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From: "Christopher Zavatson" <Christopher.Zavatson@udlp.com>
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Subject: [LML] Re: Low oil temps on 320
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edechazal@comcast.net writes:
<<But I wonder what the oil temp really is.  Seems to me it is
different
temperatures throughout the circuit.  Very hot before the cooler, less
hot
after the cooler, etc. I understand the thermistor (?) doesn't open
until 180
degrees.  The oil must be going to the cooler since there is no
significant
cooling mechanism besides the cooler.  Therefore, the oil must be at
least 180
degrees up stream of the cooler.  I'm not sure where we have the temp
sensors
located. >>

Oil temperature specs are for Inlet Oil Temperature (see Lycoming
Operator's Manual).  That means into the engine oil circuit.  Your oil
temperature probe must measure the oil after it has gone through the
cooler and before it enters the oil galleys.  Oil in the sump and
through the oil pump will be at a higher temperature.  A minimum
temperature of 140 deg F is specified for continuous operation.

When cold, the vernatherm is actually open.  The oil can go through the
engine or the oil cooler.  Since the cooler is more restrictive, the
engine wins.  As the oil heats up the vernatherm it begins to close off
the direct path to the oil galley and more of the oil is forced through
the cooler.  At full extension, all oil is flowing through the cooler. 
I'm puzzled by engines that run with low oil temps.  It would seem the
flow balance between the cooler route and the rest of the oil circuit is
mismatched or the vernatherm is forcing too much oil to the cooler right
from the start.  My first hand experience is limited to two different
360's.  Both operated with a minimum oil temperature of 180 degF even if
the OAT was 0 degF.
Perhaps some of the engine gurus have more insight into this.
Chris Zavatson
N91CZ
360 std