Oil on Windscreen, what to do

[gwav8or]

So this weekend after almost three hours of flying to a local flyin and back, I noticed oil on the windscreen, top of cowling and front of cowling.  Actually, I noticed it during descent back into our home airport.  I had my wife with me and didn't mention it to her because I didn't want her to be nervous or frightened.  Of course, this happens the day before I'm to take the Mooney to the avionics shop for an avionics upgrade that I've been waiting for since about April.  Just my luck.

So, I text my mechanic on Sunday to see if he can help me out and check out the plane on Monday morning.  I was thinking it was either a prop hub oil leak or a crakshaft seal leak.  Nope.  The leak is coming from one of two crankcase bolts on the front of the case, right behind the prop.  Not a good thing, but mechanic said he tightened the bolt a bit (made sure it was torqued to spec) and said it should be fine and would be more of a nuisance than dangerous.

Mechanic said that the proper way to fix it is to split the case and repair/replace the "gasket" which is literally just a piece of silk thread.  Of course if the case is split, one might as well inspect/repair/replace the internals and do an overhaul.  An overhaul for a gasket/bolt? Good grief!  I do NOT want to split the case yet!  I've only owned this bird for a little over a year. 

The mechanic said he could do a temporary fix but I wanted to reach out to the braintrust and see what might be a suitable fix to get me a few more hours down the road.  So WWMSD?  What Would Mooney Space Do? :-)

[N201MKTurbo]

Wow, you have the original factory upholstery. It should be in a museum.

I've never seen that much oil come out of the top of the engine at a parting line. I have seen it make a messy seep. I have had luck loosening the bolts, cleaning the parting line with IPA and a toothbrush, letting it dry then putting Loctite on the parting line and re-torquing the bolts.

[gwav8or]

42 minutes ago, N201MKTurbo said:

Wow, you have the original factory upholstery. It should be in a museum.

I've never seen that much oil come out of the top of the engine at a parting line. I have seen it make a messy seep. I have had luck loosening the bolts, cleaning the parting line with IPA and a toothbrush, letting it dry then putting Loctite on the parting line and re-torquing the bolts.

Yep, the interior is original and honestly in pretty decent shape.  My plan is to redo the interior once  I get the avionics done.  BUUUUT this oil leak issue may derail my plans. 

However, I don't believe the mechanic meant that the leak was at the parting line, if by that you mean where the case halves come together?  He said it was coming from the bolt itself.  He showed me but unfortunately I didn't get a pic.  There was a small amount of oil that literally looked like it was coming from the bolt hole.

[PT20J]

Leaking from the parting line and the bolt holes is essentially the same thing because the silk thread (actually two threads in parallel) runs between the bolt holes and the interior of the crankcase. Lycoming has a repair technique that involves cleaning the area, loosening the bolts, drawing a vacuum in the crankcase and applying green loctite. This was described at the factory maintenance class I attended. I don’t believe there is a document describing it, but supposedly your mechanic can get the details by calling Lycoming tech support.

Skip

[N201MKTurbo]

20 minutes ago, PT20J said:

Leaking from the parting line and the bolt holes is essentially the same thing because the silk thread (actually two threads in parallel) runs between the bolt holes and the interior of the crankcase. Lycoming has a repair technique that involves cleaning the area, loosening the bolts, drawing a vacuum in the crankcase and applying green loctite. This was described at the factory maintenance class I attended. I don’t believe there is a document describing it, but supposedly your mechanic can get the details by calling Lycoming tech support.

Skip

I never used the vacuum. That's a good idea. Capillary action seems to work OK.

[Vance Harral]

The amount of oil your engine is spitting out is more than ours, but the pattern is similar.  If it's new and has never happened before, it's worth debugging, and sounds like you've done that.  But among the options of "what should I do about this", one is "nothing at all".

Many aviation engines leak a small amount of oil for long periods of time without incident.  In our case, we know it comes from a combination of the pan gasket, pushrod tube gaskets, and probably a small amount from the case half seal (thread) like you.  We have chosen the "watchful waiting" approach.  It's been working for over a decade.  Engine is currently at 32 years and 2400 hours since overhaul.

I hope I'm not giving the impression that I'm cavalier about this.  The thing that bothers me most about it is not the leaking that's happening now, but the way the current leaks could mask new leaks.  However, it's also true that an attempt to fix the current leaks could actually make things worse.  When we look at the risk analysis in the cold light of day, it feels like the genuinely safest and most practical thing to do is nothing, until the status quo noticeably changes.  Again, "noticeably changes" is a risk, because we're probably more likely to dismiss a developing problem as same-old-same-old.  But it's a risk we're balancing against other risks that are equally weighty.

