Jay Honeck wrote:
Atlas just got his oil/air separator installed today. (For those who may
not know, Atlas is our '74 Cherokee Pathfinder, so-named because he can lift
literally anything we can fit inside!)
snip
Anyone else got one of these things? Are there any "gotchas" to watch out
for, or are they as bullet-proof as they seem?

Hi Jay,

A few comments.

Air/Oil Separators do seem to perform their intended function with a
minimum of problems (when installed correctly, anyway), but my mechanic
recommended I NOT install one because they return moisture to the case
that would normally be vented overboard with the oil vapor. The
long-term effect is reportedly the same as if you were to run the engine
for short periods without attaining the operating temperature required
to boil off the water -- namely, corrosion.

There is also something to be said, IMHO, for adding oil between oil
changes. Oil breaks down over time, and throwing in a quart every 5-10
hours replenishes the anti-wear/anti-corrosion additives as well as
increases the oil's natural ability to hold contaminants in suspension.

Also, I have found no hard evidence that keeping the oil topped vs. 1 or
2 quarts down provides any additional cooling or anti-wear properties.
If we keep our 172's O-360 between 6 and 7 quarts (max 8), our belly
remains reasonably clean and it runs at what I'd call "nominal"
temperature.

This is no surprise, really, as the O-360 certainly doesn't *need* six
or eight quarts of oil. I know of one application (the Seminole) in
which it is certified to run on as little as 2 quarts. I'm sure other
Lycoming engines such as your O-540 are the same in this regard. As
long as you maintain the minimum required oil level, a couple quarts
down isn't going to make any difference except on a LONG ferry flight
where you can't add oil in flight. Most POH's seem to reflect this
(e.g. "Top off for extended flight").

Lastly, FWIW, my partner's other airplane (a 182) has a M20 installed.
Yes, its belly is largely free of oil residue, but it still seems to
acquire a dry, chaulky residue in any case. It looks and feels like
something you'd find just aft of an exhaust stack, and may very well
result from the exhaust...I don't know for sure. But, I do know that
the belly is still dirty enough after 50 hours that I have an
overwhelming desire to break out the creeper and WD40, so I'm convinced
an oil separator would save me no labor. :-)

Safe flying,

-Doug

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Doug Vetter, CFIMEIA

http://www.dvcfi.com
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