Very fine mist of oil on cowling, windscreen and horizontal stabilizer source question

[lanejacobs84]

Just did a prebuy and annual on my Dads ‘79 J with a IO-360-A3B6, converted in ‘95. TSMOH 1460. He owned it for 35 years and I grew up in it. In my short ownership it’s burned about 0.75qts in almost 4 hours of flying and is down to 6.25. I owned a ‘66 C previously. 
 

The first flight out of annual I discovered a very small amount of fine mist I think is oil on the windscreen, lower cowling and horizontal stabilizer. No oil on the prop. This is new as I flew it before the annual and no problem. I know there are lots of threads on this which I have read :-)

The mechanic said the prop seal and crank seal looked good. However, my question is, is it possible for the O-Ring (often forgotten I hear?) behind the prop seal to be bad, or forgotten, and for it to leak out of the space between the spinner and prop? I feel convinced that’s where it’s coming from. If the O-ring was forgotten I feel like there would be much more oil since it’s only a very small amount. Just trying to pinpoint the source…

There is also a small amount of oil leaking from the top of the engine case from one of the bolts which is shown in the picture attached. I’ve read about the engine compartment airflow theories… I flew the plane for about 15 minutes after cleaning the engine and you can see how much oil leaked out. Could this also be the likely cause? 

I just don’t want to spend $$$ and time hunting down very small leaks if I shouldn’t be worrying about them…. Or maybe I should be worrying? 

Thanks in advance! Very appreciative of what a great resource Moonespace is. 
 

Lane Jacobs

 

[KSMooniac]

The top case bolts can absolutely be the cause of the mist all over the plane!  Many years ago I neglected to fully torque the very last top bolt when installing the mag harness, and it created a leak that migrated forward, out of the cowl inlets, and back over the windscreen.  Easy fix.  I'd clean everything again, torque all of the bolts, and go fly some more.

[M20F]

It’s the first flight out of annual.  Somebody could have spilled oil filling it up.  I would degrease it down the best you can, fly for an hour with established amount of oil, and see what happens (let it have 24hrs sitting to check the after).  My experience is the old ones all leak.  As long as the consumption is reasonable and consistent I wouldn’t worry about it.  

[Ragsf15e]

I don’t disagree with anyone above but I haven’t had an oil leak get the windscreen yet.  I did have a prop get that fine mist on the windshield though… did the prop get “serviced” at the annual?

[dzeleski]

Random shot in the dark but check the gasket for the oil filter adapter. Mine went bad and promptly shot oil all over the wing, wind screen, and tail.

[lanejacobs84]

2 hours ago, Ragsf15e said:

I don’t disagree with anyone above but I haven’t had an oil leak get the windscreen yet.  I did have a prop get that fine mist on the windshield though… did the prop get “serviced” at the annual?

The prop did not get serviced but they had to pull it off to change the alternator belt. Thats why I'm concerned about the O-ring behind the prop seal...the landing light was not hooked back up (which I caught) when they took the lower cowling off so I am concerned other things were missed too... 

[Fly Boomer]

10 hours ago, lanejacobs84 said:

The prop did not get serviced but they had to pull it off to change the alternator belt. Thats why I'm concerned about the O-ring behind the prop seal...the landing light was not hooked back up (which I caught) when they took the lower cowling off so I am concerned other things were missed too... 

We all wish that mechanics and doctors were perfect as they ply their trade.  They are not, and it falls on us to help mitigate the risk.  Sorry you're having trouble.