Low Oil Pressure & Temp

[AF M20J]

Hi all, I have a 1981 J with an original A3B6D engine overhauled 700 hours ago.

After the latest annual, I'm seeing substantial oil loss in flight. I'm having to add at least 1qt every flight.

On my last flight, it dropped to 3.5qts remaining after starting with 5+. The flight was only 40 minutes on a cool day at low altitude and 65% power.

On this flight about 25 minutes in I saw the oil pressure decrease to about 55-60.

Everything looked fine on run-up (pressure, temp) so I was pretty uneasy about that in-flight. After landing, I checked the belly and it has clean oil all down it. It wasn't a ton of oil, but it also wasn't dirty, and I only really caught it when I was cleaning it with cleaner and a rag.

Also, there was a fair amount of oil deposited onto the hangar floor the next day after flying. About a 6" diameter wet spot. This isn't usual for my plane.

I looked in the engine compartment to see anything abnormal, but didn't see anything outrageous.

I don't have an engine monitor, only a single digital temp gauge for CHT and EGT. The oil pressure is the classic analog gauge.

OK, now for the wrinkle: I'm overseas in a remote spot and can't easily pop over to a Mooney mechanic. I'll have to troubleshoot before the next flight, which I'll use to get closer to an A&P.

Any ideas of what the cause might be? I'll gladly post pictures as requested.

Thanks for your help.

[ArtVandelay]

Check for oil leaks, try to narrow it down...top/bottom, left/right. Would help to know what your AP did. Obviously check oil filter and oil screen, oil return lines, etc

If oil is clean it will be hard to see, engine might look normal, but using your finger to wipe areas you be able to detect the oil.

Unfortunately the air blows the oil around making hard to pinpoint the origin of the leak.

 

Tom

 

 

[N201MKTurbo]

Loose oil filter….

[anthonydesmet]

ALso check oil drain plug.  Saw this happen to a guy at my field a couple years ago.....owner assisted annual: owner did the oil change.  Asked mechanic to safety tie the plug after the owner hand tightened plug.  Owner thought mechanic would torque tighten plug......mechanic thought owner did because plug was “on”. Long story short and one flight later owner came into hanger and saw about a small pool of oil on floor under engine and on nose tire.  Pulled cowl and plug was loose.  Thank goodness the mech did safety wire.

[carusoam]

Pics help...

Unfortunately, with the lack of detail given... you are going to get some list of 20 things to look for...

 

clean the engine throughly... ground run it... look for oil...

There are

• a dozen seals it can be...
• a bunch of rubber oil lines that can come loose...
• a case vent that is known to throw quarts of oil overboard...
• a drain valve that has been known to stick open in flight and drain the case...
• Then there are the case cracks... near the cylinders
• and the silk thread between case halves..
• There are also some good techniques for hunting for the leaks...
• powder sprays
• UV / glowing additives

Decowl, clean up, take some pics... report back...

PP thoughts only, not a mechanic...

Best regards,

-a-

[AF M20J]

Thank you for the recommended actions.

When I'm able, I'll go through them and report back with findings.

Thanks

[Nippernaper]

Just had a similar problem; turned out to be a loose prop governor. High pressure leaks can expel a lot of oil in a hurry.


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[flyboy0681]

If you can't see oil from a leak, you may be trailing some smoke. That happened to me, ran out of oil yet there wasn't a drop to be found anywhere.

[AF M20J]

OK thank all of you for your time and input, amazingly awesome and responsive community.
I need to tune in more often...

Update:

• I topped off the oil (which was at 3.5qt - so I brought it to 5.5)
• then pulled the cowlings, cleaned everything off, which was all pretty oily in there (liquid oil too, not cakey old stuff)
• took her out and had two people watching while I cranked her over (first without starting): no oil
• then fired it up, warmed it up and ran it up: no oil
• So, I flew it for an hour, and the oil pressure remained a constant 80ish (nice and high in the green) the whole way.

