Oil spray over windshield and top cowling.

[Mooncharlie]

Hi, last week I took the '62 M20C for a ride. It was a really hot day, around 30°C on ground and flying at 2000' it was around 26/28°C. 

After the second leg, total flight time of 2hs, I landed and noticed some oil over the top cowl, checked through intakes and didn't notice anything strange. 

Sarted the return trip and there was some oil mist coming into the low part of the windshield, at that time the oil pressure was around 60/62 instead of the regular 72, RPM steady and oil temperature according to the day. 

Back in home, engine cooled down and I stared to find the oil leak, nothing on the floor, neither on the front tyre, starter clean, alternator clean, prop clean, also checked for oil with the fingers inside of the alternator pulley to check for crankcase seal and all dry. 

The only place I found oil was in the oil tube screw ending in an "L" shaped connector coming from under the engine (sorry I don't know the proper name), picture attached. 

 Is there any way to check, or maybe directly replace the oring/seal in that connector?

Thanks a lot in advance. 

[Janat83]

Did you check oil level before you fly and after you land, do you know approximately how much oil you lost? 

I don't know if there's any gasket in that oil line elbow fitting, but you might need to check for any cracks in the case, you need to clean the engine and run it on ground then inspect, I'd ground the airplane until you find out the reason for oil leak. 

Not a mechanic but I had to deal with many oil leaks events in my engine. 

[takair]

I would run your finger on the inside of the starter ring gear.  You want to be sure the nose case seal at the crankshaft has not sprung a leak..  I think it could affect oil pressure, but I would think you would have much more oil.  

[MB65E]

There is not a gasket in that 90° fitting pictured.

Its just a pipe thread it’s sealed with thread sealant.

I’ve become good at changing crank seals on my airplane. There is a tolerable amount of oil that I will put up with.  Checking the back of the flywheel line you did should verify it’s not a crank leak.  

-Matt

 

[PT20J]

I had an I0-360 that leaked quite a bit. It came out on the belly. The only time I got a mist on the windshield was the front crankshaft seal. They can be replaced with a tool that stretches them over the prop flange, but you have to take the prop off. It doesn't take much to make a noticeable film on the windshield.

[Ragsf15e]

 Any chance it’s prop grease?  Is there “oil” on prop blades from the hub?

Was oil pressure low because your oil was really hot?  Because that could be normal…

[Mooncharlie]

- The oil drop 1qt, and flight time was around 4hs, it's not common but the day was extremely hot and adding the oil spray it seems right.

- Case checked, no oil leaks and everything adjusted. The engine is only 300hs SMOH.

- No crank or prop seal leak, it's not grease, and flywheel completely dry.

@MB65E I think you can have a good point telling me that the pipe just have sealant. It appeared after the second flight of the day, which I don't recall if I did a prop RPM drop test but if i did, hot oil, hot day and engine prop can damage the seal? searching through the pictures, i found which maybe can be a thin hair of sealant around the oil leaking area, picture attached.

Should I use any kind of special sealant for that thread if that's the problem?

I will try engine on ground, envelop the pipe with some paper and plastic on the other side to be sure that from there oil is dripping.

Thanks!

Edited January 29, 2023 by Mooncharlie
orthography

[PT20J]

NPT fittings can be a pain. They are tapered threads that form an interference fit. They need to be tight enough to deform the threads slightly to seal, but there is no torque spec. Usually half to a full turn after they get tight is about right. It's kind of a feel thing. Angled fittings are especially difficult because you have to get them tight and clocked properly and you shouldn't back them up if you go too far because that relieves the stress on the threads and can cause them to leak. Here are a few tricks I've used.

1. If a fitting leaks, throw it away and start with a new one. Sometimes the threads just don't mate properly and fittings are inexpensive.

2. Use aluminum fittings rather than steel if possible. The aluminum deforms easier for a better interference fit and is less likely to crack the boss if overtightened. 

3. Aluminum fittings threaded into aluminum can gall. To prevent this use Armite LP-250 on the threads. It the best sealant I've found. It seals and lubricates the threads and it won't gall, seize or leak. It is available in small tubes from McMaster-Carr, but for some reason doesn't show up on their online catalog so you have to call them to order it.

