Annoying oil leak

[jnisley]

My mechanic and I have been trying to find and stop an oil leak that only shows up in flight (the oil possibly doesn't get hot enough during a ground run) , it always shows at the same spot and is bad enough that the belly of the plane has oil all the way to the tail, it appears like it's coming from the oil suction screen plug because there's no oil drips/runs above the plug. (See attached photos)

The plug has been tightened then later removed, inspected and a new gasket installed but there was no change when took it on a 40 minute flight this morning. The oil pan bolts have been tightened as well with no change.

Any help would be appreciated.

[Andy95W]

Yup. Oil leaks are a b!t€h.

Unless there is a crack at the suction screen area (doubtful) I don't think that is your culprit. I do think, IMO, that since the suction screen is the low, rear part of the engine, that is where oil would tend to go before dropping off.

Keep looking, if possible from top to bottom. The most likely culprits, based on the volume, I would guess would be either the oil return lines from the cylinder heads or the case/oil pan mating surfaces.

You've got a TN by your type- does that mean turbo normalized? If so, you may want to check your exhaust. I'll freely admit I don't know much about your TN system, but high pressure oil to cool your turbo could certainly be leaking internally. Stranger things have happened.

Please keep us posted.

[orionflt]

I had a tough one to find, turned out the prop governor was leaking from a shaft seal under the spring. The oil would run down the firewall and trail back under the fuselage.

Brian

Sent from my iPad using Tapatalk

[jnisley]

Yes, it is turbo normalized, we did check the turbo components, oil lines etc, we replaced one of the push rod tube seals, the oil return lines are dry, three times in the last two weeks we washed down, dried (engine area) and test flew the plane, not a drop of oil anywhere except around this plug and immediately below it.

Has anyone used dye/light to find leaks?

[jnisley]

We did check prop governor area but I'll check again using a mirror.

[Guest]

I've seen the suction screen nut installed cross threaded before. I had to buy a tap to re thread the hole. If it only leaks after flight, you may be able to pressurize the crank case through the breather with a shop vacuum after landing to confirm your theory.

Clarence

[Andy95W]

Yes, it is turbo normalized, we did check the turbo components, oil lines etc, we replaced one of the push rod tube seals, the oil return lines are dry, three times in the last two weeks we washed down, dried (engine area) and test flew the plane, not a drop of oil anywhere except around this plug and immediately below it.

Has anyone used dye/light to find leaks?

Wow. Very thorough. Don't think I can add anything to that.

Please keep us posted. I'm looking forward to learning something new when you get it tracked down.

[kerry]

Check your fuel pump.  I tightened the screws top and bottom that sandwich the gaskets. I was getting oil that was making a mess on my firewall then going to the belly.  It would only occur after flying the airplane.  After I tighten the screws on the fuel pump it solved my problem.

[jnisley]

Thanks for all the suggestions, we'll keep looking!

[jetdriven]

Mag gaskets often leak after adjusting them.   Also, take a wrench to the prop governor stud nuts. My Boss's Arrow was leaking in that area, each of the nuts took a half turn to get tight! 

[Mooneymite]

Mag gaskets often leak after adjusting them.   Also, take a wrench to the prop governor stud nuts. My Boss's Arrow was leaking in that area, each of the nuts took a half turn to get tight! 

+1 on the mags.  Mag oil leaks can be very confusing because of the direction (mis-direction?) of airflow on the accessory section.  I had mag leaking oil and that was about my last suspicion.  Very sneaky.  It was the last place I looked because after I stopped the leak, there was no reason to look further...

[BigTex]

Could also be the front engine seal. Mine was leaking and had old all over my mags.

[N201MKTurbo]

I wish my leaks were that small.

[jnisley]

Several things things happened today that gives us hope that we can fix this leak, first, I bought a new inspection mirror (the old one was scratched up) and immediately found a drop of oil on the small plug on the bottom of the prop governor which is above and slightly back from the sump screen plug (see photos) second, I wiped everything down then did a runup getting to oil up to 150 degrees, occasionally cycling the prop, I shut down and bingo, there was a drop of oil on the plug, three times I wiped the plug clean and did a runup, three times there was a drop of oil on the plug after shutdown.

It's in a difficult spot (as is most everything on a Mooney) and my mechanic isn't able to look at it till Monday so....I must wait.

[jnisley]

I wish my leaks were that small.

I don't consider it a big leak until it drips off my tail skid and this one does:)

[Guest]

That plug is in the Lycoming governor drive adapter, not the governor itself. Remove it, clean the thread thoroughly and reinstall the plug with thread sealand and torque it per the Lycoming manual.

Clarence

[Mooneymite]

As is obvious, an oil drip can form at any low spot while the offending leak may be higher, or in some cases far away. One of the devils in an air-cooled engine is the constant flow of air carrying leaking oil everywhere.

[jnisley]

From what I could tell using the mirror it is coming from the plug but......it could be coming from elsewhere.....hopefully not:(

[jnisley]

That plug is in the Lycoming governor drive adapter, not the governor itself. Remove it, clean the thread thoroughly and reinstall the plug with thread sealand and torque it per the Lycoming manual.

Clarence

You are correct.

[fantom]

Just wondering....anyone ever have an oil leak that wasn't 'annoying'?

[bonal]

Check the oil filler tube for tightness into the case also.

[jetdriven]

That gasket under the dipstick tube is a terrible idea in that application.  The tube is made of plastic and the threads stretch, the tube loosens, and the gasket leaks. a thin O-ring in its place can be dogged down and it wont leak again.

[scottfromiowa]

Check the oil filler tube for tightness into the case also.

+1

[Piloto]

Three years ago I had a similar annoying oil leak that showed on the hangar floor when I filled above 7 qts. It turned out to be a very small needle hole on the sump casting. The sump is made out of a casting process that is subject to some porosity. I fix the leak with Marine Tex and no leaks since then.

 

Another leak that really puzzle me that only showed up after long stay trips. I could see the leak on the hangar floor but could not trace it back to the plane. After a dozen trips I found out that the leak was coming from my Ford Explorer when I park it in the hangar.

 

José  

[jnisley]

Maybe it's my Ford Expedition;)