Jeff Bost

Jeff Bost

Member
Gentlemen,

Here are a few pics I snapped today of my crankcase breather line. I’ve gone from 7 to 4 qts in 13 hrs, with most being blown overboard. I realize I overfilled at the oil change but I’m concerned at my oil use. I went over the engine pretty well this morning and found no real leaks. A little oil at the bottom of the dipstick tube. I thought maybe I’m getting a vacuum at the breather and drawing oil out. I’d appreciate any ideas. Thanks,

Jeff
 

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Jeff Bost said:
What’s your best guess on how to fix it? Thanks, Jeff
Click to expand...

Install the breather IACW the plans -- see OP-27 (attached)

Screenshot 2024-08-30 at 5.25.09 PM.png

The exit of the breather tube is positioned immediately above the left hand exhaust pipe and is pointed forward. There are also a series of slots cut into the tube to let it "breathe" should the exit become blocked due to icing or other.

Here's another picture of the breather positioning:


IMG_2742.jpeg
 
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bjdecker said:
Install the breather IACW the plans -- see OP-27 (attached)

View attachment 69502

The exit of the breather tube is positioned immediately above the left hand exhaust pipe and is pointed forward. There are also a series of slots cut into the tube to let it "breathe" should the exit become blocked due to icing or other.

Here's another picture of the breather positioning:


View attachment 69503
Click to expand...
bjdecker said:
Install the breather IACW the plans -- see OP-27 (attached)

View attachment 69502

The exit of the breather tube is positioned immediately above the left hand exhaust pipe and is pointed forward. There are also a series of slots cut into the tube to let it "breathe" should the exit become blocked due to icing or other.

Here's another picture of the breather positioning:


View attachment 69503
Click to expand...

Bryan....this is very helpful. Thanks! I new this should be hard tube and not rubber hose like mine. I'll try and find someone that can help me correct this. Thanks again, Jeff
 
Jeff Bost said:
Bryan....this is very helpful. Thanks! I new this should be hard tube and not rubber hose like mine. I'll try and find someone that can help me correct this. Thanks again, Jeff
Click to expand...
For what it's worth, you can use rubber tube, just make sure its MIL-DTL-6000D type, 3/4" or 5/8" ID, which ever is appropriate to the size of the breather fitting on the case. Then route it down to just above the exhaust pipe, insert a section of aluminum tubing in the end (see second picture), put an angle on it and you should be good to go.
 
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bjdecker said:
For what it's worth, you can use rubber tube, just make sure its MIL-DTL-6000D type, 3/4" or 5/8" ID, which ever is appropriate to the size of the breather fitting on the case. Then route it down to just above the exhaust pipe, insert a section of aluminum tubing in the end (see second picture), put an angle on it and you should be good to go.

Your current installation has the breather sitting up a bit too high relative to the cowl exit. I agree with @rocketman1988 - you're probably getting some "suck" right there.
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Brian…..just to be clear, my airplane is a 6A. Don’t know if the setup is different on a 7. Jeff
 
When convenient, I‘d check compression on new cylinders, #3 #4 I think you said. You have confidence/documented break in on those? I run 6qts, top when at 5qts. Just some thoughts.
 
rocketman1988 said:
It’s a good bet that you are getting a vacuum drawn on that breather…
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Ok, I got $10 says no. Show me your measurements.

Point is, let's not propagate beliefs without data to support them.

In a general sense, there is no significant vacuum in a standard cowl exit. Not enough velocity, and anyway, static pressure prior to the plane of the exit is higher than freestream pressure. There may be some small local areas in the immediate exit wake with pressure lower than freestream static, but they are unlikely to be stable.

Too bad, because crankcase pressure below freestream static is desirable. I run a significant vacuum on the breather (3 to 3.5" Hg in cruise), on purpose. Marshall Murray (Sky Dynamics) has been building case evacuation into his exhaust systems for years (1" at 1500 to 3" Hg at 2700). One user measured the popular Anti-Splat clamp-on at a little over 1". Race engine applications use a vacuum pump to pull as much as 15". Cars have had a PCV system since 1967. None of these significantly increase oil loss. Reduced density means less ability to carry aerosol droplets.
 
BH1166 said:
When convenient, I‘d check compression on new cylinders, #3 #4 I think you said. You have confidence/documented break in on those? I run 6qts, top when at 5qts. Just some thoughts.
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Butch. Prior owner ran it hard with mineral for over 10 hours. We check compressions at prebuy with low to mid 70’s result. With that I went back to Phillips XC which I prefer and run in two other airplanes.

The dipstick on this O-360 had a series of notches and no numbers. I plan to calibrate at next oil change to verify marks. Last change we added 7, and wish I’d added 6. Jeff
 
DanH said:
Ok, I got $10 says no. Show me your measurements.

Point is, let's not propagate beliefs without data to support them.

In a general sense, there is no significant vacuum in a standard cowl exit. Not enough velocity, and anyway, static pressure prior to the plane of the exit is higher than freestream pressure. There may be some small local areas in the immediate exit wake with pressure lower than freestream static, but they are unlikely to be stable.

Too bad, because crankcase pressure below freestream static is desirable. I run a significant vacuum on the breather (3 to 3.5" Hg in cruise), on purpose. Marshall Murray (Sky Dynamics) has been building case evacuation into his exhaust systems for years (1" at 1500 to 3" Hg at 2700). One user measured the popular Anti-Splat clamp-on at a little over 1". Race engine applications use a vacuum pump to pull as much as 15". Cars have had a PCV system since 1967. None of these significantly increase oil loss. Reduced density means less ability to carry aerosol droplets.
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What do you do with the oil from the breather, Dan? Do you return it to the case, like the anti splat system does? Or do you collect it in a can and routinely dump it? Obviously, returning it to the case would show very little loss over time, certainly much less than dumping it overboard.

I'd like to see your data on the amount of oil collected from the breather with a static breather tube versus that tube with an aft facing 45 degree bevel in the cowl air exit stream, and that same breather in the free stream outside of the cowl.

Like you said, "...let's not propagate beliefs without data to support them."

Not looking for an argument; honestly curious about the data.
 
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Mine was like post 5.

I had minor leaks indicating a pressuized crankcase and a bit of consumption.

Now I am vertical, 45 degree bevel aft, about halfway between firewall bottom and top of lower cowl- but aft enough where the cowl ends.

There should be a bit of vacuum on mine. Engine does not seep and 1 qt per 25 hour consumption on steel jugs.
 
moosepileit said:
Mine was like post 5.

I had minor leaks indicating a pressuized crankcase and a bit of consumption.

Now I am vertical, 45 degree bevel aft, about halfway between firewall bottom and top of lower cowl- but aft enough where the cowl ends.

There should be a bit of vacuum on mine. Engine does not seep and 1 qt per 25 hour consumption on steel jugs.
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Thanks. Would love to see a photo. Jeff
 
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