After engine run routine maintenance

Some of the combustion byproducts can get in through the waste oil in the muffler draining back into the engine. Also, nitric acids are formed any time AIR is used in combustion.

WHAT water droplets? I have opend hundreds of engines and NEVER saw a water droplet. Besides, once the oil is on the parts, water will not penetrate it unless it breaks down.

What a lot of this means to me is one thing:

Rust is not predictable and no matter what you do, you may or may not get rust!

Well, Paul, you must never have opened and engine from South Louisiana... I've seen MANY with condensation on the innards... One thing we gots plenny of is hoomiditty...

Bill

Move to Myrtle Beach, South Carolina or Miami, you will get water in the crankcase. The water will mix with castor and fuel, but not with your petroleum after run oils. A bit of castor oil mixed well into any remaining fuel in the engine seems to work well in very humid climates. Like when sea fog rolls in almost every morning. Condenses on and in everything.

I have worked with corrosion protection enough to know that rust is very predictable. Take soft iron add an electrolyte (it must conduct electricity) with enough disolved oxygen in the water and you can see it rust in front of your eyes in just a few minutes. Sea Fog is just that a fairly good electrolyte with lots of oxygen. But disolve the water in fuel and oil and it is no longer a good electrolyte.

Well, considering that no common engines have any soft iron in them, that kes a lot of sense.

Based on the sum total of responses here, rust in model aircraft engines isn't as predictable or preventable as some seem to think

Ok, is that a definite enough ststement for you?

If water doesn't mix with petroleum oils (NOT a true statement) then they would be far better than something that it DOES mix with. Residual alcohol is often cited as the main culprit because water mixes with it.

Preventing rust is 90% keeping the water away from the steel. The other 10% is neutralizing the acids and other chemicals that get into the system through various means.

It seems to me that a safe addition would be: Using fuel with at least some castor oil improves the chances of avoiding rust.

-- Jim in NC

Paul, I store my engines in the planes, which hang from the ceiling of my air-conditioned work room. The AC is on from April through October, generally.

I store my engines the same, whether using after-run oil or not. John

Like I said, storage location may have more influence than actual procedure.

What are you using for after run oil? Seems like something to avoid if it is doing that.