| Dan, I had the same issue (and almost exact setup it sounds like). My Legacy has a 10:1 from Barrett, the Aerochia 12(+) quart pan, and breather into the exhaust. I had no separator, and I have cowl flaps.
At lower altitudes during break-in (8k and below), all was fine. Then, at about 75hrs I did my first flight up high (17,500). After 2.5hrs, I landed and was shocked to have to add 3+qts (the engine had been using nominal amounts of oil down low). I took off again, straight up to 17,500. After about 3hrs at 17,500, my low oil level light illuminated (I have a level sensor). I diverted and found that I had lost 4+qts over those 3hrs.
I measured the pressure in my breather tube also, and got ~+2" H2O with the cowl flaps closed. So, I moved the breather exit to the cowl exit area from the exhaust. I also added an Andair air/oil separator and catch can (to keep oil off the belly.
Fred Moreno and others, much more educated than myself in the the area, have some theories about pressure differentials and engine design, but thankfully this seems to have solved the problem for me.
Clark
Legacy, 130hrs TT On Mon, Nov 5, 2012 at 4:39 PM, Dan Ballin <dballin@gmail.com> wrote:
I am flying a Lancair Legacy with an IO-550 10:1 compression -
Performance engine that has been inspected and rebuilt about 60 hrs
ago. I have had a problem, which I attributed to new cylinder/rings,
with excessive oil consumption. Initially I was using about a qt an
hour and this improved at about 15 hrs. Seemed like normal break in.
Then one flight back from the coast of OR (Sea Level - I fly out of
Bend - 3500 ft), I started losing oil pressure. When I landed after
the hour flight I had about 5 qts left. I started with 9. I
attributed it to a crazy idea I had to hook the breather tube into the
exhaust. I was getting really tired of cleaning the bottom of the
plane and my hangar floor. I disconnected it and flew and problem
solved. Just recently on a trip back East the same thing happened.
Got to Rawlings, Wy 8.5 qts running grat no problems. Next stop about
1.5 hrs, 2 added qts. On my way to Kansas City oil pressure dropping
slowly so I diverted and now I was down to 4-5 qts. After spending
the night in Kansas city and buying a case of oil, I flew back to
Bend. Used 1/2 qt in 6 hrs.
So a few things. I have a 12 qt oil pan, I have an air/oil separator,
I checked my crank pressure by hooking a pressure gauge to the
breather (before the separator) and it is high somewhere in the 4-5
psi. I did a compression check and.
OK so why intermittently dumping from the oil breather?
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