Treat oil leaks seriously

M

MMM

Guest
A story of complacency. Quite a few years ago we had a twin that was flying on a weekend at a very busy flight school/flying club. I was the mechanic and was working part-time so wasn't fully in the loop on everything. Pilots wanted me to check out one of the engines for having some oil on the cowling. All engines leak, but these Rotax 912 engines in particular were just always leaking a lot. Pretty low time engines that looked brand new, just leaked constantly.

Oil looked like as much as normal, told them to check oil level and if that was good it was okay, just a leaky engine. Unbeknownst to me that had just had some work done on it and a part was not clamped properly back on. Ended up getting a low oil pressure warning and they shut it down + declared emergency. Luckily it was a twin.

Ever since that day I make sure if any pilot says it's got too much oil, I pull the cowls off, check for leaks, and wash the aircraft. And if you are wondering, I was honest with that fact and they considered the problem with the improper maintenance done, but it definitely is something that fell on me at the end of the day.
 
Engines aren’t designed to leak. If they do then something is wrong. If a mechanic tells me it’s just a leaky engine, can’t tell me where the leak is coming from and does nothing more than check the oil level I think I would be finding another mechanic. You are lucky you didn’t kill someone with your complacency.
 
kmacht said:
Engines aren’t designed to leak. If they do then something is wrong. If a mechanic tells me it’s just a leaky engine, can’t tell me where the leak is coming from and does nothing more than check the oil level I think I would be finding another mechanic. You are lucky you didn’t kill someone with your complacency.
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We dealt with this past year in a O-320 that flies about 300hrs/yr. Small amount of oil on the cowling. Searched for that leak for 8+ months. Used dye in the oil, baby powder, you name it followed by 30+ min in the pattern.

Couldn’t find it, despite replacing all the oil return lines and oil cooler lines. Multiple very experienced A&Ps with engine overhaul experience tried every trick in the book.

Turns out the crack in the case was developing and as the case heated up on a cross country, there was enough expansion for a small amount (less than an ounce) to mist out, get caught in the airflow around the engine and make it’s way out of cowling.

Then, after a couple of back-to-back 3hr trips, I went out to pre-flight and the crack finally made it’s way to fully developed. About 3oz oil had seeped out, but it looked like a murder scene. Cleaned the engine and did the dye in the oil and the crack finally showed up.


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In hindisght, the only thing we’d do different is order the exchange engine earlier, but there was no real smoking gun indicating the leak was getting worse, just a small streak on the cowling.
 
Now that I own a radial, this thread is kinda funny to me though it is really serious in context. My radial has an additional 4.5 gallons (yes gallons) of oil plus whatever is in the engine. Probably another gallon on the bottom of the plane. lol
 
My old lycoming O-235 "seeps" oil. I spent a very long time checking and replacing stuff to eliminate possible sources. It's been like this since I installed the engine 6 years and 600 hours ago. I think a small amount is from the sump gasket but at this time itn's not worth the time or effort to replace it. Also, it's not likely to complete eliminate every tiny drop of seepage.

At this point I know what is "normal" and what is not. I pull my cowl about every 10 hours or so to inspect the engine and oil seepage is part of that inspection. I do a thorough wipe down of any oil residue so I can keep track of the seepage. I use the term seepage because there are no "drops" of oil just a thin coating in certain specific areas.

I've heard mechanics say that any lycoming that has had the case apart will always leak some oil. There seems to be some truth in that.

If I had a rotax I would be more concerned. A fellow builder finished his RV about the same time as mine. You can still eat off his engine. I'd have to be really hungry to eat off of mine...
 
Pressure cowls make locating small oil leaks very difficult. Every situation is different. Use your judgement, and apparently be prepared to be judged.
 
Years ago after some maintenance on my Corvair conversion I found traces of oil on the belly after a short test flight. Thought it was a valve cover gasket or a pushrod o-ring, etc.