Skip

[Ragsf15e]

1 hour ago, PT20J said:

NPT fittings can be a pain. They are tapered threads that form an interference fit. They need to be tight enough to deform the threads slightly to seal, but there is no torque spec. Usually half to a full turn after they get tight is about right. It's kind of a feel thing. Angled fittings are especially difficult because you have to get them tight and clocked properly and you shouldn't back them up if you go too far because that relieves the stress on the threads and can cause them to leak. Here are a few tricks I've used.

1. If a fitting leaks, throw it away and start with a new one. Sometimes the threads just don't mate properly and fittings are inexpensive.

2. Use aluminum fittings rather than steel if possible. The aluminum deforms easier for a better interference fit and is less likely to crack the boss if overtightened. 

3. Aluminum fittings threaded into aluminum can gall. To prevent this use Armite LP-250 on the threads. It the best sealant I've found. It seals and lubricates the threads and it won't gall, seize or leak. It is available in small tubes from McMaster-Carr, but for some reason doesn't show up on their online catalog so you have to call them to order it.

Skip

Using the sealant is key to get it really leak free.  I’m not good at this, but using it liberally and then cleaning up any excess after tightening has worked for me.

Honestly I’ve had some (minor) issues with tapered “jic” fittings too and haven’t been able to get them perfect.  I want “sealant” for them!

[Pinecone]

3 hours ago, PT20J said:

2. Use aluminum fittings rather than steel if possible. The aluminum deforms easier for a better interference fit and is less likely to crack the boss if overtightened. 

My engineer side says, What MORON would put a steel NPT plug in a cast aluminum boss.

If it gets overtightened, it WILL crack the boss.

[MB65E]

8 minutes ago, Pinecone said:

My engineer side says, What MORON would put a steel NPT plug in a cast aluminum boss.

If it gets overtightened, it WILL crack the boss.

-Until you have seen cracked AN aluminum fittings. I’ve seen cracked an fuel lines fittings. I try to use stainless fittings where ever possible. Just don’t crank them in. Aluminum galls and strips too. 

What do you think the stud threads are on the cylinders? Steel! 
 

-Matt

[Mooncharlie]

Got kind of lost with the answers, sorry for my amateur mechanic knowledge

 

I see the recommended path, if the oil is leaking through the pictured NPT is to replace the pipe end and use a sealant that possible will not leak, am I right?

 

Taking that way, can anybody guide with part numbers, or specific thread size and parts so I can buy all the replacement parts? 

 

Thanks!

Edited January 29, 2023 by Mooncharlie
Error

[Pinecone]

NPT a tapered.  Cylinder studs are not.

With NPT, since it is tapered, you are effectively driving a wedge.

[PT20J]

18 minutes ago, Pinecone said:

My engineer side says, What MORON would put a steel NPT plug in a cast aluminum boss.

If it gets overtightened, it WILL crack the boss.

I've seen it specified to prevent galling. JPI specifies steel fittings for the Floscan fuel flow transducers. Really, neither steel or aluminum will crack if they are not overtightened. Same for B nuts on flare fittings.

I've had the most trouble getting fuel fittings to seal because fuel wicks well and is a solvent. My Garmin fuel pressure transducer was installed by an A&P using EZ Turn and it leaked. I reinstalled it with Permatex 3 and it leaked. The IA at the museum suggested Armite -- said it never fails -- and it has been dry as a bone since. Armite is mostly lead in an oil based carrier so it lubricates the threads and fills any gaps and it's impervious to solvents.

Skip

[Ragsf15e]

53 minutes ago, PT20J said:

I've seen it specified to prevent galling. JPI specifies steel fittings for the Floscan fuel flow transducers. Really, neither steel or aluminum will crack if they are not overtightened. Same for B nuts on flare fittings.

I've had the most trouble getting fuel fittings to seal because fuel wicks well and is a solvent. My Garmin fuel pressure transducer was installed by an A&P using EZ Turn and it leaked. I reinstalled it with Permatex 3 and it leaked. The IA at the museum suggested Armite -- said it never fails -- and it has been dry as a bone since. Armite is mostly lead in an oil based carrier so it lubricates the threads and fills any gaps and it's impervious to solvents.

Skip

I wonder if other sealants failing or being dissolved has anything to do with those fluctuating fuel pressure sensors weve run into?

