New oil "leak"?

[MikeOH]

I've owned my '70 M20F for three years and it has never dripped any fluids.

After the last three flights, when I have returned to the hangar a few days later, there has been a small amount of oil under the drain tubes aft of the nose gear on the pilot's side.  It's more than a few drops, but NOT what I would call a puddle.  I'm not sure which tube it is dripping from.  I believe one is from the fuel pump, but it's oil, not fuel.  It may be the drain from the oil/air separator...but, I think there is a third drain?

I don't like unexplained changes, so hoping for ideas on what could be going on?

Thanks!

[carusoam]

Oil from a tube... is the case vent most often...

• Too much oil in the case... and it wants to get out...
• Too much blow by... foaming causes the oil to get to the vent...
• lots of T/Os and landings, and the related higher AOA... cause the oil to move towards the back of the case, and closer to the vent hole... high power also causes some interesting affects of higher ICPs and related blow by...

If you have blow by occurring... the oil will get dark black and dirty... and will smell like exhaust...

The oil drips will be pretty dark as well...

Hopefully, this isn’t it... 

Good luck with the hunt,

-a-

 

[PT20J]

Tubes on mine are sniffle valve, fuel pump drain, crankcase breather, and vacuum pump outlet. The first two are smaller diameter than the last two. If oil is coming out the fuel pump drain, it could indicate a bad diaphragm.

Skip

[Owen M20F]

On my 67F the crank case drain is right above my pilots side cowl flap and i get some drips out of there as well, trying to diagnose my drips as well

[jamesm]

The third tube that you mentioned is i am guessing the battery box vent tube I think it might be 1/2". Oil breather I believe it's 5/8" od tube. As Skip has mentioned the other hose/tube which may or may  not have a short rubber hose is for excess fuel.

[Ragsf15e]

Mike, definitely important to identify exactly what tube.  The ~1/2” tube is the breather.  You normally will see oil out of that and it’s ok.  Maybe if you have an oil/air separator you don’t have much and it increased?  The rest of us without separators normally have some drips there and mist from that tube coats the belly during flight. Amount of oil out that tube depends on how much blow by, how full you keep the oil, patterns vs cruise, etc.

If it’s not that tube, @PT20J laid out the others.  Two ~1/8” diameter tubes (mine are attached) are the sniffle drain and fuel pump drain.  Shouldn’t get oil out those, but a failing mech fuel pump will drip oil there.  Further aft there’s also a drain (mine is blue) for the fuel selector sump.  There’s another in the same area for the electric pump.  Both of those are aft of cowl flaps.

Also, oil goes everywhere in there.  You might want to open up the cowl and poke around to see if a leak is showing up seeping down there.  Common leaks are oil return lines just below the cylinders, rocker box gaskets, and gaskets around all your accessories (mags, vac, governor).  It doesn’t take much oil to look real bad.

[PT20J]

I just replaced my sump quick drain the leaked a drop or two.

[Ragsf15e]

2 minutes ago, PT20J said:

I just replaced my sump quick drain the leaked a drop or two.

Ahh yes, that’s a common leak I forgot... oil quick drain is a good place to look for a drip!

[jaylw314]

9 hours ago, jamesm said:

The third tube that you mentioned is i am guessing the battery box vent tube I think it might be 1/2". Oil breather I believe it's 5/8" od tube. As Skip has mentioned the other hose/tube which may or may  not have a short rubber hose is for excess fuel.

The battery box vents in the J are in the rear fuselage right under the battery.

[MikeOH]

17 hours ago, jamesm said:

The third tube that you mentioned is i am guessing the battery box vent tube I think it might be 1/2". Oil breather I believe it's 5/8" od tube. As Skip has mentioned the other hose/tube which may or may  not have a short rubber hose is for excess fuel.

My battery and drain tube are way back, aft of the cabin.

[MikeOH]

8 hours ago, PT20J said:

I just replaced my sump quick drain the leaked a drop or two.

I recently changed my oil, so that is a great suggestion!

[MikeOH]

Sniffle valve was the one I couldn't think of.  Not sure I understand what it's for/how it works, and if it would drip oil?

My vague understanding is that it is a one-way check valve to the bottom of the intake manifold to drain fuel out, but seals off due to engine vacuum when the engine is running.  If that is correct, dripping oil doesn't sound too good!

[MikeOH]

8 hours ago, Ragsf15e said:

Mike, definitely important to identify exactly what tube.  The ~1/2” tube is the breather.  You normally will see oil out of that and it’s ok.  Maybe if you have an oil/air separator you don’t have much and it increased?  The rest of us without separators normally have some drips there and mist from that tube coats the belly during flight. Amount of oil out that tube depends on how much blow by, how full you keep the oil, patterns vs cruise, etc.

If it’s not that tube, @PT20J laid out the others.  Two ~1/8” diameter tubes (mine are attached) are the sniffle drain and fuel pump drain.  Shouldn’t get oil out those, but a failing mech fuel pump will drip oil there.  Further aft there’s also a drain (mine is blue) for the fuel selector sump.  There’s another in the same area for the electric pump.  Both of those are aft of cowl flaps.

Also, oil goes everywhere in there.  You might want to open up the cowl and poke around to see if a leak is showing up seeping down there.  Common leaks are oil return lines just below the cylinders, rocker box gaskets, and gaskets around all your accessories (mags, vac, governor).  It doesn’t take much oil to look real bad.

Thanks.  Yes, I have an oil-air separator which has done a good job of keeping the belly clean, and never previously dripped.  Not sure what can even go wrong; they don't have any moving parts!

I think just looking around with the cheek cowl removed is a great suggestion.

[Hank]

I just keep a cheap drip pan from the auto section of wally world behind the nose wheel to take care of those annoying post-flight drips. Used to keep kitty litter on it so the wind wouldn't blow it around, now I keep a piece of scrap metal from the work trash pile on it.

[MikeOH]

1 minute ago, Hank said:

I just keep a cheap drip pan from the auto section of wally world behind the nose wheel to take care of those annoying post-flight drips. Used to keep kitty litter on it so the wind wouldn't blow it around, now I keep a piece of scrap metal from the work trash pile on it.

I guess I've just been lucky.  I have NEVER had any drip of any kind up until now.

[carusoam]

Sniffle valve is at the end of the fuel injector drains...

FIs under certain conditions have excess fuel running out of them...  usually a start-up issue... 

If oil is getting into this line... it’s possible, but something unusual is happening to allow it...

The sniffle valve is a one way valve that has a plastic ball in an elbow and a pin keeping it from escaping... find the small  elbow with a pin through it, and you have found the sniffle valve... the Mooney/Lycoming sniffle valve is not all that complicated... the Continental one is more purpose built...

The intake system is near the valve train... if you have a worn intake valve... you might see oil and fuel come out in the same place...  

PP thoughts only, not a mechanic...

Best regards,

-a-

[Hank]

Just now, MikeOH said:

I guess I've just been lucky.  I have NEVER had any drip of any kind up until now.

Hang on, Mike! I've been typing on the tablet, pictures are on the phone!

[Ragsf15e]

51 minutes ago, MikeOH said:

Sniffle valve was the one I couldn't think of.  Not sure I understand what it's for/how it works, and if it would drip oil?

My vague understanding is that it is a one-way check valve to the bottom of the intake manifold to drain fuel out, but seals off due to engine vacuum when the engine is running.  If that is correct, dripping oil doesn't sound too good!

You described it perfectly.  And no, it shouldn’t drip oil...