A fellow pilot suggested that since it was minimal that I should just fly it and keep an eye on it. I told him that if I knew where the leak was that might be a consideration but since I didn't know I had to find out.

At the end of the day it was a small leak coming from the oil cooler that I obvioulsy damaged during the work I was doing. I was relieved that I had found it and wondered what may have been the outcome if that small crack would have opened up in flight.

So the lesson is a good one. Engines should not leak ... although some do seep quite a bit! ;)
 
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Pinecone said:
And if a radial is NOT leaking something, something is wrong. :D
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But if it’s leaking much, something is wrong as well.

Unfortunately, as the OP noted, complacency sets in. Often because of trite comments that people take out of context as undeniable truth.
 
Not as bad as radials, but having a bunch of hours now behind the ole Conti O-300... if there's no oil under it, there's no oil in it...
 
kmacht said:
Engines aren’t designed to leak. If they do then something is wrong. If a mechanic tells me it’s just a leaky engine, can’t tell me where the leak is coming from and does nothing more than check the oil level I think I would be finding another mechanic. You are lucky you didn’t kill someone with your complacency.
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If they are recently overhauled, and properly maintained, they won't leak. But engines get old, their gaskets shrink and crack, the sealant on the case mating flanges ages and cracks, nitrile oil seals on the crank nose and vacuum pump drives (and alternator drives on the smaller Continentals) and tach drive all get old and lose their grip on the shafts and start leaking. Magneto gaskets get torn when mechanics reset the timing; one needs to take that mag off and replace the gasket to begin with. Otherwise the airplane will be back for that fix. On the Lycomings, the rocker box oil drain tubes are connected to nipples on the case by short sections of rubber hose that start leaking. They get very hot and are attacked by oil much hotter than what the oil temp gauges shows; that oil is coming from the head, after all. The Lycoming filler/dipstick tube comes loose when pilots overtighten that oil dipstick cap and the next guy has to use pliers or something to get it loose, torquing the whole tube and popping it loose at the bottom, against its lockwire. I used to take those out, install a new gasket with some Hi-Tack sealant and install them. That sealant would lock them in pretty good. And I showed the students and instructors that they didn't need to tighten that cap so much. Sometimes the crankcase breather tube cokes up with sludge formed from oil and water, and crankcase gases can't get out easily, pressurizing the case and forcing oil out of marginal areas. Checking that tube for free breathing is a Cessna inspection checklist item.

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The flight school engines rarely went past three years, so leaks were seldom a problem. Most common were those oil drain tube hoses, easily replaced if you know how and have the right tool. Checking the torques on crankcase sump hardware will sometimes find them coming loose due to gasket shrinkage.
 
Dan Thomas said:
If they are recently overhauled, and properly maintained, they won't leak. But engines get old, their gaskets shrink and crack, the sealant on the case mating flanges ages and cracks, nitrile oil seals on the crank nose and vacuum pump drives (and alternator drives on the smaller Continentals) and tach drive all get old and lose their grip on the shafts and start leaking. Magneto gaskets get torn when mechanics reset the timing; one needs to take that mag off and replace the gasket to begin with. Otherwise the airplane will be back for that fix. On the Lycomings, the rocker box oil drain tubes are connected to nipples on the case by short sections of rubber hose that start leaking. They get very hot and are attacked by oil much hotter than what the oil temp gauges shows; that oil is coming from the head, after all. The Lycoming filler/dipstick tube comes loose when pilots overtighten that oil dipstick cap and the next guy has to use pliers or something to get it loose, torquing the whole tube and popping it loose at the bottom, against its lockwire. I used to take those out, install a new gasket with some Hi-Tack sealant and install them. That sealant would lock them in pretty good. And I showed the students and instructors that they didn't need to tighten that cap so much. Sometimes the crankcase breather tube cokes up with sludge formed from oil and water, and crankcase gases can't get out easily, pressurizing the case and forcing oil out of marginal areas. Checking that tube for free breathing is a Cessna inspection checklist item.

