Sender: "Marvin Kaye" <marv@lancaironline.net>
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Date: Sat, 02 Apr 2005 09:34:26 -0500
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From: "Gary Casey" <glcasey@adelphia.net>
Subject: Re:  Oil viscosity
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I previously posted:

<<I don't think oiling the engine is a problem
and if the viscosity of the oil is low enough to allow the engine to start
and run it is probably good to go by the time you taxi out and do the runup.
And I don't think there is a problem with mixing viscosities or brands.>>

Jeff replied:

<<Lot's of assumptions here. Your butt is on the line. Where's the data?>>

As I specified, it was just my opinion - I had no data available.  As for
over-pressuring the oil filter, there is usually a red-line oil pressure
(certified aircraft) and as long as the oil pressure limit is not exceeded
(does everyone look at oil pressure during runup and the takeoff roll?)
there shouldn't be a problem with that.  As for hurting the engine, the last
two Cessnas I owned stated that takeoff was okay as soon as the engine would
"accept throttle."  Since they didn't include the data in the POH, that
might also be just their opinion.  Aircraft engines have such a large
displacement, small starter and battery and high oil viscosity (compared to
cars) that really high oil viscosity will essentially prevent the engine
from cranking and starting.  Another anecdote:  Standby generating systems
using large diesel engines always start and immediately run at rated rpm and
full load, regardless of the initial temperature and the engines are
typically the same ones as used for all other applications.  Doesn't seem to
bother them.  As for mixing brands and viscosities, it has been "accepted
practice" to do that for maybe 50 years - oops, I don't have the data to
show that ALL brands can be mixed with ANY brand of oil.

One can always err on the conservative side and take the time to warm the
oil, avoid shock cooling, run only one brand and type of oil, etc and it
will usually at least do no harm.  Once I was riding with a friend on short
final at OSH.  We kept getting closer to the Mooney ahead of us and when I
could count the rivets on the tail I asked him if it wouldn't be a good idea
to slow down - he replied that he was trying to avoid "shock-cooling the
engine."  One has to keep one's priorities straight.   As for me I worry
more about fouling the plugs from long ground operation than damage to the
engine due to cold oil.  It's a tradeoff.

Gary Casey