Jim Thomerson

It has been mentioned several times on this and other forums that if you run castor oil in your fuel, you have a sticky oily mess to clean up off your airplane. If you run only synthetic oil, the mess is very much reduced and much easier to remove. Why is there this difference? What do you deduce about function of synthetic vs castor oil from this observation?

Jim

Hobbsy

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I thought some about this question overnight before answering. I recently bought a used MDS 1.48 that had benn run on all synthetic fuel, the inside of the engine was bone dry, you could run a Q-tip across any surface inside the crankcase and it would remain dry. The only evidence of lube was in the rod bushings, none in the rear main bearing. As a comparison I pulled the backplate off my other MDS 1.48 and OPS 30 Maxi which had been run on Fox 5% nitro fuel with 20%-50/50 lube. These each had a small amount of lube in the bottom of the crankcase and nothing was dry in them. Like you Jim, I don't know exactly what this says but because of it I will never advocate using all synthetic fuel, not even in my YS's. I run my Saitos and Enyas on WildCat Premium and Premium Extra which have 16% and 18% 80/20 syn/castor respectively and occasionally pull a backplate, I always find a generous supply of clean, prestine, reddish oil, but fourstrokes have the advantage of not washing the oil out of the engine when they run out of fuel, except YS of course.

Thumper1

Castor oil burns at a much higher temperature than synthetic oil. Quite a bit of Castor ends up on the outside of the plane and needs to be cleaned up. There is a perception that Castor oil affords a degree of extra protection to the engine. I know guys who would never use fuel that contained Castor, and guys who would never use fuel that didn't. Personally, I use some Castor and put up with the mess.

Jimmbbo

Searching the web or RCU for "castor and synthetic oil" led me to the conclusion that a combination of the two is the best choice, since they have different strengths, both of which are useful for the engine.

Cheers!

Jim