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Old April 6th, 2012, 11:53 AM   #1
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Lycoming IO 360 oil leak

In a PA 28R 200. I believe it's a Lycoming IO 360 C1C.

I just noticed a small oil leak on the ground after a two hour flight. Looking up in to the front gear well, there is a small brass 90 degree fitting on the bottom of the engine near the oil drain plug which feeds a small (1/4 inch) oil line. I assume it's the oil line going to the prop control.

This fitting is retained by a brass lock nut. Oil was oozing out of the fitting, and the fitting was actually loose (not just turning loose, but wiggle loose) within the locknut. I threw a wrench on the brass locknut to see if it worked loose but it was tight. There must be some sort of o-ring or seal in there that blew out.

No oil appeared to come out in flight or there would be a big mess on the firewall and under the belly but I didn't observe any fresh oil other than in the immediate vicinity of the leak. I'm guessing that the fitting probably sealed itself in flight from the oil pressure, as it started leaking several minutes after shutdown. Or, it just happenend to fail as I was taxiing on the ground or as I was shutting down (seems unlikely but possible.) It's unclear how much oil was lost, there maybe an ounce or two on the ground. I checked the oil level, which was slighty over four quarts (I left with slightly under six quarts) but it was a warm engine and probably still draining down. Haven't got a chance to check the level cold again for comparison. Again, if I lost a quart and a half in flight I sure don't know where it went because I didn't see a mess on the engine or belly.

Is this a normal condition? If not is it an easy fix, e.g. pop the fitting off and replace a seal? The Lycoming site is frustrating as it does have a parts list but no diagrams. Yes I know an A&P needs to fix it but I just want to get a handle on what I'm in for.
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Old April 6th, 2012, 12:04 PM
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Re: Lycoming IO 360 oil leak

I think you may have found the sniffle valve. Got a picture?
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Old April 6th, 2012, 12:07 PM
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Re: Lycoming IO 360 oil leak

Just crawled under our arrow, it is indeed the induction drain. Shouldn't be oil draining out of that, but it is possible.
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Old April 6th, 2012, 12:28 PM
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Re: Lycoming IO 360 oil leak

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Originally Posted by Skylane81E View Post
I think you may have found the sniffle valve. Got a picture?
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Originally Posted by Skylane81E View Post
Just crawled under our arrow, it is indeed the induction drain. Shouldn't be oil draining out of that, but it is possible.
Isn't the sniffle there to allow somewhere for the expanding fuel vapors to go when a warm engine is sitting 'cooking off' fuel left in the lines?

If so, I would imagine oil coming out of that would be considered bad juju.
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Old April 6th, 2012, 12:36 PM
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Re: Lycoming IO 360 oil leak

Actually I just heard from the A&P that it was in fact a fuel line and not an oil line (go figure, who would expect a fuel line to go in to the crankcase) and the fitting in question was a pressure relief valve. What I thought was oil was actually congealed fuel goo of some sorts. So, I guess life is good.
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Old April 6th, 2012, 12:40 PM
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Re: Lycoming IO 360 oil leak

I was going to ask if it had a slightly blueish color.

The fuel line actually comes out of the induction system and drains off excess fuel.
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Old April 6th, 2012, 01:22 PM
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Re: Lycoming IO 360 oil leak

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Originally Posted by Skylane81E View Post
I was going to ask if it had a slightly blueish color.

The fuel line actually comes out of the induction system and drains off excess fuel.
Yes, it did, and there was some evidence of fuel boil off on the ground but the clearish blue goo didn't. Threw me for a loop.
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Old April 6th, 2012, 01:27 PM
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Re: Lycoming IO 360 oil leak

You have now learned something today, mission accomplished!
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Old April 6th, 2012, 02:14 PM
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Re: Lycoming IO 360 oil leak

Consider me skooled.
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Old April 6th, 2012, 03:23 PM
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Re: Lycoming IO 360 oil leak

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Originally Posted by Sac Arrow View Post
Consider me skooled.
It ain't a good day if I dont learn something new
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Old April 7th, 2012, 06:47 AM
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Re: Lycoming IO 360 oil leak

Just for future reference... you can get oil coming out of the manifold drain after shutdown if there is an oil leak around the exhaust or intake valves. As the engine idles it sucks oil and it can pool in the intake manifold. It then drains out of the manifold drain after shutdown.
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Old April 7th, 2012, 07:22 AM
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Re: Lycoming IO 360 oil leak

Welcome to the Zoo flying Ant.... and yes, this is correct, bad intake guides / worn valve stems will exhibit this exact scenerio..
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Old April 7th, 2012, 12:53 PM
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Re: Lycoming IO 360 oil leak

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Originally Posted by Flying Ant View Post
Just for future reference... you can get oil coming out of the manifold drain after shutdown if there is an oil leak around the exhaust or intake valves. As the engine idles it sucks oil and it can pool in the intake manifold. It then drains out of the manifold drain after shutdown.
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Welcome to the Zoo flying Ant.... and yes, this is correct, bad intake guides / worn valve stems will exhibit this exact scenerio..
Given that the engine doesn't even have 50 hours on it, I would hope that wouldn't be the case. But duly noted.
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