Probably, but there might be more than one condition working
on the oil loss. I'd look at quantity and baffling as well
as crankcase pressure, but oil does strange things. There
are dry sump engines that scavenge oil from the crankcase
and return it to an external oil tank, these have two oil
pumps, on to provide engine pressure and the other [larger
pump] to remove the used and foamy oil from the engine. In
all engines [modern designs] the oil that was sent to the
rockers must be drained away back to the crankcase. If
there is a blockage, it will pool and be more likely to be
sucked past the valves.

It is possible that the oil level seems to stabilize at 5.5
quarts only because the flight was terminated and the oil
replenished.

A sudden change in the pattern is what should cause alarm
and investigation. If the airplane has a history of doing
one thing and then that changes for no apparent reason, why
is important to find out.


--
James H. Macklin
ATP,CFI,A&P

"soxinbox" wrote in message
...
| Excuse my ignorance, but how would valve guides, bad
rings, etc cause it to
| leak down to 5.5 quarts and then stop. It seems these
causes would result in
| a continued loss as long as the engine was run.
|
| "Jim Macklin" wrote
in message
| news:kaStg.67770$ZW3.1299@dukeread04...
| Do a differential compression test and pay attention to
| valve guides play and seals, often the oil is not being
| blown out the breather, but is leaking around the valves
| [even one valve] and burning. If you have high leakage
| during the differential compression test, you're getting
too
| much blow-by and that is raising the crankcase pressure
and
| blowing oil out the breather tube. If the breather is
| blocked, it will blow the main seal and you'll see oil
| behind the prop. If the oil level goes down fast and
then
| stabilizes, you may have a dipstick that is not
calibrated
| properly and you're over filling.
|
| The engine is old, nearly ten years, check all the seals
and
| mating surfaces. You only have 900 hours, but that is
less
| than 100 hours a year. Corrosion in the cylinders and
blow
| by, and oil being sucked past the ring into the
combustion
| chamber are all possible, Check valve guides and seals,
| differential compression and if available, borescope it.
| Higher oil pressure would increase the leakage, but not
| effect the valve guides or rings. An oil separator will
| only help if the oil is going out the breather tube.
|
|
| --
| James H. Macklin
| ATP,CFI,A&P
|
|
|
| "Robert M. Gary" wrote in message
|
ups.com...
| |I have an IO-360-A3B6 900 SFNEW in '97. I used to be
able
| to keep about
| | 7 quarts in it without it blowing out. Now it seems to
be
| blowing oil
| | down to about 5.5 quarts. Since I live in the 100F
OATs
| part of the
| | country, the extra oil really helps cooling.
| | Should I worry about what is causing the extra oil
blow
| out or just
| | chock it up to an aging engine. I know some engines
always
| blow out to
| | 6ish quarts.
| | If I shouldn't worry about the extra blow out I'll
just
| put a separator
| | on it, but I don't want to mask a problem first. One
| recent change is
| | we raised the oil pressure since the regulator had
been
| slipping prior
| | to annual.
| |
| | -Robert
| |
|
|
|
|