Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I’d get off the two stroke oil if possible. That’s the soot, just like you’ll get on the tail pipe of a two stroke bike or leg of an outboard. I’m not seeing much of it from my M91 using a fair bit of marvel mystery oil. Bog standard hydraulic fluid would also work. It’s designed for fairly high heat, high pressure in applications such as high speed hydraulic pumps and rams subject to far worse abuse than our engines. It will leave a bit of slippery slime, but not black, and won’t gum up in storage. A hint of how well hydraulic oil handles combustion. I’ve used it as a bore preservative inside black powder guns, and after a good post firing swabbing, they’re still oily.