Lubrication and Rust Prevention -- It Does Two Big Jobs
by Tim Kern
It's always daunting, when we
journalists run into someone so much smarter than ourselves, that
we can't even pretend to belong in the same room with him. It's
even better, when we get invited in. Such was the case at Sun 'n
Fun, when Exxon Mobil Aviation Lubricants Product Advisor, Shlomo
Antika, sat down with us, to give some insight into what aviation
oil becomes, once it's in our engines.
Dr. Antika (he's a PhD. Chemical Engineer) started with some
basics: without proper lubrication and rust protection, our engines
rust out, or wear out. Although the two conditions are obviously
related at times, the challenges for our oil are quite
"You have to have oil," he said, starting slowly. "You need the
proper mechanical conditions, and a proper filter. The oil has to
be of the right viscosity; and it has to be the right type of oil.
Nowadays, that usually means a dispersant type."
In older engines, he explained, mineral
oil (non-dispersant) may still be what you want. "You're looking at
20~25 hour oil changes," he noted, "and you're probably losing or
burning a fair amount [of oil], so it's really not too bad,
internally [inside the engine]." One other fact of life comes into
play: "Some engines are so old, they depend on deposits to keep
from leaking." If that's your engine, keep the oil clean and change
it often. You can go to a dispersant oil at your next rebuild.
"All oils," Dr. Shlomo said,
"require a basic level of filtration -- you have to remove the
dirt, contaminants, and byproducts of fuel degradation." Gas in the
oil is a multi-faceted problem: it thins the oil, and it can create
a more-combustible environment inside the engine.
"The only way to get gas out of the oil," Dr. Antika noted, "is
to run it out, or, of course, change the oil. This is not a
His job, on the 'lubrication' side, sounds simple: "What oil
engineers do is create molecules that get between the moving metal
Moisture, bad; lubrication, good.
"You must protect your engine
against wear and rust. Both take place on steel surfaces; wear
occurs on any potentially rubbing surface."
"Wear additives," he continued, "protect the moving parts with a
molecular layer [of lubricant and metal surface strengthened by
reaction with antiwear additive] between them."
Lube requirements: thin enough, thick enough, slick enough,
Oil has to be thin enough to flow,
at the lowest temperature your engine encounters. That's at
startup; and the temperature is dictated by the environment. A
low-viscosity oil (a 5W, for instance) will flow better at lower
temps than a higher-vis (40) will. A multi-viscosity oil, like a
20W-50, will flow like a 20W at low temps.
"At low temperatures," our host said, "the oil must be able to
flow. Some engines are so tight mechanically, that's a real
challenge. There is 'no' mechanical room for the oil to flow --
another reason to do a careful warmup."
At high temperatures, there's another set of problems. They
relate to the lubrication properties. Will the oil's molecular
structure break down and allow metal-to-metal contact? "Is the
viscosity sufficiently high to protect the parts? You have to
maintain a lubrication layer. This layer -- it may be only 20
microns -- but it has to be there," said the engineer. "You don't
want metal to touch metal." As temperatures go up, the lubrication
problem becomes greater. "If you use even a 40-grade oil in a hot
engine on a hot summer day, you may not have sufficient
Rust is often the bigger enemy of your engine.
"Rust prevention," the good doctor
said, "is 'formulation science,' a pseudo-science,' really." That
means there are elements of art and experience, and plain old
trial-and-error involved. There is a popular misconception, that
'rust' and 'corrosion' are pretty much the same thing,
differentiated only by the metals involved. For the purposes of our
understanding, that's not so. "Corrosion is a chemical attack on
the metal, due to additive or oil degradation. It's typically seen
in higher temperatures. Water is not part of this phenomenon," Dr
Antika explained. "Rust, on the other hand, involves water on
ferrous metals. Technically, you're talking about 'galvanic
corrosion,' a battery formed in the presence of water on iron."
"Any oil, even mineral oil," Dr Antika said, "will give you some
rust protection. In a formulated oil, you also have chemistry on
your side, as well as the physics of the oil."
Two kinds of water?
"There are two kinds of moisture we talk
about in oil," he told us. "There's 'dissolved water,' and
'suspended water.'" The only way to get rid of the
dissolved water is to change the oil -- but the amount of dissolved
water, as a proportion of the moisture in your engine, is
miniscule, and really not in the same league as suspended water, as
a trouble-maker. Address the suspended water, and let the dissolved
water take care of itself.
"Suspended water," he continued, "is bad. It sits on metal
surfaces. We design additives to keep the suspended water off the
metal." Here's how: "'the polar heads' tend to accumulate on the
metal surface, the (oily) tails repel the water."
Here's how it works: "Oil picks up
pollutants during operation and when it sits. As an engine runs, it
produces byproducts of combustion and wear -- the filter handles
those." Water is the bigger problem: "Water -- especially if you
fly infrequently and/or in a humid environment -- you accumulate
water, and you often don't get enough 'high-temp time' to get rid
of it." Suspended water will boil (surprise!) at water's boiling
point. "You have to exceed that temperature for some time," Shlomo
explained, "and there has to be an area through which the water can
escape. Some water condenses and returns: that's why the time of
high-temperature operation is important."
How hot is 'hot enough?'
"If your oil temperature gauge says
190F," he picked a typical example, "it's likely the working
surfaces are 220, 230 -- it's at those surfaces where water will
flash off. If you run long enough, hot enough, you'll get rid of
the suspended water. That's the best you can do."
"At even 220~250 degrees, oil degradation is not really a
concern, if you're using a properly-formulated oil, for 100, maybe
200 hours. Higher temperatures, of course, accelerate the
process..." Change your oil: "You change oil at 50, 100 hours -- an
internal combustion engine is rough on oil; it produces a lot of
What about oil heaters?
If 'hot' is good, is a heater better? Like
everything else a good doctor will prescribe, moderation is the
key. "People use oil heaters to help with the flow at startup.
That's fine," said our mentor. "But when you leave the heater on
all the time, you'll be percolating the oil in the pan. Oil will
drain off the static surfaces -- yet you're still percolating the
water in the oil in the pan," he warned. "That water will condense
on the exposed surfaces; and much of it will just return to the pan
-- but the rest will stay on those exposed surfaces." Without a way
to escape, the water just stays in the engine -- but now, the
temperatures are higher, and the chemical reactions are thereby
accelerated. "Additives will help maintain a barrier to the water,"
he said, but why stress them more than you have to?
As far as it goes, a heater can
be a good idea, Dr. Antika said, but "Turn it on a couple hours
before flight; don't leave it on all the time, or even overnight."
[It depends on the heater, of course. The Tanis system heats the
whole firewall-forward area, and avoids these typical problems.
Turn the Tanis on all night; it'll work --ed.]
- Whenever possible, use a high-quality, dispersant oil
- Make sure the viscosity range is proper for your flying and
- Use a pre-heater, but sparingly
- Fly long and often [great idea, eh?]
- Employ a quality filter
- Have your oil analyzed, or at least cut open the old filter and
have a look
- Change both oil and filter frequently -- both are cheaper than
- If you're not going to be flying for a while -- change the oil
and filter, run it for a few minutes, then park it.
[This article is the second in a series (here's the FIRST) of regular ANN
features, wherein we periodically bring you tips and advice
from professionals in the field, of interest to our readers. We'd
like to know what you think of this format, and this idea -- and
this article. Excuse us, now -- we've gotta get out to the
[Thanks to Exxon and Tanair for the photos --ed.]