Didn't have time to take off the cowling (yet) but will fly again tomorrow and report back with any apparent leaks/spray marks.

So, at the moment, it seems like it was a "random" occurrence (is there really such a thing in mechanics?)

I'll report back if/when I have more...

[carusoam]

AF,

We don’t have many MSers from Austria...

Feel free to post some pics from your area of the Mooney world! 

also...

Keep your eyes open for the return of the oil leak... things like leaks don’t usually fix themselves...

 

Add to the list of things to check on...

the oil dipstick is in a molded plastic tube.  The tube has been known to unscrew and leak from the bottom... there is a seal there as well...  some have gotten loose over time... you will probably notice the looseness(?) when you check the oil...

PP thoughts only, not a mechanic...

Best regards,

-a-

[FloridaMan]

Get an engine monitor. I resisted for years myself. If you must, think of it as an amortized investment. I had a high oil temp reading on my m20f’s temp gauge. After precautionary landings and nearly leaving it behind, I noticed the needle didn’t drop to zero when I powered off. I pushed firmly with my thumb and discovered it was a poor connection. 
 

Oil temp and pressure generally are inversely related. If you see one dropping and the other remaining constant, but still in the green, start with verifying your instruments. 

[flyboy0681]

16 minutes ago, FloridaMan said:

Get an engine monitor. I resisted for years myself. If you must, think of it as an amortized investment. I had a high oil temp reading on my m20f’s temp gauge. After precautionary landings and nearly leaving it behind, I noticed the needle didn’t drop to zero when I powered off. I pushed firmly with my thumb and discovered it was a poor connection. 
 

Oil temp and pressure generally are inversely related. If you see one dropping and the other remaining constant, but still in the green, start with verifying your instruments. 

When I lost (most of) my oil in flight the first thing I noticed was the factory oil pressure gauge swinging from side to side (I've been told that it was sucking air). I kept checking the oil temperature and it went down about 5 degrees (since it's a mechanical gauge I could only estimate).  We've all been taught during our primary training that if you lose oil, the temp will rise, which is what I was looking for. What I learned after the fact is that it depends where on the engine the sensor is placed.

Since this episode we had the oil pressure feature added to our JPI 700.

[carusoam]

Nice detail, flyboy!

We don’t get to prove/disprove that part of the primary training very often...

Best regards,

-a-

[AF M20J]

Thanks @carusoam, I'll post some pics, where should I paste them?

Well, the oil burp happened again.
Chatted with a mechanic (back in a good location) and he said it might be aligned piston rings, which can happen sometimes.

Double ditto on the Engine Monitor. It is at the top of the list for the next upgrade.

Thread drift, but a lot of mechanics in  Europe don't agree with running LOP.
I only have one temp probe (digital EGT/OAT/CHT) but am experimenting.

[carusoam]

AF,

Find the thread named ‘Today’s flight 2019’

Mooney Pics from Austria will be awesome!

 

Aligned pistons can happen...

But you will find this is not very common...  when it happens, something isn’t right about the cylinder or the rings...

The engine monitor would help you identify the culprit...

Rings being aligned is usually a source for faulty compression readings...

A misbehaving oil ring may be the source of the oil escaping...

 

Operating LOP without an engine monitor also has its challenges.  If the fuel distribution has gone un-even... it can leave a cylinder in a different situation as the one you are using to lean with....

 

Often, if oil is leaving through one cylinder... oil is left dripping out of the exhaust pipe... it doesn’t all get burned up...

pulling the lower spark plugs will reveal what cylinder is misbehaving...

inspecting the oil ring, you may find that it is not working properly... this takes a mechanic to perform...

 

A 1qt per hour oil loss is not anywhere near normal...  it may not stay constant.  It could get much worse. Keep looking for what is not working...

 

PP thoughts only, not a mechanic....

Best regards,

-a-