Breather tube

[PT20J]

Well, consumed oil has to leak out, get blown out or get burned up. Sounds like you don't have a leak and a lot isn't ending up on the belly. That leaves piston rings or valve guides. BTW, Lycoming will tell you that 3.5 hrs/qt is perfectly acceptable. It may be if it hasn't changed suddenly. But if it has changed a lot, I would investigate until I was confident I knew what was going on.

I bought a M20J that was burning about 2 hrs/qt. During prebuy, all cylinders had compressions in high seventies. The exhaust stack wasn't sooty. The cylinders still had cross hatch and no oil and the plugs were dry. The last oil analysis done shortly before purchase was normal and the filter was clean. It ran great and the oil burn was a bit of a mystery. But, the airplane hadn't flown much the last few years and I thought to run it a bit and see if it improved. It actually got to about 2.2 hrs/qt and was running great when we did the annual about 30 hours after purchase. At that point we found that #3 cylinder compression was 58/80 with air heard blowing into the crankcase. The filter had metal and the suction screen had a piece of a ring in it. We pulled the cylinder and found that the oil control ring had broken and taken out a chunk of piston skirt. So, I learned from that experience that they can be running great with a serious mechanical problem. Not sure how long it would have continued to run. The piston skirt was burned and so it was getting pretty hot.

Skip

[N811SS]

Quick question -->  Do you have a GEM?  If so, did it show high CHT or EGT on #3 before she went tits up?

[N811SS]

p.s. -- Why is number 3 always the problem child cylinder? 

[PT20J]

48 minutes ago, N811SS said:

Quick question -->  Do you have a GEM?  If so, did it show high CHT or EGT on #3 before she went tits up?

The airplane has an EDM 700. And I made a typo -- it was actually cylinder #2, left rear, that went bad. As I recall, the CHTs and EGTs on #2 were always pretty normal and within 20 degrees or so of the others. The EDM had a storage problem and wasn't recording data properly, so I don't have plots from that time period.

Skip

[Guest]

4 hours ago, PT20J said:

The airplane has an EDM 700. And I made a typo -- it was actually cylinder #2, left rear, that went bad. As I recall, the CHTs and EGTs on #2 were always pretty normal and within 20 degrees or so of the others. The EDM had a storage problem and wasn't recording data properly, so I don't have plots from that time period.

Skip

Skip,

Unless your J has a Continental engine, cylinder #2 would be the front left.  Cylinder #4 would be the left rear in a 4 cylinder Lycoming.

Clarence

[PT20J]

7 hours ago, M20Doc said:

Skip,

Unless your J has a Continental engine, cylinder #2 would be the front left.  Cylinder #4 would be the left rear in a 4 cylinder Lycoming.

Clarence

Clarence, you are absolutely right. I seem to have become dyslexic or something 

It was indeed #4. 

Fortunately, there are only 4 cylinders -- I was bound to get the right one sooner or later.

Skip

[carusoam]

So...

1) Oil showing up on a spark plug is not normal...

especially if you are trying to find out which cylinder is misbehaving...

Assuming for a moment that one is misbehaving...

That one would be the one to look closer at...

 

2) case venting...  it is important to have the proper length, diameter, ice / vent hole, bends...

This is important because there are so many variables involved...

There is one known solution for that engine, in that plane...

If yours is different, don’t be surprised if getting the right part installed properly is the solution to your challenge.

 

Finding a vent tube probably isn’t all that expensive... compared to pulling a cylinder off looking for broken rings...

Want to find a used Mooney/Lycoming vent tube?

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[carusoam]

Guy,

Does the vent hole have a particular shape to it? (Look like a whistle?)

Or is it just a straight hole? (Fuzzy memory only...)

Best regards,

-a-

[N811SS]

Hello All, here is my update -

By God, preliminary/premature results (i.e. after only 5 hours of flight time) do hint at a reduction in oil consumption since I installed the black extension tube (see photo from my original post).  Where I used to be a consistent 1qt each 3.5 hours I think I am now seeing about 1qt. every 4.5 hours.  Go figure!  Perhaps Carusoam is correct when he says: "...case venting --> It is important to have the proper length, diameter, ice / vent hole, bends...this is important because there are so many variables involved..."

Now my challenge is figuring out what is the optimal part for my particular aircraft.  I can't use history because this machine has had so many changes since it originally rolled off the assembly line over 53 years ago (i.e. 201 cowling, cowl flaps closure amount tweaked, powerflo exhaust, electronic ignition, stand-by vacuum, engine rebuilds, air/oil separator put-on then taken-off, etc.) .  I wish I could find specs on what Mooney says it should be for perhaps a "J" model.  I walk around the airport and try to take a peek at what other Mooneys have  installed and it seems there is no one consistent configuration.  I suspect the length of the tube is important because I could see where air pressure rushing out the bottom of a closed cowl flap would be greater and hence creating a low pressure environment.