[EricJ]

41 minutes ago, N201MKTurbo said:

I never used the vacuum. That's a good idea. Capillary action seems to work OK.

Green loctite is all about capillary action.    That stuff locks anything within visual range of the application. 

[EricJ]

1 hour ago, gwav8or said:

Yep, the interior is original and honestly in pretty decent shape.  My plan is to redo the interior once  I get the avionics done.  BUUUUT this oil leak issue may derail my plans. 

However, I don't believe the mechanic meant that the leak was at the parting line, if by that you mean where the case halves come together?  He said it was coming from the bolt itself.  He showed me but unfortunately I didn't get a pic.  There was a small amount of oil that literally looked like it was coming from the bolt hole.

I'd fly it and see what it does.   Maybe just fly it to your avionics appointment.   If it doesn't do it again you're done with it, and if it does it's unlikely to damage or stop the engine (just be annoying) and you'll have some good ideas of what to do next.

And you're right that splitting the case is not worth it, as there's a lot of mandatory stuff to do if the case is split (according to Lycoming) and you're teetering on just doing an overhaul at that point.   Totally not worth it for a leak.

[Skates97]

It wouldn't hurt to double check where it is coming from. I had a similar issue and it was actually the oil quick drain. There is some reverse airflow and the leak could be lower down and oil getting pushed up and out the front by the airflow.

Clean the engine well and add some fluorescent dye to the oil. Fly it around the pattern once, anymore flying than that and oil will be everywhere and hard to pinpoint the leak. After landing put a blacklight on it and the leak should be obvious. This was the leak from my quick drain after a trip around the pattern.

[JimB]

That looks like a front seal to me. Maybe clean it up and see if the prop is slinging it outward. Even a front seal might show some on the front of the case. For it to all of the sudden spring a leak at the front of the case seems a bit odd. 

[Pinecone]

1 hour ago, PT20J said:

Leaking from the parting line and the bolt holes is essentially the same thing because the silk thread (actually two threads in parallel) runs between the bolt holes and the interior of the crankcase. Lycoming has a repair technique that involves cleaning the area, loosening the bolts, drawing a vacuum in the crankcase and applying green loctite. This was described at the factory maintenance class I attended. I don’t believe there is a document describing it, but supposedly your mechanic can get the details by calling Lycoming tech support.

Skip

A friend of mine did this to his Cardinal and it worked great.

[JimB]

2 hours ago, PT20J said:

Leaking from the parting line and the bolt holes is essentially the same thing because the silk thread (actually two threads in parallel) runs between the bolt holes and the interior of the crankcase. Lycoming has a repair technique that involves cleaning the area, loosening the bolts, drawing a vacuum in the crankcase and applying green loctite. This was described at the factory maintenance class I attended. I don’t believe there is a document describing it, but supposedly your mechanic can get the details by calling Lycoming tech support.

Skip

This gets described a lot online. I wonder why Lycoming doesn't publish a SL with the procedure in it? 

[KSMooniac]

14 minutes ago, JimB said:

This gets described a lot online. I wonder why Lycoming doesn't publish a SL with the procedure in it? 

Because they could sell more bearings and other parts if more cases were split? 

 

[gwav8or]

1 hour ago, EricJ said:

I'd fly it and see what it does.   Maybe just fly it to your avionics appointment.   If it doesn't do it again you're done with it, and if it does it's unlikely to damage or stop the engine (just be annoying) and you'll have some good ideas of what to do next.

And you're right that splitting the case is not worth it, as there's a lot of mandatory stuff to do if the case is split (according to Lycoming) and you're teetering on just doing an overhaul at that point.   Totally not worth it for a leak.

Yeah, I flew it about 30 mins to the avionics appointment yesterday.  Still had a little oil spray on the windshield.  I'll prob let it ride for now.

The logical side of me tells me that it's nothing more than a nuisance.  The emotional side of me causes me to think about it while flying and wondering if my pax see it and are worried about it.  The frugal side of me wants to do the Lycoming/Green Loctite treatment and see what happens.

Either way, I've got 4-8 weeks to decide what to do since the plane is with the avionics guys now.

[EricJ]

1 minute ago, gwav8or said:

Yeah, I flew it about 30 mins to the avionics appointment yesterday.  Still had a little oil spray on the windshield.  I'll prob let it ride for now.

The logical side of me tells me that it's nothing more than a nuisance.  The emotional side of me causes me to think about it while flying and wondering if my pax see it and are worried about it.  The frugal side of me wants to do the Lycoming/Green Loctite treatment and see what happens.

