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

wrote in message
...
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.

Which is a closed loop. So how does the moisture escape?


--
Jim Pennino

Remove .spam.sux to reply.

"mikem" wrote in message
ups.com...
Crankcase fumes are sucked into the induction manifold (and burned by
passing through the engine) via the Postive CrankCase Ventilation check
valve.

The question still remains....how does the moisture escape as modern engines
are not vented to the atmosphere but are a closed loop. We aren't talking
about crankcase fumes but about moisture supposedly being boiled off into
the atmosphere.

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

What proof is there that it is bad? And sometimes weather and
circumstances don't allow people to fly. I believe that ground running
is better than bare metal corroding. My engine would have been corroded
a long time ago if the oil from a ground run would do that, and it
hasn't been.

Blue skies,
Rusty

But its not a closed loop. An auto engine operates at temperatures up
to 235 degF because of the pressurized cooling system. Water in the oil
boils and steam escapes from the oil. The PCV system effectively sucks
the moisture laden air, steam, and oil droplet mist in the crankcase
into the intake manifold. It gets mixed with other air that came
through the air cleaner and fuel, gets compressed in the cylinders,
goes bang, and 95% of it goes out the exhaust pipe. Only a tiny
fraction leaks back into the crankcase as a result of blowby...

The process reaches an equilibrium with very little residual water in
the oil. When the engine is stopped and cools, that is when the water
content of the oil is the lowest.

I think that several people have tried to make this clear. The oil warms up
and water evaporates out into the crankcase. the PCV valve allows the water
vapors to be sucked from the crankcase into the intake manifold. It is mixed
with the intake air goes through the cylinder and pumped out the exhaust. It
is not a closed system since the vapors are free to exit the motor via the
exhaust ( while running ).

"Dave Stadt" wrote in message
news

"mikem" wrote in message
ups.com...
Crankcase fumes are sucked into the induction manifold (and burned by
passing through the engine) via the Postive CrankCase Ventilation check
valve.

The question still remains....how does the moisture escape as modern
engines are not vented to the atmosphere but are a closed loop. We aren't
talking about crankcase fumes but about moisture supposedly being boiled
off into the atmosphere.

Well stated. The temperature of the oil is measured at only one place. The
temperature of the oil varies greatly within the engine. It is probably
hottest when it leaks off the cylinders. It is coolest exiting the oil
cooler. A reading of 180 or 160 might mean that oil is above the boiling
point at many points inside the engine. Also with the oil being atomized by
the slinging in the crankcase, water will evaporate at a good rate while
below the boiling point. I would love to see some scientific data on the
evaporation rate vs. oil temp.


"M" wrote in message
oups.com...

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.

"Dave Stadt" wrote in message
news

"mikem" wrote in message
ups.com...
Crankcase fumes are sucked into the induction manifold (and burned by
passing through the engine) via the Postive CrankCase Ventilation check
valve.

The question still remains....how does the moisture escape as modern
engines are not vented to the atmosphere but are a closed loop. We aren't
talking about crankcase fumes but about moisture supposedly being boiled
off into the atmosphere.

'Modern' engines (with PCV for POSITIVE Crankcase Ventilation) are NOT a
closed loop. The atmosphere from the crankcase is sucked into the intake
manifold by engine vacuum (then burned in the engine), the atmosphere sucked
out of the crankcase is replaced by filtered air (either from a breather or
engine intake air filter) and blowby gases. Usually an attempt is made to
induce some cross flow such as by sucking air out of one end (or side) of an
engine and replacing it in the other. This ventilation is maximum at closed
throttle (low manifold pressure) and minimum at full throttle (high manifold
pressure).

AFAIK most aircraft use the older type of crankcase ventilation system
utilizing (what in an automobile was called a road draft tube) a tube cut at
an angle and extended into the airstream to create a lowered pressure. This
system only functions when the tube is in moving air, and on the ground this
is only supplied by the prop wash and is significantly less than the flow
occurring when actually flying. This is also part of the reason that
actually flying is far superior to ground running for removing moisture from
the crankcase.

Happy landings,

soxinbox wrote
Also with the oil being atomized by
the slinging in the crankcase, water will evaporate at a good rate while
below the boiling point.

Bravo Sir! Brilliant! Even at 1500 rpm, there is a hurricane of wind
in the crankcase that would make Katrina seem like a Summer breeze. And
at 60-90 psi of oil pressure, the oil is being pumped through the
engine like a firehose. Who said it is just sitting in the bottom of
the pan?

I would love to see some scientific data on the
evaporation rate vs. oil temp.

So would I!

Rusty

Mikem,

You make some good points. The main issue I have is simply whether it
is better to run the engine and oil the parts, or just let it sit.
Someone posted that where they live, that many times flying is not an
option for weeks at a time. I completely agree that flying for an hour
or so weekly is the best thing, but I have had times during the winter
when short days and drizzly crappy weekends have made getting in the
air dangerous when my schedule has allowed it. I know what the effect
of moist air against bare metal does. What does the coat of oil from a
ground run do to the metal? I seriously doubt if it is as bad. I would
like to know if anyone has actually measured the acidity or moisture
content of the oil in such an instance? As I stated, my oil analysis
always shows no moisture; none! And I ground run the engine alot.
Glad to hear your comment about the exhaust system issue. I
wouldn't be surprised if the advice about not running the engine up to
temp on a car for this reason, was the beginning of the advice not to
do the same for airplanes. I wonder what it does for our mufflers given
they are designed differently. Those puppies get hot quick!
It would be a shame to trash an engine trying to save an exhaust! .

Rusty

"Dave Stadt" writes:


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

The question still remains....how does the moisture escape as modern engines
are not vented to the atmosphere but are a closed loop. We aren't talking
about crankcase fumes but about moisture supposedly being boiled off into
the atmosphere.

They most surely are vented. They have an air intake & an exhaust
pipe. The PCV system sucks any *crankcase* fumes into the intake
so as to burn them in the combustion cycle. So as the oil gets hot
and boils the water vapor out, it gets sucked into the intake side...

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