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Oil
Levels and Consumption
OIL LEVELS: As long as I have
been flying aircraft I have heard from nearly every person I have come in
contact, 'I don't fly her full on oil as she just blows out that first quart",
or, "all aircraft find their comfort level of oil and they just seem to stay
there". THIS IS ALL BULLSHIT! The fact of the matter is, those who say this
don't have a clue as to the oil burn rate of their aircraft. If you want to lose
a quick $500, bring your aircraft to me, lets fly it for 10-hours and I will
prove it to you; but I will not fly it more than a quart low on oil.
First, one must understand that oil is not just a lubricant. Oil has a secondary
purpose which you should be learning in your flight training; oil provides
internal cooling. That is, oil absorbs heat generated inside the engine and
transfers this heat in the oil cooler (heat exchanger). Less oil means less heat
absorption/transfer capabilities and consequently a hotter internal temperature.
As the internal temperature rises, oil consumption increases. Why? As the
temperature of the oil rises, it becomes thinner; thinner oil means smaller
drops; smaller drops leak faster than larger drops. This means that the thinner
oil will leak past the rings and valve guides into the combustion chambers at a
higher rate as well.
Leak Rate: Each quart of a given oil contains a given number of drops. If a leak
develops, the leak will occur at a 'rate' or drops per second or minute. If you
make a habit of running your engine low on oil, you will decrease the time your
engine will live if a leak develops. I was flying a Bell 47 with a Lycoming 435
several years ago when it developed an oil leak at the engine filter container.
I had flown for 2-hours when I landed at an airport for fuel. Oil was
everywhere. I landed with roughly 6-quarts remaining in a 12-quart system. Had I
the habit of filling the oil only partially as often occurs, this engine would
almost surely have failed as the critical level of oil would have been reached.
The critical level is that where although there is some oil in the engine, it
may be in lines, the heat exchanger, etc., with minimal oil in the crankcase to
transfer heat and to lubricate; at this point, the engine will overheat
internally and bearing, metal fatigue, and other internal damage will occur.
I will not drive my car low on oil and I can coast it to the side of the road.
Why would I fly an aircraft low on oil where if an engine problem develops, I
have an emergency?
Engine manufactures do not put the 'Full level' on the indicator for their
health. They do it because they know what the engine oil requirements are. They
also do not indicate the 'minimum low level' so that foolish pilots can run the
aircraft at this level for extended durations. The minimum low level is the
critical level where heat transfer and burn rate reach a 'critical level'.
I don't care what your instructor is telling you, keep your aircraft full of oil
(add 1-quart as soon as it indicates 1-quart low). If your instructor or the
school you are attending don't want to keep it full, then you need to refuse to
fly. They need your money so the oil will be added.
Fly safe!!
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