Running oil stains on nose gear door

[Lax291]

Are these stains normal? They seem to accumulate more over time but oil consumption is a quart every 10ish hours. Just a drip or two of oil on the hangar floor between flights and everything else is working well. I added a quart before my 2hr flight today to bring up the level to a total of 7qts and this is what it looked like after. Prior to the flight it had those stains but not as "heavy".

What do you guys think, is this cause for concern?  Thanks for your wisdom!

[Yetti]

lycomings like to mark their spot

[MikeOH]

I run mine at 6 qts.  You might try that instead of 7 and see if you get less 'staining'

[EricJ]

That's pretty normal, and is sometimes just oil that was spilled during the last oil change making it's way out the bottom of the cowl.   If it ever suddenly gets worse than normal, then that's something to pay attention to.

[Lax291]

Thanks guys, I'll experiment with running at 6 quarts. 

[Slick Nick]

I dunno, that dark streak in your first photo is coming from somewhere way ahead of the breather. And it’s black. Whenever I get oil on the gear door it’s brown and back past the breather. you need to pull the cowl and see what’s leaking. 

[201Steve]

the firewall is a funnel that leads directly to the nose gear assembly. Could be anything. Only way you’ll find it is to clean the engine up really good and then notice it before it spreads everywhere. it’s a constant battle. That looks like a normal amount of oil for a common leak. If your oil level is about the same, probably no real worry. A little bit goes a long way. However…. I hate oil leaks and I will try my best to find them over time, but I don’t obsess about them like I used to. Sometimes it takes a lotta tries before you can pin point. If you’re not comfortable tinkering, at least try to isolate the general area it begins to accumulate anfter cleaning and then relay the findings to your mechanic. 

[Lax291]

Wondering if this could be from my quick drain. I often notice a small drop of oil on the end of it. 

[MikeOH]

11 minutes ago, Lax291 said:

Wondering if this could be from my quick drain. I often notice a small drop of oil on the end of it. 

Yes, possible.  Mine occasionally will have that happen after an oil change.

I carefully (without pushing in on the quick drain!) push on the plastic tubing I use to drain.  Then with the other end of the tubing well above the level of the oil, I start blowing on the tube to put pressure in it, finally I'll open the the quick drain for a second and let it snap shut.  Repeat a couple of times.  That has always stopped the dripping for me.  I think a little piece of 'crud' gets on the sealing surface of the valve and blowing backwards dislodges it.

[mooney2201]

I have found that oil return lines cause this problem, Followed by valve cover gaskets

[MikeOH]

1 minute ago, mooney2201 said:

I have found that oil return lines cause this problem, Followed by valve cover gaskets

Yuup!  I have had both of those leak.

[mooney2201]

You probably still have one or more leaking...I've had my m20j for 29 years .you must completely degrease the engine..start with a pristine clean engine...you will find the leak..just take your time

 

[Pinecone]

And if you can't seem to find it, UV dye works wonders.

[M20Kid]

Did you fly through any clouds or rain?  I find whenever I fly in visible moisture, the "smoking" is heavier and longer.

[Lax291]

23 hours ago, M20Kid said:

Did you fly through any clouds or rain?  I find whenever I fly in visible moisture, the "smoking" is heavier and longer.

No clouds, or rain (just starting instrument now).  

[PT20J]

My '78 J did that. It's definitely a small leak in the engine compartment. In my case it was several.

[Jeff Uphoff]

On 12/2/2024 at 9:13 PM, Lax291 said:

Wondering if this could be from my quick drain. I often notice a small drop of oil on the end of it. 

My shop replaced my Ovation's quick drain last year after noticing a minor leak. Wasn't a big deal--$100ish part and an hour-something labor.

[A64Pilot]

Mine looks like that, on mine I think it’s a push rod tube leaking

One day I’ll do something about it, and I second the 6 qt recommendation.

Can be coming from the bottom of the filler tube too, lots of potential leaks

Edited December 7 by A64Pilot

[Lax291]

Just got back from a 5hr cross country and noticed oil drops coming out of this metal tube. Oil looked pretty clean and not all black like what was running along the nose gear door. Added a Quart about 7 hrs ago after about 10hrs on a fresh change. 

[PT20J]

It’s normal to have a few drops come out the breather tube after a flight. This is the source of the oil on the exhaust cavity behind the tube but not the source of the oil on the gear doors (which originate ahead of the tube).

[T. Peterson]

On 12/2/2024 at 8:13 PM, Lax291 said:

Wondering if this could be from my quick drain. I often notice a small drop of oil on the end of it. 

