M20 Air/Oil separator

Don't take my word for it! Try flying your airplane full and then at
whatever the oil level stabilizes at. If the oil didn't contact the crank,
then it wouldn't be expelled out the breather (on a healthy engine). The
oil may not contact the crank in level, smooth, unaccelerated flight but it
does under acceleration, climb and descent.

Mike
MU-2


"Matt Whiting" wrote in message
...
Mike Rapoport wrote:

You are not getting it. How much hotter do you think the case is 1"
above
the oil level? About the same. The important part of this is that you
are
adding more heat by raising the oil level because the crank is thrashing
about in the oil. That is why the oil is vented overboard when you
fill
the case. Try different oil levels in your airplane and see for
yourself.
You probably won't be able to measure the difference unless you have a
digital oil temp guage. It also take power to thrash that crank through
the
oil, power that would go into turning your prop otherwise. This whole
issue
is one reason why race cars use dry sump lubrication systems.

No, you're not getting it. If the oil is hotter than the case, then it
will lose heat through the case. If it is losing heat through the case,
then being in contact with more case area will result in more heat
transfer.

I honestly don't know if the oil contacts the crank in a typical Lyc or
Conti. It may, it may not. I'd be very surprised if it does, because
most engines with pressure lubrication systems tend to fail very quickly
when any substantial amount of oil in the sump contacts the crank. That
is why overfilling a crank is so strongly warned against by almost all
engine makers.


Matt