On Thu, 20 Dec 2007 08:21:32 -0800 (PST),
wrote:

On Dec 20, 6:04 am, Denny wrote:
The biggest killer of aircraft engines is dry starts
from weeks/months of sitting between starts...


That's one, but there's another bad one: Short flights,
especially in cold weather. byproducts of combustion include water
vapor, and some of that squeezes past the pistons and rings when the
engine is cold (some when it's hot, too, but much less so) and this
vapor condenses in the crankcase and ends up in the oil. If the engine
doesn't get hot enough for long enough, the water isn't boiled off and
will mix slowly with the oil, breaking it down and combining with
sulfur and chlorine and nitrogen to form sulfuric, hydrochloric and
nitric acids. These don't belong in your engine. The stuff that's left
from these reactions forms sludge and clogs up hydraulic lifters and
cakes on the inside of the case and soon enough breaks off and shows
up as scary black guck in the filter. The acids cause dissimilar metal
corrosion between the crank and cam and their bearings, between the
aluminum piston and the steel cylinder and rings, and on valve stems.
Bad. Corroded valve stems break and the engine tries to eat the valve
heads and gets indigestion.
The oil in my little old Continental doesn't get above
120°F on cold days. There's a tank blanket that I need to buy or make
to get it up. I just finished rebuilding the thing to fix corroded
bearings and seized valve lifters.

Dan

as a matter of deep religious significance, once your engine is warm
start the clock and dont land until an hour is up at least.

in the depths of winter remember that some parts of the world need
global warming :-)

now to be serious...
squeezing past the rings probably contributes a millionth of one
poofteenth of a percent to the problem.
when the crankcase cools there is moist external air sucked into the
cavity of the case through the crankcase breather. the moisture
condenses onto the cold internal surfaces of the engine.
can you please factor that into the alchemy above? it probably does
the damage occurring between the poofteenth of your scenario and the
100%.

now if you really want scarey black gunk try taking off the oil
reservoir and cleaning it out.

honestly you must lay awake sleepless at night :-)

Stealth (the O-200 is king) Pilot