Dealing with oil leak, possibly from crankcase seam?

[DXB]

The aircraft: 1968 M20C

The engine: O-360-A1D with original serial # for plane, now ~1400 SMOH in 2000, bought by me in 2013 with 600 hours SMOH on it.

The situation: When I got the plane in 2013, there was very minimal evidence of oil leakage anywhere.  There was a little bit along the front lower case seam above the muffler, which I'm told is pretty normal.  Over my last 800hrs of flying, this leakage has progressed to the point where I see a lot more oil on top of the muffler, front of oil pan and carb, and top of carb heat box. The rest of engine and accessories look clean.  The leak has gotten to the point that I see a few drops on my nosegear tire the day after I park the plane (pic below), never enough to reach the ground. My oil consumption has risen a bit too, though it's not too bad (~7 hrs/qt), and I'm wondering if this bit of leakage with the crankcase under pressure in flight is contributing to the rise. Regardless, it's gotten to the point that I don't want to ignore it any longer. I can live with this level of leak but want to exclude a serious issue and am also worried it will continue to get worse.

The questions:     (1) How do I make sure it's really just seepage through the crankcase seam? (2) If so, I imagine increased blowby on a cylinder could be contributing or might even be the root cause of the problem? (3) Assuming it's deterioration of the seal between the crankcase halves, how would one address it without resorting to pulling the engine and splitting the case (if it came to that, I'd do an overhaul given that it's now been >20 years SMOH)?  I've read about various clever fixes on the interwebs but wanted to get a clear concept of how to diagnose and treat the problem before I start writing checks to a couple A&Ps around here about it. I'd really like to get some more years out of the bottom of this engine, which has done well in my hands flying regularly, despite having sat a lot with previous owners after the last overhaul.

[MB65E]

Permetex ultra black I have found works better than most fuel tank sealants. You could clean everything really well then apply a bead to the case halves. 
Check the inside of the flywheel to make sure it’s not the crank seal. 
Also, go around and torque all of the 1/4in hardware along the case halves. Don’t over torque them, just give them all a squeeze. 
Check all of the oil drain back lines for tightness. 
Most likely it’s probably a case stud that is leaking. I removed several of my case studs and applied anaerobic Loctite with new studs. When a case is overhauled, I don’t think the studs are ever changed. Over time they stretch and no longer seal properly. There is no sealing mechanism for the smaller studs. 
Oil pan gaskets are often suspect as well. One could apply the same principles to the oil pan. 
Overall, your 20 year seals are deteriorating.

-Matt 
 

[ArtVandelay]

I had same issue, was a crack in case close to the alternator...apparently a common problem.

[Skates97]

Clean everything really well and then add fluorescent dye to the oil. Fly it around the pattern once, only once, and only around the pattern. An extended flight will cause it to just blow all around inside the cowling. Shut down and put a black light on it and you will likely see where the leak is coming from. I had a leak that I was chasing for quite awhile and couldn't quite figure out where it was coming from. My AP/IA and I did this and with the black light it was plain as day that it was coming from the oil quick drain. To give an idea of how much everything blows around in there, the leak was from the quick drain but in addition to oil getting spread all over it was actually coming up out of the cowling in front of the #2 cylinder and coming back along the top of the cowling. It wasn't enough to even drip on the tire, just make everything a mess with a light coating of oil...

It sounds like your leak is likely from someplace else, but this method might help you zero in on it.

He cleaned the engine really well before I took it around the pattern. This is after that short flight, it was easy to see where the oil/dye was coming from.

Here you can see oil coming out the front of the cowling from that leak (at the back/bottom of the engine). It really blows around in there.

[carusoam]

Wheel down...

Common leaks...

• Oil return lines... lots of mini hose clamps of various ages and sizes...  easy to swap in new hoses and clamps...
• Case half seal... a long silk thread that requires splitting the case to replace... Sealant from the outside is sometimes viable...
• Quick drains... 50 year seals often leak... new quick drains are a much better design....
• Engine cracks... up by the cylinders... sometimes bad news...
• other seals known to leak... oil pan, accessory case, and governor... not hard to replace...
• Rocker cover seals... original were cork, silicone seams to be all the rage now... proper even torque with proper hardware works really well...

Common techniques...

• Clean the engine really well....
• Dry the engine...
• Use of foot powder spray... a dry powder that adheres to the engine surfaces... any leak will show in the powder surface...
• Use of oil dye... minimal amount of flying or engine running... once it leaks out... it spreads far and wide from the initial leak...
• There are special products for engine leak detection.... probably foot powder with a more appropriate label....

My C got all of the oil return lines replaced... solved lots of oil leaks...Rocker cover seals too...

