Mysterious slow Oil Leak

[Chimpanzee]

To the more knowledgeable:

I have slow oil leak in my 20 C that drives me nuts. I have oil in the front gear housing, on bot sides of the gear well and trailing along the bottom of the fuselage. My oil pressure is stable, the oil usage seems normal too. Here is what I have done: First, I though it was a problem from the retrofit angled oil spin adapter (ECI), so the gaskets at the accessory housing were changed. This did not seem to make any appreciable difference, so I sprayed the engine down, ran it according to piloto's instruction (thanks man !) and checked. Small leakages from three of the oil return hose connectors, and a runner on the back of the oil pan. Had all four rubber return hose connectors changed, as well as a new pan gasket installed. Run-up be mechanic confirmed no leak. Flew it four two hours and again had oil in the front gear housing (less than before however). Now I am lost for an explanation. The engine seems dry. Is there any possibility that the oil comes from the breather line and is somehow ducted into the gear housing, giving the impression of an engine oil leak ?
Puzzled
Norbert

[takair]

My 1964 E is similar.  It has done it through both engines. It comes from the breather.  I'm pretty sure it gets in the gear well because of the lower pressure. That said, it is not a lot. It is what I would call a "trace" of oil, almost a mist.  Is yours more than that...a true trickle?

[carusoam]

Thoughts that come to mind...

(1) The oil return lines can supply a huge mess. They also have a drip hanging from them often. Recheck the hose clamps for proper tightness.  So many clamps...

(2) I think José has detailed how to catch the oil departing from the breather.  The equivalent of a small plastic bag(?) this usually leaves a tell tale sign down the belly.

High cylinder pressure combined with loose fitting rings can allow exhaust to pressurize the engine case.

(3) Prop seal is another pain.  It's tell tale sign is usually distributed on the windshield.

(4) Case crack near the cylinder studs. Somebody posted a picture of one of these the other day.

(5) Any hose fitting from the oiler cooler or prop governor is worth a check.  These all are external and easy to look at.  See how old the governor's seal is.

(6) The back of the engine has a bunch of things that can leak, the magnetos are in that area.  A loose mag may give a sign while it leaks.

(7) The valve covers have old cork seals if they haven't been updated recently. Check the screws for tightness.

My old O360 taught me a lot.  It's dark black oil was easy to find.

These are thoughts of a Mooney pilot.  Not to be confused with those of a mechanic...

Best regards,

-a-

Edited October 4, 2015 by carusoam

[Hank]

Question, Chimp:  how much oil do you try to keep? I fill up to just over 6 qts (I put in 7 when I change it), and will add when the level approaches 5 on the dipstick. Pour in 7, fly once around the pattern, it will fall almost 1quart on the stick due to oil getting into the (dry) filter. For a long trip, I'll add a half quart if I'm below 6, or a whole quart if I'm down to 5-1/2 or so. I also keep a full quart in the baggage area. 

Anything much over six quarts just goes rapidly onto the belly. I generally get ~12 hours after oil change before I have to add anything; the last quart seems to last 6-8 hours. I change it every 50 tach hours.

[DXB]

My 1964 E is similar.  It has done it through both engines. It comes from the breather.  I'm pretty sure it gets in the gear well because of the lower pressure. That said, it is not a lot. It is what I would call a "trace" of oil, almost a mist.  Is yours more than that...a true trickle?

I'm confused. Doesn't the breather connect to a hose that dumps out through the left cowl flap? If so how does it jump over to the nose gear well?  Go easy on me-  I admit that my understanding is rudimentary.  

[MB65E]

Yes... Front gear housing threw me off a bit too. If it's up front by the starter ring gear, I would stick my finger behind the flywheel inside  and see if/how oily it is. If it's wet, you might need a crank seal gasket. 

Oil patterns amazed me when I had any issue with crank seals. 4 seals later...

 With the stock baffling/doghouse I would get build up on the left inside portion of the dog house. Then it would blow around the engine and make a mess. Oil would also be blown up over the top cowl then all over the airplane.  Also, The dipstick can come loose easily. I think due to the exhaust restrictions on the right side, the air/oil patters flow better to the left side, thus covering the left nose gear door. Mags, and prop governors can leak too.

I have had really good luck with the permetex ultra black sealant with sealing case halfs, warped standoff plates, crank seals (external), thru bolts, and many other areas. I have had better luck recently with this process vs any aviation product available. (Plyobond, pro-seal, Locktite, halyomar, etc). If your nearing an oil change, some UV dye may help. Clean everything really well, night engine run, with black light. Careful of the prop!!

Be sure to flush the oil with fresh oil once you are done with the Dye. I wouldn't recommend flying with it. 

I don't want to be the bad guy, but check the case for wetness behind the starter near the #2 lower cylinder attachments. It's really hard to see if it's cracked. Mine had a 5in crack in it. Oil would streak out the left cowl cheek almost to the side window. It was missed by a MSC annual...