View attachment 124243

The flight school engines rarely went past three years, so leaks were seldom a problem. Most common were those oil drain tube hoses, easily replaced if you know how and have the right tool. Checking the torques on crankcase sump hardware will sometimes find them coming loose due to gasket shrinkage.
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You made my point. If the engine is leaking then something is wrong. It doesn't mean that the airplane needs to be immediately grounded but the mechanic needs to at least inspect the engine and figure out what is leaking and why. From there they can figure out how important it is to fix the leak and how quickly it needs to be done.
 
Found oil (constant speed prop) slung onto the prop, cowling and windshield today - so I scrubbed the flight, called the club. Scary.
 
Hengelo said:
Found oil (constant speed prop) slung onto the prop, cowling and windshield today - so I scrubbed the flight, called the club. Scary.
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Any oil on the prop and it needs an overhaul, even a tiny bit. Least that's what I've always seen.
 
So there I was…

Ferrying a Pietenpol (a-65 engine) from Helena to Chicago. FIRST STOP oil leaking everywhere. Seller was a a&p IA who built the thing didn’t say anything about it. Called him, we agreed prolly just pushrod tubes. Lots of fuel stops, just keep it topped off…

Made the three day trip just fine, BUT…. Was a three inch crack in the engine case. An ounce more of cynicism woulda found it rather than biasing towards what I WANTED it to be.

Lesson learned.
 
A long, long tome ago I was flying cancelled checks in a 210 out of Bessemer, Al. Checks.?? what are those.?? Told ya it was a long time ago...

At the first stop I found oil down the right side of the plane. I wiped it off and looked for an oil leak. None found. I checked the oil level, same as before takeoff.

Next stop, same thing. No change in oil level. I wiped it off and continued.

Third stop, same thing.Again, no change in oil level. Wiped it clean and continued.

Got back to base about 6am, same thing, oil down the right side. Checked oil, no change in level. So I wrote it up in the plane log and showed it to the early mechanic.

The next day I talked to the mechanic that worked on it. There was a tiny crack in the oil cooler that let oil out the right side of the plane making a big mess. I mean every time I saw the oil down the side of the plane I expected the engine to be bone dry. It doesn't take much oil in the air stream to make a big, big mess.

My bag of luck emptied a little that night. That little crack could have turned into a very big crack and then the fun would have started...
 
This was an IO520F, being flown primarily over very cold water or mountains. I generally didn’t fly this airplane, but the pilot who usually did was sick and I ended up assigned to the aircraft. When I walked up to it I noticed some oil on the ground and leaking down the nosegear, I called the guy who usually flew it, asked if this was “normal” and he said yes it had been leaking for the last week or so he’d been flying it. I said well there’s nothing normal about a new oil leak, so we pulled the cowl and found this. The crack actually went all the way to the spine of the engine underneath the magnetos.

Nothing “normal” about an oil leak.


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DavidWhite said:
This was an IO520F, being flown primarily over very cold water or mountains. I generally didn’t fly this airplane, but the pilot who usually did was sick and I ended up assigned to the aircraft. When I walked up to it I noticed some oil on the ground and leaking down the nosegear, I called the guy who usually flew it, asked if this was “normal” and he said yes it had been leaking for the last week or so he’d been flying it. I said well there’s nothing normal about a new oil leak, so we pulled the cowl and found this. The crack actually went all the way to the spine of the engine underneath the magnetos.

Nothing “normal” about an oil leak.


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YIKES.!!
 
TCABM said:
We dealt with this past year in a O-320 that flies about 300hrs/yr. Small amount of oil on the cowling. Searched for that leak for 8+ months. Used dye in the oil, baby powder, you name it followed by 30+ min in the pattern.

Couldn’t find it, despite replacing all the oil return lines and oil cooler lines. Multiple very experienced A&Ps with engine overhaul experience tried every trick in the book.