Any advice?  What does your exit tube look like?  How far back does the exit pipe go? Does to extend beyond the end of the cowl flap?   I know this is not the most important thing in the world but would like to take my best shot at getting it as good as it can be.  

[carusoam]

Somebody accidentally captured one on their M20C...

Of course what you are looking for is most likely for an M20J...

As the most modified M20F is an M20J...

I was thinking of your quest when I wrote this response...

-a-

 

[Owen M20F]

On 1/2/2019 at 6:00 PM, Shadrach said:

Greetings all,

Where would be the best place to procure breather tube similar to the OEM part?  This is for a 1967 F model. Mine is so brittle that it's become challenging to R&R.  It likely started life as transparent, yellowish brown plastic. Years of service have turned it dark brown.

Does yours drop below the cowl flap or sit right above it? I’m having oil seeping out the breather excessively and think it’s a low pressure pulling it out 

[carusoam]

9 minutes ago, Owen M20F said:

Does yours drop below the cowl flap or sit right above it? I’m having oil seeping out the breather excessively and think it’s a low pressure pulling it out 

Somebody posted pics and lengths I believe...

There is also a breather hole aka whistle hole in the tube to keep the vacuum of air rushing by from sucking your oil out...

So.. check for the breather hole and how short the tube should be...

 

Also know there is a case pressure test in case blow by is the cause for your excess oil venting overboard...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Owen M20F]

7 hours ago, carusoam said:

Somebody posted pics and lengths I believe...

There is also a breather hole aka whistle hole in the tube to keep the vacuum of air rushing by from sucking your oil out...

So.. check for the breather hole and how short the tube should be...

 

Also know there is a case pressure test in case blow by is the cause for your excess oil venting overboard...

PP thoughts only, not a mechanic...

Best regards,

-a-

Yes I’m going to do the case pressure test. I have a hard time believing that’s the issue since i did 4 cylinders 70 hours ago

[N201MKTurbo]

https://www.aircraftspruce.com/catalog/appages/polyurethanetubing.php?clickkey=3763

I have a customer who uses this hose for fueling jet aircraft. C-210-A tubing. It lasts over 10 years full of jet fuel.

BTW, this is not what they have at the Home Depot.

[PT20J]

Aircraft breather tubes are a bit of a mystery to me. Autos (before the advent of positive crankcase ventilation in the 1960's) had a similar arrangement usually called a road draft tube that ran from the top of the crankcase to to a point beneath the car and was usually cut at an angle to create a low pressure area (draft) to suck out the unwanted gases from the crankcase. However, auto engines also have a means for fresh air to enter the crankcase (usually a hose from the air cleaner to the crankcase). Airplane engines seem to have the exit, but no inlet. Maybe it's just that the blowby is so much greater in looser tolerance air cooled engines that they don't need one. Anybody know? 

Skip

 

[EricJ]

3 hours ago, PT20J said:

Aircraft breather tubes are a bit of a mystery to me. Autos (before the advent of positive crankcase ventilation in the 1960's) had a similar arrangement usually called a road draft tube that ran from the top of the crankcase to to a point beneath the car and was usually cut at an angle to create a low pressure area (draft) to suck out the unwanted gases from the crankcase. However, auto engines also have a means for fresh air to enter the crankcase (usually a hose from the air cleaner to the crankcase). Airplane engines seem to have the exit, but no inlet. Maybe it's just that the blowby is so much greater in looser tolerance air cooled engines that they don't need one. Anybody know? 

Skip

 

It goes both ways through the breather.   If the pressure inside the case is less than ambient, it flows in, if more it flows out.

For the OP, my IA only allows Mil-6000 flexible hose if using flexible, which is fine to do.  Check with your IA to make sure they're good with signing off on whatever you decide to put in there, but flexible hose is certainly the easiest.  Mil-6000 is available at aicraft spruce and other places, and should be fine with any IA.  Only about the last 8-10" of mine are hard line, and I think that's just bent aluminum tubing.   I was thinking of making the hard line part of mine longer to make a more proper whistle vent (as mine is currently just cut into the Mil-6000 flexible hose, and once in a while it burps crap into the engine compartment).  Some raw stock and a tubing bender can form one to fit.

 

 

[Shadrach]

14 hours ago, Owen M20F said:

Does yours drop below the cowl flap or sit right above it? I’m having oil seeping out the breather excessively and think it’s a low pressure pulling it out 

IIRC, mine stops just below the firewall. So about even with the cowl flap in the closed position.  I’ll check this weekend.