It's the most rewarding feeling once you find the leak!! I would know just after takeoff once I closed the cowl flaps if I had fixed it or not. So nice to wipe bugs instead of oil from the windscreen. 

This pic was after a 15 min flight. I finally changed the crank seal one more time. Then sealed the front case halfs and crank seal together. No more oil leaks!!

Great Luck,

-Matt

 

 

[Guest]

Have you checked the vent line from the fuel pump?  It exits the cowl through a small metal line in front of the nose gear.

Clarence

[takair]

DXB--good question.  It does come out of the left cowl flap, but mine is closer to center.  I'll have to think about it some more.  Doing my annual now, so I'll take a closer look.  

 

After reading MB65E's post, I wonder if I read the original post wrong.  Is the oil at the front of the LANDING GEAR housing or within the RING GEAR housing?

[Chimpanzee]

The oil is in the nose gear housing, on the inside of the gear doors an on the gear linkage. Overfill might be a factor, (I run between 5.5. and 6.5), will attempt to go with Hank to run between 5 and 6. However, overfill should show on the belly and not inside the gear housing I think. I will check the breather line for cracks / holes and the fuel pump vent line as suggested.

Norbert

[carl]

The oil is in the nose gear housing, on the inside of the gear doors an on the gear linkage. Overfill might be a factor, (I run between 5.5. and 6.5), will attempt to go with Hank to run between 5 and 6. However, overfill should show on the belly and not inside the gear housing I think. I will check the breather line for cracks / holes and the fuel pump vent line as suggested.

Norbert

My 67 E is the same . A real oil dripper  .I think I could use some new seals and tightening of some bolts. my mechanic says he can fix any leak if he can pull the engine and crack the case. And then it might be from me spilling oil during oil change.  

[takair]

I'm confused. Doesn't the breather connect to a hose that dumps out through the left cowl flap? If so how does it jump over to the nose gear well?  Go easy on me-  I admit that my understanding is rudimentary.  

Well, after looking at it some more, I have to agree with you.  I think in my case it is sloppy filter changes, a little from the intake manifold drain and perhaps a minor leak in the prop governor (but that could also be my sloppy oil changes).

[Shadrach]

Almost anytime oil is spilled in the engine compartment, it ends up revealing itself as a spill on the nose gear/front tire. It will take several flights and or a good cleaning before it stops marking the gear/front tire. It takes very little oil to make a huge mess!

Edited October 10, 2015 by Shadrach

[Chimpanzee]

Finally found the leak(s) - Closure Notice

Thanks for all the input guys! I had probably told you that the leak had plagued me for some time. And to make matters worse, I am in the States on leave about twice a year for  3-4 weeks, so I am always pressed for time.
Anyway, with the leakage I had what I think was a combination of leaks. The oil return hose rubber elements were leaking, but not much. That was taken care when the engine mounts were changed. (see above). But there was still a substantial oil leak. More engine washing and inspection by me and my trusted mechanic told him that the oil pressure line fitting to the prop governor was the culprit. That was easily fixed with Teflon. Admittedly I was sceptical, but after return from two hours flight, there oil leak was gone. I was very happy indeed. 
Now all I have is a little oil mist inside the gear housing, but it barely moists a paper towel when wiping. The horrible streaks on the belly have gone, and with them the anticipation that the engine might have something horribly wrong with it. Flying is much more relaxed now! I really have to thank my mechanic (an old hand), and we had a few beers to celebrate.

Chimpanzee

 

[Guest]

Teflon is a No No in aviation.  Pipe thread fittings should be sealed with Seal lube or Loctie 569 hydraulic sealant.

Clarence

[Shadrach]

Teflon is a No No in aviation.  Pipe thread fittings should be sealed with Seal lube or Loctie 569 hydraulic sealant.

Clarence

Why do so many A&Ps use it? I have seen it many aircraft. I use titeseal but it's quite a bit pricier than Teflon. Why is Teflon a No No?

[Guest]

Teflon tape shreds and falls off fitting threads and can contaminate the system.  Soluable sealants are better.

ref. AC43.13 8-38 para "f"

Clarence

Edited October 18, 2015 by M20Doc

[Mooneymite]

 Pipe thread fittings should be sealed with Seal lube or Loctie 569 hydraulic sealant.

Loctite is very proud of it's 569.  For a guy who only needs a dab once every 10 years, it's not something I keep on hand.

What other sealants do you recommend?

[StinkBug]

My left gear door always has a trickle of oil on it. None in the wheel well, none on the right side. It's weird what air currents and pressure does.

[KSMooniac]

Tite Seal is good stuff...$20 can should last a lifetime for most of us.

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[Mooneymite]

Tite Seal is good stuff...$20 can should last a lifetime for most of us.

I see it comes in light and medium weight.....any recommendations for a guy who uses a dab every 10 years?

[KSMooniac]

I got light weight and believe that is most common. Someone else likely knows better than I do, though. Either probably does the job just fine.

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[Shadrach]

I believe the "light weight" titeseal is what many engine builders use on the parting flange (with silk thread) to seal the case halves together.