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  #1  
Old 02-28-2019, 07:02 PM
bob888 bob888 is offline
 
Join Date: Jul 2012
Location: Fresno, CA
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Default Breather tube extension

I have oil on the belly and probably more oil 'consumption' than ideal. I don't think it is due to blow by from the cylinders (only 220 hours) because the oil is not getting particularly dirty. I am wondering if the end of the breather tube is sitting in a relatively low pressure area in the lower cowl and whether extending it into the slipstream with a piece of radiator hose would help. Anyone able to speak to this?
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  #2  
Old 02-28-2019, 09:18 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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How much oil are you putting in? A number of people report that if you fill it over 10 the engine throws it out the breather.
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  #3  
Old 02-28-2019, 10:34 PM
lr172 lr172 is offline
 
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A perfectly running engine will put atomized oil into the air within the crankcase. Every engine has some amount of ring blow by and this excess air introduced into the case must be equalized/expelled. The air with the atomized oil suspended in it gets exhausted out the breather to equalize the excess pressure from the blow by and over time the atomized oil will stick to surfaces that air comes in contact with.

Years ago you used to see streaks of oil in the center of the road. This stopped when the EPA mandated PCV systems to prevent those vapors from entering the atmosphere. The OEM went to closed / recirc systems.

You want an air oil separator to reduce the oil left on the belly.

As bob mentioned, running to high of an oil level increases the cavitaion caused by the crank and this dramatically increases the amount of atomized oil created and why they blow out oil rapidly until the level is below the crank.

Placement of the hose won't change the amount of air and oil coming out of the engine.

Lycomings recommended fill level is not to accomodate what the engine needs, but instead to meet a standard for how much oil can be lost/consumed in a specific amount of run time without dropping below the minimum required, which is usually 2 quarts or less. If your consumptrion rates are above 1 qt in 10 hours, there is simply no need to put 8 quarts in a 4 cylinder engine.

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Last edited by lr172 : 02-28-2019 at 10:49 PM.
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  #4  
Old 03-01-2019, 05:42 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by bob888 View Post
I am wondering if the end of the breather tube is sitting in a relatively low pressure area in the lower cowl and whether extending it into the slipstream with a piece of radiator hose would help. Anyone able to speak to this?
Pressure within the lower cowl volume is equal to or higher than freestream pressure.
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  #5  
Old 03-01-2019, 06:18 AM
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Bill.Peyton Bill.Peyton is offline
 
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What oil level are you running? Most of us find that anything over 8 qts at oil change goes immediately to the belly. As Dan posted, breather tube extension is not the answer.
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  #6  
Old 03-01-2019, 06:21 AM
BillL BillL is offline
 
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Is there any kind of oil separator between the case and draft tube?
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  #7  
Old 03-03-2019, 06:17 PM
MConner MConner is offline
 
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Location: Snead Island, Florida
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Default Oil level

I have found my motor wants 8.5 quarts max. Anything over that will be thrown onto the belly.
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  #8  
Old 03-03-2019, 09:21 PM
bob888 bob888 is offline
 
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I fill to 8 qt and let it drop to 6.5 qt (this is a 540 engine). I'm afraid to run it below 6 qt. I'm having to add a qt every 5 hr or so, even at those levels.
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  #9  
Old 03-04-2019, 03:24 AM
MConner MConner is offline
 
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Location: Snead Island, Florida
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Quote:
Originally Posted by bob888 View Post
I fill to 8 qt and let it drop to 6.5 qt (this is a 540 engine). I'm afraid to run it below 6 qt. I'm having to add a qt every 5 hr or so, even at those levels.
I agree, I would not run it any lower. The happy oil level will manifest itself in an hour flight. A quart every 5 hours is a little high but not alarming but I would be cautious and have a motor guru look it over.
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