Either way, I've got 4-8 weeks to decide what to do since the plane is with the avionics guys now.

Yeah, use the time.    As others mentioned, it could also be the front seal or something else. 

[PT20J]

6 hours ago, JimB said:

This gets described a lot online. I wonder why Lycoming doesn't publish a SL with the procedure in it? 

Maybe because it was actually developed by Continental (or so they told me). 

[Echo]

Sorry this happened. I replaced two prop seals before the case half separation was identified. I was crabbing and looking out side window to land oil was that bad on glare screen. Minimal amount lost, but a Lot of mist.   I overhauled. What is your hours and time since overhaul?

[gwav8or]

Sorry this happened. I replaced two prop seals before the case half separation was identified. I was crabbing and looking out side window to land oil was that bad on glare screen. Minimal amount lost, but a Lot of mist.   I overhauled. What is your hours and time since overhaul?

Total time is around 3800 and TSMOH is about 1200. Last major was quite a long time ago but it’s not making much metal (according to oil analysis) and oil consumption isn’t high. Oil consumption is about a quart every 6-8 hours.


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[EricJ]

3 hours ago, gwav8or said:

Total time is around 3800 and TSMOH is about 1200. Last major was quite a long time ago but it’s not making much metal (according to oil analysis) and oil consumption isn’t high. Oil consumption is about a quart every 6-8 hours.

Sounds like a good engine.   

[gwav8or]

6 minutes ago, EricJ said:

Sounds like a good engine.   

Yeah, I just hope I've not "shaken things loose" with the 80 hours I put on it last year.  Previous owner was only putting 12-15 hours per year on it.  I typically fly it 24/24 and 100 ROP so it's fairly babied.  I'll occasionally fly 25/24 and 75 ROP but that shouldn't be too bad. 

[T. Peterson]

5 minutes ago, EricJ said:

Sounds like a good engine.   

True, but oil leaks are maddening!!! I have been chasing one since I owned the airplane. Airplane is late coming out of annual due to the shop doing their best to find and tame this oil leak. Therefore my wife and I are driving to an event in TN that we had hoped to fly.   I certainly understand the frustration of the OP.

[gwav8or]

3 minutes ago, T. Peterson said:

True, but oil leaks are maddening!!! I have been chasing one since I owned the airplane. Airplane is late coming out of annual due to the shop doing their best to find and tame this oil leak. Therefore my wife and I are driving to an event in TN that we had hoped to fly.   I certainly understand the frustration of the OP.

Yep, it is maddening.  I've tried to learn as much as I can about these engines and even with what I've been able to learn/understand, an oil leak is still concerning.  Especially to my favorite passenger (wife).  She absolutely does NOT like the idea of flying when there's even an extremely minor oil leak.

[EricJ]

11 minutes ago, gwav8or said:

Yeah, I just hope I've not "shaken things loose" with the 80 hours I put on it last year.  Previous owner was only putting 12-15 hours per year on it.  I typically fly it 24/24 and 100 ROP so it's fairly babied.  I'll occasionally fly 25/24 and 75 ROP but that shouldn't be too bad. 

Usually putting time on it is good for an engine.    You may be uncovering some latent issues that need to be caught up on, but often a year or two of that to get all the pending annoyances handled and it gets better.

It sounds like your A&P is familiar with sorting this stuff out, and little oil leaks can be annoying to find, but it also sounds like you're on your way toward getting it handled.   It's the usual joy of owning something with a motor. 

[gwav8or]

6 hours ago, EricJ said:

 It's the usual joy of owning something with a motor. 

LOL no truer words have ever been spoken!

[Echo]

11 hours ago, gwav8or said:

Total time is around 3800 and TSMOH is about 1200. Last major was quite a long time ago but it’s not making much metal (according to oil analysis) and oil consumption isn’t high. Oil consumption is about a quart every 6-8 hours.


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My TSMOH was similar in hours on engine AND I had numerous years of airframe sitting in a hanger of owner in fly in/fly out attached to his house.  Minimal hours/year made the airframe and engine time APPEAR positive, but in reality were major negative.  The sitting is hard on engines and it is common when they have been idle for long periods for the engine to "reward" the new owner with oil leaks.  My case-half separation was making the plane unflyable as the mist made forward vision through windscreen impossible after a two hour flight.  NOT GOOD.  I hope a solution as identified works.  Mine was an expensive lesson.  I repeated with a Missile (high time engine), but had younger co-owners and ejected before engine overhaul.  Back in with a plane that has been flying and appears (always fingers crossed) to be strong and "leak free"...BUT I have less than 35 hours since purchase.  These engines are a crap shoot.  Enjoy the "flying part  "  Scott