It could be from many different places. My leaking is worse than yours and I have had at least four different shops try to find it, including an MSC. I have had all the pushrod seals replaced twice, a complete hose kit installed and the thru-bolt seal replaced. The hose kit did make a difference but not near enough. Hundreds of dollars later I just decided to replace the engine. Don’t panic, you don’t have to replace your engine. My engine was old and sat idle for six years, sort of like the current owner .

[Grant_Waite]

10 hours ago, Lax291 said:

Just got back from a 5hr cross country and noticed oil drops coming out of this metal tube. Oil looked pretty clean and not all black like what was running along the nose gear door. Added a Quart about 7 hrs ago after about 10hrs on a fresh change. 

I don’t think anyone has mentioned it, but to me it looks more like something is rubbing. All my oil stains I ever get are much lighter even when the oil is used. The rubbing of any aluminum on aluminum will cause what some call “smoking” which creates a black very hard to clean up, wipe it and it smears type stuff. I know I’ve replaced the chafe tape in my gear doors like 3 times because of oil making the tape not stick. I got some tape from @Jetdriven and it sticks great but forgot what it was. I just did an oil change and got oil all over the place and it’s still sticking great. It almost looks like it’s coming from the piano hinges on the gear doors but mine doesn’t rub there. Just where the doors overlap on one another. I’d look in the nose wheel well and see what you can find. I’ve had crud come out of the lowest part of the bottom cowl, where the 2 camlocs go. If there’s no tape there, it can cause rubbing and airflow can make it blow on the doors and get all over the hinges. 

[Lax291]

I know I'm beating this horse but adding some more photos. I'm not too concerned as the oil loss appears to be within normal range. Spanned a few photos through the cowl flaps today. 

Edit: Photos got uploaded in random order.  From left cowl flap, photos 3, 4, 5.  The rest are from the right side. 

 

 

[Yetti]

The best way to see leaks is look at the engine for the big drops.    I found that the fitting on the drainback tube at the Cylinder Head was leaking.   The nut on the fitting was tight.   but the ferrel that is around the aluminum tube was loose just a little with the oil drip showing.     So I loosened it and moved the ferrel around and then got the fitting tractor tight.    Also the clamps on the hoses on the drain back tubes need to be tightened regularly.

[Vance Harral]

I hesitate to say this in public, but after posting and asking questions like this about the oil stains on our gear doors and exhaust tunnels for years, our long-standing mechanic finally said to me one day, "Son, you need to either overhaul the engine, or lower your standards."

Certain oil leaks that are benign from a safety perspective, simply cannot be fixed without maintenance that is just as likely to cause serious problems as it is to fix the annoyance of the oil leak.  In our case, the main source of the leaking oil is the gasket seal on the oil pan, which is quite long in the tooth.  This could definitely be addressed without an engine overhaul, but it would require removing the oil pan, which first requires removing the exhaust, which first requires removing the lower cowl, and so on.  All of that could generate more serious problems.  A bit of leaking comes from the rubber couplings on our oil drainback tubes, as @Yetti notes.  When this first started, we tightened the hose clamps a bit and got it to seal, but eventually the rubber got pretty brittle, and it's more or less impossible to keep it bone dry without replacing the couplings - which maybe can be done without removing exhaust and/or induction tubes, but it's a pain.  We have a couple of pushrod tubes that leak chronically at the seal near the cylinder head.  The gaskets have been replaced multiple times, but they continue to seep.  When we had cork valve cover gaskets, they'd start seeping after a year or two, though that's gotten better with the silicone gaskets.

Sometimes seeping oil comes from a blown main seal at the crankshaft.  We do check for this, and address it when found.  But it's not really a critical airworthiness issue, and the prop has to come off to address it.  One time the mechanic who removed the prop showed me how the previous mechanic to remove the prop botched the prop bolt safety wiring on re-installation.  

We do wash the engine at every annual, inspect for oil seeps at the crankcase seam and cylinder attach bolts, look for cracks in the case, etc.  More importantly, we try pretty hard to wipe the oil off after each flight, so that we're starting from a relatively clean state, and can check after the flight to see if the amount of oil on the gear doors and exhaust tunnel is "normal".

Bottom line, I've come to accept that while we'd all like a bone-dry engine, the design of the engines we fly isn't really conducive to staying dry through thousands of hours and dozens of years.  Most of the Lycoming/Continental engines I see in the shop and on the ramp leak some amount of oil - particularly flight school airplanes and those flown for hire.  For better or worse, I've abandoned the dream of a dry engine... at least until overhaul time.