Missing oil?

I'm posting on behalf of my father. My father has been flying a friend's
older 172. The 172 was recently flown on a 8-hour round trip. During this
trip, the plan burned 3-quarts of oil. On return, a compression check was
performed. All came back with 75's or better. A check for
leaks did discover two *very minor* leaks but nothing which would account
for 3-quarts in 8-hours.

The engine bay was not covered with oil and no pools of oil were found.
There is not a large streak of oil on the bottom on the plane as one would
expect if it were simply leaking.

All this makes us think that the plane really is burning the oil but
wouldn't the compression check yeild much lower results if it were burning
that amount oil? Where's the likely suspect here?

Thanks in advance,

Greg

I would look again at the belly to see how badly misted it is with oil. It
might be getting pulled out the crankcase ventilation tube. The geometry of
the tube is important in preventing too much oil being dumped overboard.

I would also pull the spark plugs and check for oily plugs. Some oil on the
bottom plugs is not too unusual, but oil on the top plugs is reason to
worry.


"Greg Copeland" wrote in message
news
I'm posting on behalf of my father. My father has been flying a friend's
older 172. The 172 was recently flown on a 8-hour round trip. During this
trip, the plan burned 3-quarts of oil. On return, a compression check was
performed. All came back with 75's or better. A check for
leaks did discover two *very minor* leaks but nothing which would account
for 3-quarts in 8-hours.

The engine bay was not covered with oil and no pools of oil were found.
There is not a large streak of oil on the bottom on the plane as one would
expect if it were simply leaking.

All this makes us think that the plane really is burning the oil but
wouldn't the compression check yeild much lower results if it were burning
that amount oil? Where's the likely suspect here?

Thanks in advance,

Greg

In article ,
Greg Copeland wrote:

I'm posting on behalf of my father. My father has been flying a friend's
older 172. The 172 was recently flown on a 8-hour round trip. During this
trip, the plan burned 3-quarts of oil. On return, a compression check was
performed. All came back with 75's or better. A check for
leaks did discover two *very minor* leaks but nothing which would account
for 3-quarts in 8-hours.

The engine bay was not covered with oil and no pools of oil were found.
There is not a large streak of oil on the bottom on the plane as one would
expect if it were simply leaking.

All this makes us think that the plane really is burning the oil but
wouldn't the compression check yeild much lower results if it were burning
that amount oil? Where's the likely suspect here?

Thanks in advance,

Greg

Did he fill it up to the "full" capacity? If so, he could be blowing it
out until the oil level reaches a "normal" operating level, usually
about 3 qt. short of "full."

How far from TBO is the engine? The compression test would just test
the valves and the comnpression rings are sealing. If the oil control
rings are weak you could be getting excessive oil up to the combustion
chamber and a compression test would not show that. Check the spark
plugs for oil. Lower plugs with some oil is cool, uppers with oil
uncool...

Also check the crankcase ventilation system. It doesn't take too much
pressure to blow oil out of the tube.

Jon Kraus
'79 Mooney 201

Greg Copeland wrote:
I'm posting on behalf of my father. My father has been flying a friend's
older 172. The 172 was recently flown on a 8-hour round trip. During this
trip, the plan burned 3-quarts of oil. On return, a compression check was
performed. All came back with 75's or better. A check for
leaks did discover two *very minor* leaks but nothing which would account
for 3-quarts in 8-hours.

The engine bay was not covered with oil and no pools of oil were found.
There is not a large streak of oil on the bottom on the plane as one would
expect if it were simply leaking.

All this makes us think that the plane really is burning the oil but
wouldn't the compression check yeild much lower results if it were burning
that amount oil? Where's the likely suspect here?

Thanks in advance,

Greg

All this makes us think that the plane really is burning the oil but
wouldn't the compression check yeild much lower results if it were burning
that amount oil? Where's the likely suspect here?

Could be worn valve guides. They won't show up on a compression
check, but oil can be sucked in around the intake guide when the valve
is open.

Don

You are corect... For that matter worn valve seals too...

Jon Kraus
'79 Mooney 201

Don Hammer wrote:

All this makes us think that the plane really is burning the oil but
wouldn't the compression check yeild much lower results if it were burning
that amount oil? Where's the likely suspect here?


Could be worn valve guides. They won't show up on a compression
check, but oil can be sucked in around the intake guide when the valve
is open.

Don

Check and see that the slit in the oil drain tube
is not plogged up inside the cowled area. If the slit is
plugged with old oil gunk, the tube will suck oil overboard
and since they stick out a bit into the airstream, you probably
won't see a bunch on the belly. ANOTHER PLACE is a clogged
air/oil seperator on the vacuum pump if a wet pump is installed.
They can pump much oil overboard and still function.

Jon Kraus wrote:

You are correct... For that matter worn valve seals too...

'scuse me??? Which version of the "old 300" are we talking about, here?

Happy Flying!
Scott Skylane
N92054

On Sun, 24 Jul 2005 21:59:10 GMT, ORVAL FAIRAIRN
wrote:

Did he fill it up to the "full" capacity? If so, he could be blowing it
out until the oil level reaches a "normal" operating level, usually
about 3 qt. short of "full."

Exactly. I fly a PA28-180 with a Lyc O-360 engine. Oil capacity is 8
quarts, but the engine will dump anything over 7 qts in the first
flight or two.

In the OP's case, losing 3 qts this way seems like a lot to me...
What is oil capacity on an the 172's engine (O-320, or is it a cont
O-300?).

-Nathan

On Sun, 24 Jul 2005 14:20:28 -0500, Greg Copeland wrote:

I'm posting on behalf of my father. My father has been flying a friend's
older 172. The 172 was recently flown on a 8-hour round trip. During this
trip, the plan burned 3-quarts of oil. On return, a compression check was
performed. All came back with 75's or better. A check for
leaks did discover two *very minor* leaks but nothing which would account
for 3-quarts in 8-hours.

The engine bay was not covered with oil and no pools of oil were found.
There is not a large streak of oil on the bottom on the plane as one would
expect if it were simply leaking.

All this makes us think that the plane really is burning the oil but
wouldn't the compression check yeild much lower results if it were burning
that amount oil? Where's the likely suspect here?

Thanks in advance,

Greg


Guys, thanks so much for your time and answers. I'll happily forward your
replies and see what they come up with.

Sincerely,

Greg