Hi guys,
perhaps a stupid questions but i haven't found the answer after searching, can I used simple castor oil such as this one to add to the fuel for my initial breakin tanks, or do I have to buy some sort of specialized castor oil?

thanks!

I would go for some castor racing oil. Thes medical health oils have other specs than high end lubrications. Mostly some parfume is added as well if it is a body oil....

Pharmaceutical-grade castor oil sold as a laxative works great. It's completely unprocessed and has no additives. It isn't even de-gummed, so a small amount added to your fuel will allow a thin film of varnish to form over time, sealing scratches in the piston and cylinder. It's expensive vs. industrial-grade castor oil though, since it has to pass extra purity tests, but I haven't found unprocessed industrial-grade castor oil in a long time -- it's all degummed nowadays, because people are willing to sacrifice a little bit of extra lubrication in exchange for lower maintenance.

That being said, while the pharmaceutical-grade stuff costs more per mL, you really don't need much. I run Byron's Gen2 fuel with 11% oil premixed, and I add 43mL of pure castor oil per gallon to raise the oil percentage 1%. I can spike about 2.5 gallons of fuel using one small bottle of pharmaceutical-grade castor oil from my local drug store.

But yeah, don't use castor oil intended for skincare unless it specifically says it contains nothing else.

All castor oil that is virgin first pressing is the same oil. Medicinal castor is refined a little more (filtered tighter). It's all the same oil. Very little second/multiple pressing oil makes it into liquid oil production. A lot of that is used in cosmetics and stuff. I've used castor from fuel companies and apothecary companies alike. Same weight, color, smell, and performance in engines. Medicinal castor is more expensive, but if all you're doing is spiking your fuel, it's fine. If using medicinal castor, ensure it has no additives or sugar in it. Racing castor - like Klotz Benol - is a polymerized castor and as such isn't virgin castor. It will not mix with some fuels - such as O'Donnell's speed blend. Stick with virgin castor and you'll be fine.

I buy two gallons at a time from bulkapothecary.com for $17/gal. it works as well as the castor from SIG and S&W fuels.

Thanks for the info, seems like this one should do the trick

Except that stuff is ridiculously expensive. But it should work. Most if not all castor oil is organic too, FWIW. Save yourself a little money. Try this:
Castor Oil | Bulk Apothecary

Interesting, I didn't know that polymerized castor oil doesn't mix with nitro fuel, but now that I think about it, it kinda makes sense. Polymerization is what happens to castor oil when it heats up to its smoke point -- that's how it forms varnish.

Polymerizing is merely the substance chemically changing due to any number of factors. All you have to do to polymerize castor oil is to heat it to about 400F for a number of hours. This changes the chemistry of the oil so it will mix with other solvents - like gasoline. In the case of castor varnish - the varnish will form at temperatures below the smoke point, but many don't realize that the varnish continues to lubricate. This varnish is what keeps ferrous technology engines "alive" for so long. (Ferrous technology engines employ a Meehanite piston in a hardened steel cylinder liner with minimal taper) The varnish provides some of the piston sealing. I don't see much varnish formation in car engines, but definitely see it in aircraft engines - mainly due to the higher operating temperatures and extended high throttle usage.

Benol will mix with some or most glow fuels, but I've seen pictures of people adding Benol to O'Donnell's fuel and it acted like oil and water - not miscible in that particular fuel. Why - I'm unsure. I don't leave anything to chance - I won't use Benol. I'll almost guarantee virgin castor would mix though. Castor oil has been the oil of choice for decades and there are thousands of engines operating today that were new 30 years ago that still perform as well today as they did back then because of the castor oil. In many of my engines, I use a full castor diet free of any synthetic oil - including 4-stroke cycle engines. They run well on it and carbon is rarely an issue.

I have Eurol Racing 1
It is a very good racing oil to mix fuels with and works very well to mix som extra with excisting fuels. We also use it to rebuild engines.

I noticed we have that oil here too, might be a good choice when the trusted Castrol M isn't around anymore.

That's O'Donnell, not the Benol that's at fault. It will react to pure castor as well.
Far from all castor racing oils are polymerized, it's the ones they want to add mineral oil to that needs to be treated, but they still don't work with any additional mineral-based oil.

It seems very strange to me that O'Donnell fuel would reject castor oil, unless O'Donnell fuel isn't made from the normal ingredients of methanol and nitromethane. Castor oil is used in methanol fuel because it is uniquely good at dissolving in alcohols; most oils don't dissolve in alcohols very well. So for O'Donnell fuel to reject castor oil, there must be something very strange about its formulation. Maybe it's already saturated with some other type of oil and it can't hold any more?

Well, racing castor is still castor at heart that's had stuff done to it or added to it. If it hasn't had anything done to it or added to it, then there's nothing more special about it than the stuff that makes you poop easier. Heck, they could out the word "racing"'on the laxative bottle and sell more of it?

Benol isn't regular castor is the point I was trying to make. It's expensive that has other stuff added to it and its chemically changed from the base oil. Mix it with gas for your go kart, not model engine fuel. IMHO.

I get you!
They do print all sorts of stuff on things though to sell more, like mineral water that's just plain old water.
Some additive packages can be in the 0,1% range, it all depends on what they are trying to do, or adapt it to.

BeNol is altered, but buying an altered castor oil can be the only way for a regular person to get a hold of some of the additives that may be of benefit.

The guys working with tribology isn't exactly dumb people, they have quite a few years in school.
But of course, if they have developed something for door hinges, it might not be suited for airplanes.

I have no idea what they have used in the fuel, but regular castor oil will leave a brown sticky surface in fuel bottles etc when mixed with O'Donnell.
It's not what I would call a proper racing fuel anyway, that stuff don't work when you start pushing things.