On Jan 19, 7:48 pm, sockpuppe...{at}gmail.com wrote:

> It seems weird, the water in there. It must be absorbed from the air
> during combustion. Is that it?

       Water is a byproduct of combustion, and since the piston's
rings leak a small amount of combustion gases from the cylinder into
the crankcase, water vapor gets in there and condenses. It's much
worse in colder weather, much worse if the airplane is flown on short
flights so that the crankcase and oil don't heat up enough to boil off
that water, much worse if the rings are badly worn.
       Oil contains hydrogen, chlorine, sulphur and nitrogen
compounds. Water has both hydrogen and oxygen. All the ingredients are
there for various acids (hydrochloric, sulphuric, nitric) and if the
water and oil are left together long enough they'll make them. I think
that the presence of metal is a catalyst in the process.
        I'm no chemist. I'm an aircraft mechanic and over the years
have seen lots of corrosion in engines, mostly those that were flown
infrequently and for brief periods. My own engine suffer this. Sludge
also seems to accumulate in such engines, and automoblies aren't much
different here.
        The engines we fly hard every day in the flight school reach
TBO easily and are still in dandy shape when we take them off. Very
little corrosion inside. Very little sludge.

      Dan
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