[MikeOH]

5 hours ago, Shadrach said:

IIRC, mine stops just below the firewall. So about even with the cowl flap in the closed position.  I’ll check this weekend.

That's the way mine is on my '70 M20F

[PT20J]

6 hours ago, EricJ said:

It goes both ways through the breather.   If the pressure inside the case is less than ambient, it flows in, if more it flows out.

Maybe. But since the tube exits at a low pressure area, the crankcase pressure would have to be pretty low to suck air in. And, what would cause the low pressure? Blowby during compression, power, and exhaust strokes should all act to increase pressure. 
 

[EricJ]

20 minutes ago, PT20J said:

Maybe. But since the tube exits at a low pressure area, the crankcase pressure would have to be pretty low to suck air in. And, what would cause the low pressure? Blowby during compression, power, and exhaust strokes should all act to increase pressure. 
 

As long as the pressure in the case is equal or higher than ambient, or the pressure at the end of the breather, it'll flow out.   But as one descends into higher pressure, or reduces power, or lands or turns off the engine or whatever other factors apply, as soon as the gradient reverses the flow reverses.   This means that there's never a high differential between the case interior and the ambient pressure.   It doesn't really need fresh air in there.

 

 

[Martin S.]

On 3/28/2020 at 2:38 AM, N811SS said:

All good questions/responses.   Thanks.  To provide some more details:

Engine Background:

* Engine is an IO360-A1A (the original)
* Engine rebuild was 700 hours (about 7 years) ago.  Re-honed cylinder 2 & 4 at the 125 hour mark.  Replaced cylinder 3 at the 400 hour mark due to broken ring.  Re-honed cylinder 3 at the 500 hour mark again.  Through-out all of this, oil consumption has remained at 1 qtr every 3.5 hours.

* The oil gets dark (but not real bad) by 8 to 10 hours after a change....and that's considering that I keep adding a qrt each 3 to 4 hours.

* The belly on the left side (behind the breather tube) gets a little bit oily but nothing too bad.

* The engine compartment is perfectly clean (no oil drips anywhere).  Nor have I ever seen oil drips on the ground after parking. 

* Have done borescope many times and there is usually a little bit of oil on the bottom of cylinder 3 but nothing too bad according to the mechanic.  The hatching on the walls looks good to everyone and no signs of glazing.  The compression's are good in all 4 cylinders (76/78/78/77).  The bottom plug on cylinder 3 has a little bit of oil in it but I cant say the plug has every been fouled.  

* Its just weird, I keep feeding oil into this thing and it just disappears...I guess it is getting past the rings and burned in the exhaust...its quite the mystery.

 Crankcase Pressure (according to the mechanic):

 The only reason that the wind from the prop blowing past the exit port of the breather tube might be creating a negative pressure in the crankcase is because the mechanic hooked-up a manometer water tube to the dipstick filler.  He tried 1000, 1700, 2500 rpms and could not get a positive pressure in the crankcase!  He could hear the engine puffing past the rings but at full rpms the crankcase pressure was negative (3" of water in his tube)!  The top cowling was off but the bottom cowling was on.  I asked if he compared open cowl flap to closed cowl flap and he said no.  Then, he disconnected the black crankcase breather hose up near the accessory case and voila all of the sudden he could measure positive crankcase pressure at double the normal range.  He surmised that prop wash was creating a venturi effect on the breather tube.  I know that sounds like a stretch especially considering that tube is angle-cut such that the opening is facing backwards (see photo below) but I noticed that other Mooneys have the breather tube run toward the tail for about 5" .

 

...So here is what I did this afternoon.  I went and bought a small section of tubing from the auto-parts store with a 90 deg bend and clamped it on the existing (see below).  I am doubtful it is going to make a difference but I don't see the harm in giving it a try.  I will report back my findings. 

Here is just a Mooney photo i picked off the internet (its not my plane) showing the breather hose pointed aft:

 

 

Evening everybody,

Reviving his topic. Can somebody explain me what the small rubber tube in the above photo is for and where it comes from?

Thanks in advance,

Martin

[PT20J]

Either a sniffle or fuel pump drain.

[201Steve]

There are two lines on my io360. intake manifold sump drain(sniffle) and mechanical fuel pump drain- where fuel goes when the pump *diaphragm?* fails. 
 

 

[carusoam]

Summary….

 

The pic shows three tubes…

case vent… metal tube with a whistle hole in it to prevent blockage in freezing weather…

Intake drain, with the Sniffle valve in it… (modified elbow, check valve)

Fuel pump drain, that only leaks when a seal needs to be replaced…. Or a diaphragm ruptures…

Mooneys with a battery up front will have another drain for the battery case….

PP thoughts only,

-a-

[Martin S.]

Thanks everybody. Was already guessing it originates from the intake - but not sure.