Re: Water in our oil, or just alot of hot air?


<rustylycoming@xxxxxxxxx> wrote in message
news:1145736410.567086.175970@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I just watched a program about the huge Oresund bridge between Denmark
and Sweden, and there was a segment about how the corrosion problem for

the bridge was dealt with. Instead of painting, they use sealed
compartments that have the air humidity kept below 60%. This they said
eliminates corrosion. This started me thinking about the corrosion we
aircraft owners are told to guard against, since I have personally been

told by an overhaul shop, that half of all the engines he sees that
need work, need it because of corrosion. There are several "facts" that

I am beginning to question as to their validity. The ones that come to
mind are:

1) You have to get the oil up to 180 deg F or the water in the oil
won't evaporate.

The water in the oil will obviously evaporate at lower temperatures.
However, when you run the engine it puts combustion byproducts into the
crankcase. ( There is always a bit gets by those rather sloppy piston
rings. ) These byproducts are the oxidized or "burned" results of burning a
hydrocarbon fuel. Burnt hydrogen is H2O or water. Burnt carbon is CO or
CO2. These wind up in your oil as a result of running the engine. The
trick is to get the oil warm enough so that they evaporate away FASTER than
you add them into the mixture. Then you will get the water out of the oil
and avoid the formation of the organic acids that will cause corrosion
inside the engine. Minor surface corrosion that is irrelevant on the
outside of the engine may be much more serious on the inside. Yes, I have
overhauled more engines because of corrosion than because of wear.

Running the engine for a few minutes on the ground will add to the water and
other corrosives in the oil. Then you turn it off and let it work on the
guts of your engine. Do that if you want. I do overhauls quite
reasonably.

Running the engine for a longer time until the oil is warm enough to
evaporate off the water on the ground? That is not so good either. By the
time the oil is warm from ground running with most aircraft engines the
cylinder head temps are going off scale and you are beginning to cause other
problems from overheating. Look at all the guys shutting down from
overheating while waiting in line for takeoff at Oshkosh after the airshow!
:-)

If you go ahead and go flying, at least a little bit, you both warn and
distribute the oil and cool the engine. Why not go flying anyway. Isn't
that what you have the airplane for? :-)




2) Starting and ground running the engine for a minute or so is the
"worst" thing you can possibly do.

See above.


3) Flying for an hour will "clean" the oil (or at least evaporate the
water, preventing acid formation) so that it doesn't turn to acid and
dissolve the engine while sitting idle.

See above.


There are probably some others, but these three stand out the most

to me. Now I am sure that what I am about to say will not go over well
with some people, but I have the asbestos suit ready and waiting.
My take is that these three "facts" are a bunch of poppy***. Why

or how they got started is anyone's guess, but the reasoning behind
some of them is understandable, for others I wonder what they were
smoking at the time. My thoughts are along these lines, and I admit I
could be wrong, but I don't think so.


You are wrong. Sorry.


Concerning fact #1...Why does someone think that the water has to be
brought to a boil before it will evaporate. Water evaporates very well
even at sub-freezing temperatures,much less at the warm to hot temps
created in a running engine. And at say 140 F, I can't help but believe

that any water or moisture in the engine will be purged quickly. With
water at that temp you can literally see clouds of vapor escaping, and
this is well below boiling. Not that the hotter the engine gets the
water doesn't evaporate more quickly, it does I'm sure. It's just that
in the engine cases which are open to the air at the breather tube and
elsewhere, any heat above say 85 F or so will be more that enough to
dry out the oil in the crankcase. As evidence of this, I ground run my
engine all the time and have for many years. I live in a VERY humid
climate. The oil analysis reports I have done on a regular basis by
Blackstone have never shown any trace of water or moisture. I recently
tore done the engine for rebuild after more then 15 years of perfect
service, and the cam lobes, lifter faces, and every part in the engine
was shiny and totally free from rust or any other corrosion.


See above. Lucky lucky.


Concerning fact #2.... We all constantly clean and oil many of the
things we own such as tools, etc. It is the layer of oil that prevents
the rust. I accept that if the oil is too acidic it could corrode or
"chem mill" the metal, but it takes highly acidic liquid to do that,
and the oils I use have acid buffers in them to deal with mild acidity.



Running is the only way to re-oil all the parts in the engine,
especially the cam and lifters. Just like oiling the machinists tools
that I own keeps them rust free, oiling the engine keeps it rust free I

would think.

Quite true. See above.


Concerning fact #3.... This is the one that really makes me wonder. If
oil needs to be changed every 25-50 hours, how does flying for an hour
clean it? I can't help but think that the longer the oil is used the
dirtier it gets. I guess they think that it's "really" dirty just after

starting, and you "clean" it as you fly.

Clearly you don't understand the difference between dirty oil and wet oil.
Just as combustion puts gobs of water into the oil, it also puts in some
soot, making the oil eventually turn black. Detergent oils also pick up
sludge and crud from within the engine and carry it around in suspension in
the oil. Good idea to dump it out and get a fresh start every once in a
while.
I recommend 25 hours without a filter and 50 hours with a filter.
Remember, oil is much cheaper than engines! :-)



In closing, it seems to me that many of the things we are told are
contradictory on this subject. I have witnessed many OWT come and go in

my time, so common knowledge isn't always correct. Lean of peak
operation comes to mind. Some blockheads still don't think George Braly

has it right.


And some blockheads fly in the face of experience and proven test results.
Everything we know is NOT an OWT. Most OWT's are coming from people who
only THINK they know but have no scientific data to support their possibly
erroneous observation.

For example:

Cigarette smokers often get lung cancer.

Cigar smokers sometimes get lung cancer.

Pipe smokers rarely get lung cancer.

Cigarette smokers often use cigarette lighters.

Cigar smokers sometimes use cigarette lighters.

Pipe smokers usually use matches and rarely use cigarette lighters.

All smoke tobacco products.

Clearly the correlation with lung cancer is with cigarette lighters, and not
with tobacco products.

If we all used matches instead of cigarette lighters no one would get lung
cancer any more!

I love logic.

My kid brother was a statistician for the Navy before he retired. He had a
lovely comment about statistics.

"Most people use statistics like a drunk uses a lamp post. For support
instead of illumination!"

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )



Blue Skies
Rusty



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