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.

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

1)It's a lot harder for oil to evaporate when it's contained within a
crankcase in a cool hanger. Even if it's hot out, there's quite a bit
of moisture that is suspended in the oil. There's no doubt that water
evaporates much quicker when it's hot anyway. I'd imagine you have to
let your engine sit for a very long time before the moisture becomes an
issue though. What's the longest you've let your engine sit before
sending in an oil sample?

2)Acids are deposited in the oil during combustion (the oil is not
naturally acidic). In fact, there are many additives in oil that are
designed to fight acids of combustion. Normally not a problem, because
as you say, modern oils contain acid neutralizers or some sort of pH
modifiers. But I believe many of them are much more effective at high
temps. More importantly, there is considerably more ring "blow by" at
cold temps that allows the crankcase (and oil) to be contaminated by
combusion by-products. This is why starting the motorcycle or sports
car for 5 mins at a time during the winter is a HORRIBLE thing to do.
Either leave the engine alone or use it like it's meant to be used.

3)I wouldn't think the oil is "cleaned" so much as chemically activated
during the 1+ hr warmup. This allows it to breakdown the acidic
byrpoducts of combustion (or lack of combustion, raw fuel) in the oil.

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

Well, I can believe that running "a minute or so" could be quite bad.
However, I've heard that you should just not ground-run your plane in
the winter, period, which never made sense.

This always seems counter-intuitive to me, since (as you say) the only
way internal engine parts are going to get covered with fresh oil is if
you run the engine.

Given the winters in the Midwest, there have been times when we went
three weeks without getting to fly. I've often wondered what was
worse: Letting all the oil run off the internal parts, exposing them to
corrosion, or running the engine for, say, 30 minutes at moderate RPMs
(say, 2000 RPM) to get everything good and worked up.

The only downside I can see to running the engine in this way (in the
extreme cold of winter) is that the prop can get pretty beat up on a
ground run.

> 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.

Well, I don't think it "cleans" the oil -- but it should purge the
engine of moisture. And it will certainly lubricate all the internal
parts, which is the only way I can imagine any engine making TBO.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

On 21 Apr 2006 19:43:01 -0700, wrote:

>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.

Think of it more as a mixture of water and acid and some other "crap".
I'm not sure about the 180 degrees, but it has to get *hot* to get rid
of the *stuff* and a normal ground run will not do it.

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

Although this does lubricate the parts, it does so with acid laden
oil. However the *worst* part is the cold engine oil really gets a
dose of combustion byproducts such as water, CO, CO2 and nitrides. So
rather than helping to evaporate the water and acid it has added more
and it has coated all the parts with it. Ground running the engine
will not bring up the temperatures high enough to evaporate the
contaminates, unless at high power for a prolonged time. It's
normally a whole lot safer for the engine, prop, and airplane to do
this in the air.

>
>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.

This gives the engine enough time to thoroughly warm up and stabilize
at the higher temperature. An hour at the higher temp *should*
normally evaporate any thing that will evaporate at its running
temperature. Again, the actual time of an hour is an arbitrary
number. The main point is to warm up the engine to operating temp and
keep it there long enough to get rid of the volatiles in the oil.


As a point: In the winter I wrap up the front end of the Deb in two
layers of thermal blankets and once the Tannins heater is turned on I
leave it on. The oil still is clean at 20 hours. If I only use the
heater to preheat or don't use it the oil will be completely opaque
after about five hours of engine time.


>
> 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

They come from both the engine manufacturers and oil companies who
want to see their products last.

>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

180 is a long way from boiling.

>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

The water/acid is mixed in with the oil and it takes time to
evaporate. The lower the temp the slower the process.

>that any water or moisture in the engine will be purged quickly. With

Doesn't happen. You are also wadding more water from the combustion
byproducts and the water vapor has to have some place to go. Normally
it'll just hit the cooler engine parts and condense. You end up with a
pretty warm atmosphere inside the engine with very high humidity and
the hotter the air the more water it'll hold.

>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

You'll even build up moisture at 85 degrees.

>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

It doesn't clean it, it just makes sure the contaminants that can
evaporate, do.

>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

These items come right from the oil and engine manufacturers.


Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
>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

Roger,

Thanks for your comments. I was aware of most of the typical things
that manufacturers say. I have read the articles by Shell, etc. Whereas
they give good general operating rules, I don't think they have
addressed some of the issues that I brought up. I know that I would not
give out advice for what to do when you have to let an engine sit if I
were them. It is simply not smart to do so, since it is unnecessary.
Either use it or pickle it would be my advice. I do have a question for
you however. I noticed that you have posted about the fact that you run
your preheat 24/7 in the winter on your Deb, against the manufactures
suggestion. Several engine shops say that they can tell when someone
uses preheat all the time, as it corrodes the engine. You state that
Shell is even changing their position wrt this, and that you show good
results going against convention, as I have. Do you think they might
change their mind about ground runs? Also, what temp does the Tanis
keep your oil when you run it? Popular wisdom has it that it evaporates
water out of the oil and condenses it elsewhere in the engine causing
corrosion. If the wisdom that you have to get the oil up to 180 F is
true, then how do they explain preheaters evaporating water when they
don't get to near that temp? Just another of the contradicting things
that you hear.
Another thing I disagree on is that the oil is full of acids and
other crap that will eat away the engine if you coat the parts with it.
My engine would have been corroded to hell and back if this were true,
and it wasn't corroded when I tore it down last month. Who has ever
measured the corrosive ability of such an oil? If you have info please
share it. The main thing in the oil that necessitates changing it
regularly is pure and simple carbon particles that make the oil
slightly abrasive, sort of like a mild lapping compound. That is why it
turns black. Sulfuric acid is basically clear with a slight yellow
tinge. And as for "blow by", well, a good engine has little or no
blowby. An engine that does is not long for this world. Blowby will
totally destroy the oil layer on the cylinder wall and wear the engine
at a very high rate. It is the rings, which are spring loaded, and work
about as well (probably better since the layer of oil between them and
the cylinder wall is colder and thicker) that seal the combustion
gases that will show you this. If fire from combustion is blowing by
the rings, it will be very evident upon tear down or inspection, as
they will not have the polished face that is necessary. High crankcase
pressure is an indication of this, and no aircraft engine should be
allowed to deteriorate to such a level. Blowby of the rings is not
usually tolerable for any length of time, certainly in an aircraft
engine. Once it ever starts, it usually never stops because there is no
lubrication between the ring and cylinder and the rings and cylinder
wall wear very fast and their ability to "reseal" the cylinder is lost.
Sometimes, honing the cylinder, along with new rings, will restore it,
but a ruined cylinder is highly likely. Oh, let me tell you about some
of my experiences at the racetrack on this one.
Some other points..Lycoming use to recommend and may still, that
leaning to 50 deg rich of peak was the optimum place to operate. Braly
has proven to anyone with a brain that this is the absolute worst place
to operate for optimal engine life. And his approach of using proper
test procedures and just plain doing the research is what I like to
see. Just because the factories say something, is not proof that it is
true. Remember the Mobil AV-1 fiasco?
I am envious as hell of your Deb. I would love to rebuild one or
a old Bo some day when I'm retired. Congrats for such loving care of an
old masterpice.

Blue skies,
Rusty

> wrote

> If the wisdom that you have to get the oil up to 180 F is
> true, then how do they explain preheaters evaporating water when they
> don't get to near that temp?

If you put the engine away with the oil dry (from air runs) and you keep the
engine a constant (or nearly so) cooler temp, you will not have condensation
forming inside the engine. No need to evaporate the water out, if there is
none in it.

> The main thing in the oil that necessitates changing it
> regularly is pure and simple carbon particles that make the oil
> slightly abrasive, sort of like a mild lapping compound.

False. Oil filters clean the abrasives out of the oil, if they are changed
regularly. I have heard some say, that if they can't change the oil on
time, change the filter, and more often than called for, if they can. Oil
needs to be changed because of the changes in PH, viscosity, and additives.

Diesel engines in some large boats (Navy and other commercial crafts that
are always on the move) never have the oil changed. Never. They just check
all of the oil chemestry, and put it back to where it should be (ph
especially) put some more of the additive package back in, and keep changing
filters. PH is very important.

> And as for "blow by", well, a good engine has little or no
> blowby.

It does not take much blow by to leave a lot of water and other gunk behind.
All engines have blow by. They should not have excessive blow by.
--
Jim in NC

> The main thing in the oil that necessitates changing it
> regularly is pure and simple carbon particles that make the oil
> slightly abrasive, sort of like a mild lapping compound.

I'im hardly an expert, but I've been told by our mechanic that another
thing that happens is that the carbon chains that make up the oil break.
It's still oil, but now it has shorter chains and different
properties, and eventually doesn't do very well at what it's supposed to do.

Jose
--
The price of freedom is... well... freedom.
for Email, make the obvious change in the address.

I've heard that too, and I think you are right.

Blue skies.
Rusty

"Jose" > wrote

> I'im hardly an expert, but I've been told by our mechanic that another
> thing that happens is that the carbon chains that make up the oil break.
> It's still oil, but now it has shorter chains and different properties,
> and eventually doesn't do very well at what it's supposed to do.

True, but I think the shorter chains also evaporate more readily. There
must be some way to deal with that, because I know that some large engines
never have their oil changed. It blows my mind.
--
Jim in NC

"Morgans" > wrote in message
...
> True, but I think the shorter chains also evaporate more readily. There
> must be some way to deal with that, because I know that some large engines
> never have their oil changed. It blows my mind.

Some large engines burn and leak oil fast enough that you are essentially
changing the oil every time you fly.