Turns out the crack in the case was developing and as the case heated up on a cross country, there was enough expansion for a small amount (less than an ounce) to mist out, get caught in the airflow around the engine and make it’s way out of cowling.

Then, after a couple of back-to-back 3hr trips, I went out to pre-flight and the crack finally made it’s way to fully developed. About 3oz oil had seeped out, but it looked like a murder scene. Cleaned the engine and did the dye in the oil and the crack finally showed up.


ee988e9874cff62496b99165ce2f7b33.jpg


In hindisght, the only thing we’d do different is order the exchange engine earlier, but there was no real smoking gun indicating the leak was getting worse, just a small streak on the cowling.
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I'm currently stranded at KBQK due to a VERY similar sounding issue. Very little bit of oil streaking back along the cowling for the last year+ and the three A&Ps who have looked at it suggest a leaking crankshaft seal. They've told us it isn't a big deal, so we planned to have it replaced at annual later this month. After back to back 3 hour legs, I had oil all down the side of the fuselage. Sent our IA the picture and he said he no longer thinks it's a crankshaft seal, but probably something on the left side of the engine. It's not going anywhere until an A&P looks at it here, but it sounds eerily similar to your story.
 
flyingpreacher said:
I'm currently stranded at KBQK due to a VERY similar sounding issue. Very little bit of oil streaking back along the cowling for the last year+ and the three A&Ps who have looked at it suggest a leaking crankshaft seal. They've told us it isn't a big deal, so we planned to have it replaced at annual later this month. After back to back 3 hour legs, I had oil all down the side of the fuselage. Sent our IA the picture and he said he no longer thinks it's a crankshaft seal, but probably something on the left side of the engine. It's not going anywhere until an A&P looks at it here, but it sounds eerily similar to your story.
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Had a similar issue. In my case it was a leaking pushrod tube seal (crankcase-side). Monitored and deferred it until the prop had to come off for a hollow crankshaft inspection AD, since the nose bowl had to come off to pull that rocker cover.
 
AV8R_87 said:
Had a similar issue. In my case it was a leaking pushrod tube seal (crankcase-side). Monitored and deferred it until the prop had to come off for a hollow crankshaft inspection AD, since the nose bowl had to come off to pull that rocker cover.
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That's what we were doing - deferring until annual when we were going to take care of it. Not sure what we'll do now. I reckon we'll find out more tomorrow when the local A&P can look at it.
 
flyingpreacher said:
I'm currently stranded at KBQK due to a VERY similar sounding issue…
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There’s only a handful of places a leak can develop. What we hypothesize is that the longer cross countries were allowing the case and the oil to heat up enough to seep through and then get caught in the air flow around the engine before being expelled. These longer durations at higher temps and power were allowing the crack to slowly expand before it became detectable when cold/troubleshooting.

As I mentioned, we troubleshot ours for close to a year before we found the smoking gun, but it was a lucky and catastrophic find. We had planned to order a new engine anyways, but kind of got lulled into let’s trace the leak.

Given lead times, if you’re planning on an exchange, I’d pull the trigger now.
 
TCABM said:
There’s only a handful of places a leak can develop. What we hypothesize is that the longer cross countries were allowing the case and the oil to heat up enough to seep through and then get caught in the air flow around the engine before being expelled. These longer durations at higher temps and power were allowing the crack to slowly expand before it became detectable when cold/troubleshooting.

As I mentioned, we troubleshot ours for close to a year before we found the smoking gun, but it was a lucky and catastrophic find. We had planned to order a new engine anyways, but kind of got lulled into let’s trace the leak.

Given lead times, if you’re planning on an exchange, I’d pull the trigger now.
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So it turned out that the crankshaft seal was so loose it could be wiggled with a finger. There was NO sealant around the seal. It has been replaced and sealed and we are on our way again tomorrow!
 
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