Originally Posted by fyrstormer

After I bought my OS wankel airplane engine, I had to get some proper fuel for it, so I bought a quart of O'Donnell 10% nitro airplane fuel. It has 18% oil, a mix of synthetic and "degummed castor" oils. According to the OS wankel engine manual, that wasn't good enough; the engine requires 25% plain castor oil. While I realize that manual was written in the 80's and synthetic nitro oils have improved since then, I don't want my discontinued novelty engine to wear-out any time soon, so I went to the pharmacy and bought some plain castor oil to add to the fuel. I calculated how much to add to bring it up to a full 25% oil content, and dumped it in. It mixed right in, just like I'd hoped it would. (it's weird to see oil dissolve in alcohol, but that's the cool thing about castor -- it's unique molecular shape makes it alcohol-soluble.)

I have a bunch of castor oil left over, so I decided to add a little bit to my car fuel too. My cars all run on Byron 30% nitro with 11% synthetic/degummed-castor oil, so I just added enough plain castor to raise it 1%, to a total of 12%. Not a big change. However, I noticed a big difference when I opened one of my engines for a periodic checkup.

The engine internals were slathered with a thick coating of oil, unlike anything I've ever seen inside them before. The combustion chamber was also slathered in oil. I had noticed the engine made a better seal when first starting-up than it had before, but I hadn't realized just how much of the plain castor oil was remaining behind. All of the moving parts worked super-smooth with all that extra oil hanging around, and there were the early signs of varnish build-up, which I have never seen with the Byron fuel before. (varnish is bad in large quantities, but in small quantities it fill defects in the metal surfaces as the engine wears, so it helps maintain compression.)

It was interesting to see what a big difference a tiny change in the fuel composition could have. I plan to continue modifying my car fuel like this in the future. Just 1% plain castor oil, about 43mL per gallon of fuel. A 4oz/118mL bottle of castor oil from the pharmacy costs about $6, so it's good for about 3 gallons of fuel. Cheap insurance against premature wear.