I have been asked MANY times what I use as an "After-Run" lubricant, and also why do I use an after run lubricant?
A model engine being run with Nitro-Methane fuel has a Nitro residue left in the engine which is highly corrosive. Also, boaters have water as an added infiltrator, and those living around salt water, double trouble. I have seen MANY solutions to this problem. One by Gary Preusse, is simple and effective (IF YOU DON'T TAKE THE ENGINE OUT OF YOUR BOAT AFTER A DAYS RUNNING). He has a small plastic fuel tank in which he keeps a mixture of Methanol and Oil. After the days racing is over, Gary starts up his engine on this small tank and runs it for a little while to thoroughly flush out all the nitro and moisture residue. After he shuts down the engine there is a film of oil on the parts.
I use a slightly different approach. I like to take the engine out of my boat after a days running and thoroughly clean the hull, re-lubricate the drive line, check for loose or failed components, turn over my engine by hand to feel the fit of the bearings, etc. This is the perfect time to flush out the engine and apply after run oil.
Here's how I mix my concoction. I buy WD-40 by the gallon. This is the MAIN INGREDIENT for my after run mixture (By the way WD-40 stands for "Water Dispersant 40"). I mix after run by the quart. At least 50% of the mixture is WD-40. Into the WD-40 I put a little of this and a little of that, assuming that one of the things I put in is necessary! I always put a little STP Engine Treatment, a little Castor, a little Marvel Mystery Oil and a little Rislone. I put in some of what ever "oil type product" I have on the shelf (Prolong, Restore, etc).
With the engine out of the boat I first spin it with the plug out, before I put in after run oil, to feel and look for any roughness in the bearings. I also listen for the "pop" from the rotor assembly showing that it is sealing well. I then squirt a large quantity of the after run mixture into the carb. I turn the front end DOWN so the mixture runs forward to the front bearing. I rotate the engine to spread the mixture throughout the engine. I turn the flywheel over quickly and turn the engine HEAD DOWN to force excess oil out the plug hole. I do this at least twice to be sure I get all the moisture out of the bearings (WD40 absorbs moisture, so I want to get all the mixture bearing water out of the engine. I put the engine in a zip-lock bag and it is ready for the next outing. If you do this preventative maintenance, you will be rewarded with much better engine life! "I now get SEASONS out of my engines rather than engines PER SEASON".
NOTE: I have now switched to Transmission Fluid. REASON.... If something can last for 50K miles in a car, it is good for our engines. :)