[PT20J]

1 minute ago, Ragsf15e said:

I wonder if other sealants failing or being dissolved has anything to do with those fluctuating fuel pressure sensors weve run into?

I don’t think so. I put a snubber on it and I cannot see much fluctuation now on the G3X display, but if I dump the data and look at it it’s still observable though very much reduced. I’m beginning to think that it was always there but just damped out by the old analog gauge. I didn’t notice it until I had the G3X installed, and there were no changes to the plumbing;  G3X and its transducer are all that was changed.

[Fly Boomer]

5 hours ago, PT20J said:

It is available in small tubes from McMaster-Carr, but for some reason doesn't show up on their online catalog so you have to call them to order it.

Never heard of these guys, but it looks like the right stuff.  Ignore the picture:

https://bonesteelaerospace.com/store/ols/products/armite-1001-mil-prf-680b-type-ii-hydrocarbon-based-rust-penetrant-5-gallon-pail

[jetdriven]

7 hours ago, PT20J said:

NPT fittings can be a pain. They are tapered threads that form an interference fit. They need to be tight enough to deform the threads slightly to seal, but there is no torque spec. Usually half to a full turn after they get tight is about right. It's kind of a feel thing. Angled fittings are especially difficult because you have to get them tight and clocked properly and you shouldn't back them up if you go too far because that relieves the stress on the threads and can cause them to leak. Here are a few tricks I've used.

1. If a fitting leaks, throw it away and start with a new one. Sometimes the threads just don't mate properly and fittings are inexpensive.

2. Use aluminum fittings rather than steel if possible. The aluminum deforms easier for a better interference fit and is less likely to crack the boss if overtightened. 

3. Aluminum fittings threaded into aluminum can gall. To prevent this use Armite LP-250 on the threads. It the best sealant I've found. It seals and lubricates the threads and it won't gall, seize or leak. It is available in small tubes from McMaster-Carr, but for some reason doesn't show up on their online catalog so you have to call them to order it.

Skip

This fitting is required to be steel by AD.  Put some fuel lube on it and call it a day. Don't use Teflon tape 

[Mooncharlie]

10 minutes ago, jetdriven said:

This fitting is required to be steel by AD.  Put some fuel lube on it and call it a day. Don't use Teflon tape 

You mean, loose the fitting, add new sealant and tiigthen again?

[MikeOH]

@Mooncharlie

Maybe I missed it, but did you ever verify (with a paper towel around the fitting) the magnitude of the leak?

From your photo I just can't imagine you're losing that much oil (not to mention a 10 psi drop in oil pressure) from that fitting to mist your cowling and windshield.

[Guest]

5 hours ago, Pinecone said:

My engineer side says, What MORON would put a steel NPT plug in a cast aluminum boss.

If it gets overtightened, it WILL crack the boss.

Never seen two aluminum pipe threads locked together?  Backing them off destroys one or both of them.  Steel into aluminum with adequate sealant is a better solution.

[Guest]

From the Lycoming direct drive overhaul manual, some useful torque values, pipe threads amongst them.

[PT20J]

Apparently, I'm not the only one that has had leaky NPT fittings. I once had a gas water heater replaced in my home and while watching the plumber connect the gas line, and always wanting to learn from those with more experience, I asked if he used Teflon tape or pipe dope. He said he used two wraps of tape AND pipe dope. I suggested that that seemed like overkill and he replied that he was tired of having to return to fix leaks.

[PT20J]

3 hours ago, Mooncharlie said:

You mean, loose the fitting, add new sealant and tiigthen again?

You will need to completely remove the fitting and clean the threads. Since it is steel, it is unlikely to be damaged. Coat it with sealant leaving the bottom two threads clean (I suggest Armite LP-250) and reinstall it. 

[Pinecone]

On 1/29/2023 at 4:22 PM, PT20J said:

I've seen it specified to prevent galling. JPI specifies steel fittings for the Floscan fuel flow transducers. Really, neither steel or aluminum will crack if they are not overtightened. Same for B nuts on flare fittings.

Then don't use NPT threads.  Just straight threads and an O ring or gasket.

Yes, but it only takes a bit too much.  And with the angled ones, what happens when it is properly tightened, the thing points the wrong way?