M20C Oil Leak Questions

[Tater]

Hi All,

I'm pretty close to owning my first Mooney and while I'm pretty darned excited about it I'm trying to make sure that I don't end up with a plane I should have passed on. Pre-buy is complete and the owner is correcting some things that the pre-buy turned up. The one item on the list that I don't know about though is an oil leak. The pre-buy A&P said it might be nothing to worry about, might also be something bad but that the engine is too dirty to see where the leak is coming from. The owner assures me that it is only a nuisance leak, but it isn't like he is 100% impartial.

The plane: 1963 M20C, 1200 SMOH, 20 STOP IRAN, compressions 76, 74, 74, 74/80 per pre-buy A&P. Current owner has flown it for 17 years, averaged about 70 hours a year. Selling because he is moving up to a Columbia.

Me: 120 hours in a C150, engineer for factory equipment. So a decent amount of machinery knowledge but very little directly with planes and none with Mooneys. Can definitely use input from folks here that know a lot more than I do.

Plans for plane: fly around the Pacific NW for fun, use for instrument ticket training. If things go well eventually (5 years??) move up to something with FIKI.

The owner just sent me this image to show what the leaks look like (I'm on the West coast, plane is on the East coast). He is saying that the oil is just oil that has leaked from the filter during changes and ended up pooling in the lower cowling. This sounds believable to me, but I don't have enough experience to know. What do y'all think? Something to worry about? Look completely normal? 

[carusoam]

See if this is better...

 

Keep in mind...  not all leaks are the same... some can be fixed with a screw driver... other require an overhaul to fix...

The purpose of a pre purchase inspection is to identify what is leaking, and how much it will cost to fix...

A case crack would be bad... an oil return line is an easy fix...

What leak do you have?

PP thoughts only, not a mechanic...

Best regards,

-a-

[Tater]

It that what right side up looks like? I meant it when I said I can use advice!

 

[carusoam]

Let’s find the nuisance leak prior to you taking ownership of it...

Mooneys don’t have any normal oil leaks...

Best regards,

-a-

[Prior owner]

Any more pics of the engine compartment? There is plumbing there for an oil/air separator, but I don’t see the canister....

Edited April 13, 2021 by PilotCoyote

[Tater]

I don't have additional pictures right now but if there are any angles to look at I can ask for more pictures.

The engine is getting all new hoses right now so I'm guessing that's the reason for the missing oil/air separator, guessing.

[Skates97]

Have the engine washed down, have them put some fluorescent dye in the oil, fly it around the pattern once, then put a black light on it. 

Any more flying than once around the pattern may likely blow it all over and you won't have any idea where it is coming from. It is not uncommon to see the oil showing up in a different area under the cowling than where it is originating from. 

[hammdo]

I’d ask the pre buy AP to wash it down (pay him of course) and do the dye. I’d want to be 100% sure it’s not a cracked case and I’d want to know where the oil is coming from. 
 

-Don

[SSimpson77]

Oil leaks are tricky. Hopefully it’s an easy one and the suggestions above should spot it pretty quick. If it doesn’t, then I imagine the seller doesn’t want to spend much time and money diagnosing the multitude of things it could be. Here’s my order of inspection:

oil filter and hoses- tight and not chaffing

oil cooler-should be dry as a whistle.

crankcase seal and oil governor line.

prop governor

oil dip stick o-ring area-sometimes these are tightened down way to tight and eventually leak.

Check the oil drain lines from valve covers to block. All mine were loose on pre-purchase. Even had the previous owner have crank seal replaced 2 times thinking it was that and I replaced it once. Crazy thing about older guppy mouth mooneys, the plenum pressures could cause oil to go forward in engine compartment and out front not down and out. 
 

Please keep us posted to help the next person! 

[JimB]

7 hours ago, carusoam said:

Is that square plastic pan catching the oil? If so, that might be a little more oil than you would like to see.... a few drops on the floor...ok. A contained with a pint of oil, maybe not...

[Boilermonkey]

It's cleaner than my former M20C.   The gaskets leaked a bit even after replacing multiple times...new owner is still trying to figure it out, however, it's not a big deal, just a bit messy.  (Tired silicon/rubber and cork.  With the original and new torque levels.  ..now looking at the surface smoothness).

Not terribly uncommon to have a small drip or two from an oil quick drain.

[Skates97]

59 minutes ago, Boilermonkey said:

It's cleaner than my former M20C.   The gaskets leaked a bit even after replacing multiple times...new owner is still trying to figure it out, however, it's not a big deal, just a bit messy.  (Tired silicon/rubber and cork.  With the original and new torque levels.  ..now looking at the surface smoothness).

Not terribly uncommon to have a small drip or two from an oil quick drain.

When mine was leaking enough that it needed to be replaced I replaced it with a SAF F-50. It is a two piece drain. There is a cap that screws on and acts as a second seal of sorts if the one in the valve leaks. The only downside is that to drain it you need to make sure you have the F50-180 opener that screws on the valve. It comes with it when you buy it and I just keep it in the little box in the plane where I have a couple spare wrenches, spare spark plug, and a couple quarts of oil.

https://www.aircraftspruce.com/catalog/eppages/saf_airF62.php?clickkey=5469

[Ragsf15e]

They all leak a little, and usually it’s no biggie.  Sometimes is pretty hard to know for sure where it’s coming from because it blows all over the place in there, drains down, and a little looks like a lot.  The posts above narrow down the normal places to look.

That being said, I’d try to have the mechanic clean and narrow it down.  Especially with the recent cylinder work.  You’d like to make sure you don’t have an issue with that workmanship.

Is this mechanic different than the person that did the cylinders?  Hopefully?

Edited April 13, 2021 by Ragsf15e

[rbridges]

18 minutes ago, Ragsf15e said:

 

That being said, I’d try to have the mechanic clean and narrow it down.  Especially with the recent cylinder work.  You’d like to make sure you don’t have an issue with that workmanship.

 

Precisely, I've had my plane 10 years and get oil here and there, but I know it's history.  

[PT20J]

There is no way to tell whether it's a big deal or a little deal until you determine the source of the leak. Some are trivial (oil drain back tubes), some are very expensive (cracked crankcase), and some are a constant nuisance, but no danger and expensive to fix (leak at crankcase parting seam).

[Tater]

Thanks so much for all the great input!

All the hoses are coming off right now to get replaced, which I think is the reason for the big catch pan in the picture, owner says there are just couple of drops on the hangar floor normally.

I'm going to go ahead with the recommendations above to have the engine cleaned and fluorescent dye added to track down the leak source. I'll make a post when I get some results so everyone gets to find out the answer.

[Robert Hicks]

Mine had a small leak at the base of the #2 cylinder. Log books showed it had been chased for a decade. Mechanics kept changing the cylinder o-ring. Turns out it was a cracked case.

[Jim Peace]

When I got mine there was a small leak on the underside of the engine coming from a gasket.  Tightened a half turn with a screwdriver and has not leaked in 600 hours...I hope you have the same luck....