"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."
Don’t do this…you either had a leak at your pressure gage or you blew out a gasket. All engines have blow-by or combustion gases that get by the piston rings and you will continue to build pressure until something breaks. You must let your engine crankcase “breath”. The test you wanted to do was a blow-by “flow” test. I am NOT a IO-550 expert but I would guess .5 CFM at idle and 2-3 CFM at cruise would be normal. I believe your air/oil separator inlet should be located higher than the engine fill tube vent outlet. Maybe that is causing your problem. Since the problem is intermittent, I would rule out piston rings.
Craig Berland
N7VG
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?