1. I'm a bit of a skeptic on "ring flutter", but the piston ring requires some pressure against the bore and the ring land to maintain a seal. Under some conditions of low manifold pressure it could come "unloaded" and allow significant oil to pass. But remember that for half the time there is virtually no pressure in the
cylinder, so how does one explain that? However, the subject of ring sealing is complex and there could be a condition of pressure and speed under which the ring loses its ability to control oil flow, so whether you call it flutter or something else, it can be real. Continental went to a lot of work to develop the iron piston liner
and I'm sure that helps keep a consistent piston ring environment. If the ring don't seall really well, if the manifold pessure is reduced significantly below atmospheric the low pressure could draw significant oil into the engine. This would be during descent or on the ground. But that doesn't sound like it is the issue in this case.
2. Air/oil separators are a bit of a mystery to me. I worry about the drain line because there is so little elevation to drain the oil. Note that the separator is only a few inches above the engine oil level. What happens if the crankcase pressure is just a little higher than the pressure in the separator? That could happen if there were even a little restriction between the engine and separator - there would be a pressure drop between the crankcase and separator volume. And what if the drain line is below the oil level - or maybe at a
location that gets a lot of oil splash? Then the engine will pump oil OUT the drain line, filling the separator, and pump oil overboard. I wonder if that isn't the issue. Even if there are 10 inches of elevation in the drain line it would take only 7 inches water pressure to pump oil up 10 inches.
3. I think the post mentioning crankcase pressure of 5 psi must have meant 5 inches of water(1 psi is equivalent to about 12 inches of water). 5 psi is really high and if true indicates a serious problem or a restriction in the breather system.
4. I'm skeptical of the breather outlet condition (into the exhaust or other details of location) being a significant factor. For instance, a reduction in pressure at the outlet can't "suck" oil out of the crankcase. At least I can't think of a way that could happen.
Just a few thoughts - I'm interested to read about
the outcome of this thread.
Gary Casey
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?