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

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 a

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

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

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.

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 poppycock. 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.

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.

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.

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.

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.


Blue Skies
Rusty

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

Water and oil are immisible; oil floats on water; water droplets
agregate, form globules, which sink to the bottom of the galleys and
the sump. They are effectively surrounded by oil, and the water cannot
"evaporate" because there is no way for the water droplet to reach the
air so that evaporation can take place.

When an engine is operated, the oil (and water) are heated and
homogenized, turned into a mist by the throws on the crankshaft. That
is the only time the water droplets get a chance to do the evaporation
trick, where water molecules get into the air, and can exit the
crankcase through the breather, either as visible steam, or as an
increase in relative humidity of the air leaving the crankcase.

However, the net movement of air (carrying the water mist) out of the
crankcase is propelled only by the blowby past the rings, which
contains new water as a byproduct of combustion in the cylinders which
is added to the old water already in the oil. So, it seems that the
process which removes water from the crankcase (heat, thrashing,
blowby) and the process that adds water (combustion, blowby) reach an
equilibrium.

However, if the engine oil reaches a temperature where a droplet of
water will boil, then as it does, it turns to steam, the volume
increases dramatically to where the pocket of steam will "float"
upwards through the oil, and finally burst free. This is what provides
the transport mechanism to purge the water from the oil. I dont
consider this "evaporation", rather "boiling the water out of the oil",
and yes, flying an airplane an hour a week is better than letting it
sit for months without being flown.

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

This is true on cars, for a reason that has nothing to do with the
engine or oil! It has to do with rusting out the exhaust system.
Starting the engine with a cold exhaust system and running it for a
short time means that the water that is a byproduct of the combustion
condenses onto the cold metal in the muffler and tailpipe. If you ran
the engine longer, the exhaust system would eventually heat up to the
degee that it will evaporate the water, but if you only run the engine
for a minute or two, then you will leave the exhaust full of water, so
it just sits and rusts. If you do this regularly, you will be replacing
the muffer, etc ever year or two, instead of every five to seven.


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.

Never heard this one; only the "boiling water out of the oil" one.

"mikem" wrote in message
ups.com...

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

Water and oil are immisible; oil floats on water; water droplets
agregate, form globules, which sink to the bottom of the galleys and
the sump. They are effectively surrounded by oil, and the water cannot
"evaporate" because there is no way for the water droplet to reach the
air so that evaporation can take place.

When an engine is operated, the oil (and water) are heated and
homogenized, turned into a mist by the throws on the crankshaft. That
is the only time the water droplets get a chance to do the evaporation
trick, where water molecules get into the air, and can exit the
crankcase through the breather, either as visible steam, or as an
increase in relative humidity of the air leaving the crankcase.

However, the net movement of air (carrying the water mist) out of the
crankcase is propelled only by the blowby past the rings, which
contains new water as a byproduct of combustion in the cylinders which
is added to the old water already in the oil. So, it seems that the
process which removes water from the crankcase (heat, thrashing,
blowby) and the process that adds water (combustion, blowby) reach an
equilibrium.

However, if the engine oil reaches a temperature where a droplet of
water will boil, then as it does, it turns to steam, the volume
increases dramatically to where the pocket of steam will "float"
upwards through the oil, and finally burst free. This is what provides
the transport mechanism to purge the water from the oil. I dont
consider this "evaporation", rather "boiling the water out of the oil",
and yes, flying an airplane an hour a week is better than letting it
sit for months without being flown.

How does that work for an automobile engine which is a closed system?


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

This is true on cars, for a reason that has nothing to do with the
engine or oil! It has to do with rusting out the exhaust system.
Starting the engine with a cold exhaust system and running it for a
short time means that the water that is a byproduct of the combustion
condenses onto the cold metal in the muffler and tailpipe. If you ran
the engine longer, the exhaust system would eventually heat up to the
degee that it will evaporate the water, but if you only run the engine
for a minute or two, then you will leave the exhaust full of water, so
it just sits and rusts. If you do this regularly, you will be replacing
the muffer, etc ever year or two, instead of every five to seven.

12 years, 235K miles and still the original exhaust system.

Dave Stadt wrote:

12 years, 235K miles and still the original exhaust system.

But I bet you drive it at least 3 mi each time you start it.

Very well stated.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Ben
www.haaspowerair.com

"mikem" wrote in message
oups.com...

Dave Stadt wrote:

12 years, 235K miles and still the original exhaust system.

But I bet you drive it at least 3 mi each time you start it.


That's true most of the time but it still doubles your estimate for muffler
life.

How about the moisture in auto engines without crankcases vented to the
outside world? How does it get out? Once it floats upward and bursts free,
as you say, where does it go? Don't hear about auto engines with corrosion
problems even collector cars that are only driven a couple of times a year.

Dave Stadt wrote:

"mikem" wrote in message
oups.com...

Dave Stadt wrote:

12 years, 235K miles and still the original exhaust system.

But I bet you drive it at least 3 mi each time you start it.


That's true most of the time but it still doubles your estimate for muffler
life.

How about the moisture in auto engines without crankcases vented to the
outside world? How does it get out? Once it floats upward and bursts free,
as you say, where does it go? Don't hear about auto engines with corrosion
problems even collector cars that are only driven a couple of times a year.

All crankcases are vented somewhere.

Usually to the intake manifold through the PCV valve in modern cars.

--
Jim Pennino

Remove .spam.sux to reply.

Although I agree the only way to ensure a healthy engine life is
frequent flying and frequent oil change, I somehow thinks that 180F oil
temp thing is an urban myth. If you have a plane that flies twice a
week for one hour each, getting oil change every 25 hr, and the oil
temp never gets above 160F due to an oil cooler that's a bit too
effective, I don't see any evidene that such an engine will be any more
prone to corrosion than a similarly operated engine with oil temp at
180F.

Even if you have your oil temp at 180F cruising at 7500, the temp will
drop quite a bit once your start the descend. Does it mean you will
collect a lot of water in your crankcase right after you pull back the
power? My point is it's meaningless to be obsessive about the 180F.
Just go fly often, and change the oil frequently.

Crankcase fumes are sucked into the induction manifold (and burned by
passing through the engine) via the Postive CrankCase Ventilation check
valve.

Running an engine on the ground is bad. It's boring and wastes gas
just go do some circuits to get the oil warm.