Anything that can get old, will get old under the cowl....

PP thoughts only, not a mechanic...

Best regards,

-a-

[FloridaMan]

Where are you located? There’s a shop in Florida that fixed mine on my m20f’s previous engine after numerous other shops failed. 

[carusoam]

Dev’s up in North Philly...
probably too corona Busy to get to Florida...  But, you never know... 

Best regards,

-a-

[kmyfm20s]

My J had oil leaking from one of the through bolts.  I ended up replacing it with a .001” oversized one that took care of the problem.

[DXB]

Thanks all for the multiple relevant and helpful suggestions.   I think we found the source. 

So with help of a fellow mooneyspacer, I cleaned it up and added a splash of dye to the oil.  The leak was not apparent after a ground runup.  After a trip around the pattern, there were a couple of fresh oil streaks on the lower firewall just to the left of midline.  The crank case including the bottom seam stayed perfectly clean, and there was a faint strip of fluorescence visible across the oil pan seam under UV light, but nothing dramatic.  Then my helper saw a splash of oil under the left mag (a Surefly) that I had completely missed.  That area is particularly difficult to visualize or access on a C model, in part because of the position of the battery box.  A borescope view seemed to show the lower nut holding on the Surefly to be loose.  We removed the battery box (a total PITA - held by 4 bolts, with the nuts on the other side of the firewall), and that gave  a semi-unobstructed view :

 

Big thanks to @cferr59 for having the sharp eye to catch this catastrophe in the making. Access and visibility are so tight in that area that I'm not sure I would have ever seen it. I believe there are a number of folks who've wound up in a field, or worse, because of mags coming off in flight.  I'm a little rattled that I'd flown about 6 legs since I first noticed a few oil drops on the front tire the day after a flight. When I didn't see a clear source under the cowl, I thought it was just progression of the small, nonserious leaks all older engines have. @Skates97's point that the oil blowing around can make even serious leaks hard to localize is nicely illustrated here.  It's also unfortunate that the difficult access problem that made the source of the leak hard to see is probably also what led to the error someone made in torquing that nut. The last irony is that I switched to a Surefly primarily for reliability after my old left mag failed in flight precisely 500 hours after IRAN.  I am now permanently terrified of anything that has to do with mags.

As far as fixing it, I think it's enough to have an A&P replace the lock washers, retime the Surefly, and torque the nuts to spec?  Now to find someone willing to do the job in my hangar...plane ain't going nowhere right now.

 

[orionflt]

5 hours ago, DXB said:

As far as fixing it, I think it's enough to have an A&P replace the lock washers, retime the Surefly, and torque the nuts to spec?  Now to find someone willing to do the job in my hangar...plane ain't going nowhere right now.

 

I would swing over to help you, but with me bouncing between here and Virginia I have very little time to run to Philly. If it's not fixed by next friday, let me know and i will try to fly over to help you out.

Brian

[shawnd]

Good catch and good luck! That’s scary indeed. I am trying to confirm oil leaks in my plane too. After your post, I am going to focus harder in the area near the mags.

[47U]

8 hours ago, DXB said:

We removed the battery box (a total PITA - held by 4 bolts, with the nuts on the other side of the firewall),

If you have the stock windscreen and if your wiring behind the panel is somewhat orderly (allowing you to get your arm down below the hydraulic reservoir), you can reach all of the battery box hardware inside the cabin through the avionics access panel.  It’s no fun crawling into the footwells to get to hardware on the firewall.  BTDT.

I love the look and tangible benefits of the 201 windscreen, but I’m not willing to lose this access.  It’s just too valuable to me.

tom

[carusoam]

Great pirep Dev!

Sending a PM your way... @DXB

Best regards,

-a-

[DXB]

9 hours ago, orionflt said:

I would swing over to help you, but with me bouncing between here and Virginia I have very little time to run to Philly. If it's not fixed by next friday, let me know and i will try to fly over to help you out.

Brian

Thanks Brian!  I just got it taken care of today, so all good.  Mag retimed and resecured, leak stopped. 

6 hours ago, 47U said:

If you have the stock windscreen and if your wiring behind the panel is somewhat orderly (allowing you to get your arm down below the hydraulic reservoir), you can reach all of the battery box hardware inside the cabin through the avionics access panel.  It’s no fun crawling into the footwells to get to hardware on the firewall.  BTDT.

I love the look and tangible benefits of the 201 windscreen, but I’m not willing to lose this access.  It’s just too valuable to me.

tom

Yeah I have the 201 windshield - I had it installed myself and really like it, but I was cursing it was today while I was on my back in front of the pilot seat under the panel.