Is is possible that it just takes a lot longer for the oil to exit the
breather tube in cold weather because it is thicker due to the lower
temperatures?

Mike
MU-2


"Jim Burns" wrote in message
...
Why would a cold engine drip oil out of the breather? If you're bored or
have any answers... read on.

Lycoming IO-540 C4B5

Like some of the other owners in the group, we've had a mystery oil leak
on
one of our engines. Nothing severe, not enough to show up as "missing" on
the dip stick. Primarily just a nuisance.

Last week ours took on a new characteristic that I can't figure out, so
I'll
throw a few details at the group to see what tid bits of knowledge,
experience, and plain ole guessing can be generated.

Original leak seemed to be coming from around an oil return hose on our #3
cylinder. Nearly impossible to get my hands on with the bottom cowl in
place, I tightened it up as much as I could without replacing the hose
clamp. Occasionally notice a drop of oil hanging from the bottom of the
inboard end of the hose.

Oil accumulates along the back side of the fuel injector throttle body in
a
valley where the throttle body moves upward to connect to the air intake
scat tube.

Small amounts of oil are obviously flying around inside the cowl as single
drops can be found on the bottom of collection points such as bolt heads
and
flanges. The floor of the bottom cowl never has any streaks, streams, or
oil lines but is generally covered with a very thin coat of oil that
returns
even after washing and wiping it down.

The above observations were constant all summer when using Aeroshell W100.
Never displacing an amount that was observable as a loss on the dipstick.
Normally both engines use about a quart of oil every 6-8 hours if we fill
them up to 12 quarts. If we leave them down around 10 quarts, they can go
up 10 hours before needing to add a quart.

Ok, new observations and clues.
As winter approached we changed oil and filters and switched from W100 to
15W-50. We've flown about 10 hours on this oil change so far, but this is
what I've noticed.

A puddle of oil, I'd say about 2 tablespoons full, appeared on the floor
directly under the breather tube the day AFTER as short 30 minute flight.
The plane came out of a heated hanger and was completely warm and toasty,
I
flew it home, tucked it away, no drips or drops as I left our old unheated
hanger. The NEXT evening I went up to the hanger and the puddle was
discovered. I wiped it up, opened the cowls, looked around and everything
seemed as described above (a few drops hanging here and there, oil along
the
backside of the throttle body ect.)

The following night, I needed to shovel the snow away from the hanger
door,
so I went in and there it was AGAIN! The plane hadn't moved, hadn't
flown,
engines not started, but it dripped another 2 tablespoons full of oil out
of
the breather tube and onto the floor.

The oil I wiped up off the floor is usually darker colored than the oil on
the dipstick.

So here's what's got me puzzled.... why would a cold engine drip oil out
of
the breather? Especially the day AFTER it was flown? I can understand if
there was pressure remaining in the sump there may be some spit out the
breather, but after 24 hours, I can't believe there would be any pressure
in
the sump.

Second thought, which I've been told Lycoming's don't have a problem with,
would be a leaking intake valve guide. Could that be seeping oil back
down
through the intake and somehow make it to the throttle body? One of the
breather lines goes to the back side of the throttle body and then (I
assume, can't see it) enters the sump. The other breather line goes up
towards the back of the accessory case, towards the oil pump I believe, I
need to investigate this line more, I couldn't see very well.

Any ideas?

Thanks!
Jim