the engine holds together without excessive wear between your rebuild service periods you are all set. I’ve yet to see any empirical evidence that shows performance difference in oil.

If you’re working with a specific engine builder, just run what they recommend and don’t look back.

The last comparative test of two stroke oils that I’m aware of was in 1973 by Dirt Bike magazine. It was well done and the findings were pretty remarkable. Back then Blendzall was all the rage. The test proved it was a back-marker in the comparison test. Castrol R30 (a castor oil) won out overall. Klotz, and a few others were good performers as well.

I would like to see this kind of testing done again, but I’m sure the costs are high enough and most people don’t care, being happy with hype over facts.

John according to a USPKS press release, IAME is recommending that their engines use the Elf oil.

IAME representatives have indicated that this is their preferred choice of oils for engine longevity. Elf is a product of Total, and the HTX909 has been used successfully by other karting series utilizing the same IAME engines that USPKS does. In testing and real world application, the Elf product has provided superior engine wear characteristics, and has proven very usable in varying weather conditions.

Interestingly, with regard to the last statement from above “has proven very usable n varying weather conditions”, ProKart made a recent technical announcement about oil separation in low temperatures and not to store fuel in the kart gas tank. Link – Fuel/Oil Separation Maybe this applies to all mixed fuels.

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USPKS was running Xeramic for a minute, but there was a real issue with oil separation at any temp below 50-60 degrees ambient, and it was gumming up carbs and fuel lines. We were all pulling carbs and flushing the fuel line every night, and then mixing up fresh fuel minutes before going out on the track to alleviate it. I know some people had the oil separate in the 20 minutes it took from them to mix it, put it in the kart, go to the grid, and go on-track.

Everything I hear from engine builders is the Elf stuff leaves the engine looking like new inside, and so far there have been no separation issues that I’ve seen. Builders seem to like the oil.


Can you recall what kind of testing they did, or what was noted with regards to R30 working better compared to Blendzall.

Any idea on how the ELF 909 compares to the ELF 976. They are both designed for 2strokes, however only the 909 is the spec oil.

Actually I could post the whole test as I saved all my magazines.

The basic parameters were hp, cyl head temp, EGT, wear, and a couple other measurements. If memory serves, Blendzall did ok in hp area, but wear was way out and temps were out. They tested 3 or 4 formulations of BZ, the green, gold, and one other I believe. All three formulations performed differently. If you are truly interested I can try to dig out the articles, 2 issues, and try to post them here. It could take awhile for me to dig them out. On a side note, Castrol R30 performed great, Castrol R40 performed worse than R30. In the grand scheme it is such an old test the data is worthless now as I’m sure all manufacturers have changed their formulations.

I just wish manufacturers would provide more data on their product. They clearly could as they have it available. But if no one else does there is not incentive to do so.

Data sheets on both the HTX 909 and 976.

Like always there is very little available from the manufacturers.

Flash point is higher on the 909…