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 a

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