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  #1  
Old 06-04-2022, 11:14 AM
Bavafa Bavafa is online now
 
Join Date: Oct 2007
Location: Sacramento, CA
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Default Automotive catch can for oil separator

I was wondering if there is any possible issue with installing an automotive style catch can as an oil separator. They are far less pricey. I am much less interested in returning the oil to the crankcase but to keep the belly clean.
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  #2  
Old 06-04-2022, 12:07 PM
gasman gasman is offline
 
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Any container that does not restrict air flow will work. Many use the fancy aluminum containers that high end energy drinks come in. The print can be sanded off. A piece of course scotchbrite to help remove the oil from the air will help.... Don't over do it. Check it often until you get a pattern.
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  #3  
Old 06-04-2022, 12:13 PM
Ralph Inkster Ralph Inkster is offline
 
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Location: Calgary, Alberta
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As long as it 'breaths' well & is cleaned out regularly, shouldn't be a problem.
I once saw an old plane with a Budweiser can dangling from the engine mount...
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  #4  
Old 06-05-2022, 09:06 AM
DSmith DSmith is offline
 
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The only caution I would add is the aircraft engine has a lot more blowby than an auto engine so the hoses, fittings and can would need to be larger to handle the volume.
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  #5  
Old 06-05-2022, 10:47 AM
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Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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I use the simple air/oil separator from ACS:
https://www.aircraftspruce.com/catal...ilbreather.php

The breather line extends down to just above the exhaust pipe. The 1/4” oil drain line goes to a repurposed Brasso or tap oil can mounted on the engine mount. I typically get 2-3 ounces in the can at each oil change - and non on the belly.

The photo shows where I mounted the separator on the firewall. Note the yellow cap is where the breather line goes.

Carl
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  #6  
Old 06-05-2022, 09:02 PM
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gmcjetpilot gmcjetpilot is offline
 
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Quote:
Originally Posted by Bavafa View Post
I was wondering if there is any possible issue with installing an automotive style catch can as an oil separator. They are far less pricey. I am much less interested in returning the oil to the crankcase but to keep the belly clean.
1) YOU DO NOT want that oil coming back to your engine. It is full of acid, moisture (more on that later) and crud.

2) You can lessen the oil by routing the end of the breather tube (metal) over and near your HOT exhaust at firewall near cowl exit air. This burns it off. YOU WILL NEVER have 100% clean belly as you have exhaust and engine oil drops into cowl. IT ALL BLOWS BACK AT 200MPH.

3) Cut slots in the breather tube (in the plans) so air flowing past end of tube does not cause suction or venturi action and draw out MORE oil causing excessive loss of oil. Also in cold weather in theory it will keep water from freezing in breather line.

4) Having ZERO catch can saves weight, and money. No catch can is cheaper and lighter than having a catch can.

5) What comes out of your engine is a by product of combustion and blows-by piston that makes it into your crankcase and oil. Also the oil is being beat to death and there is oil mist everywhere, some of that you do want to collect on the inside of engine case and drain back into sump (so you do NOT want too much savaging by vent tube). However if you block the vent it can cause excess crank case pressure and blow your crank's main seal out. That is bad.

6) What is a catch can? The theory is this: The mix of water, acid, oil air goes to magic catch can. I say magic because some of the commercial ones marketed for GA certified planes make some outrageous and false claims at worst. At best it's marketing hype that is silly. So this mess goes into the separator. There are two outlets. One is "clean air" in theory and the other is liquid, in theory clan oil which in theory you could return to engine. Where is all the H2O? In theory it is clean water and goes out with the clean air. HA HA HA HA. No. I had of those silver cans that mounted on the firewall on my RV4 for 1000 hours. The stuff it separated out I sent to a little plastic catch bottle. It was a milky degusting sludge with foam on top. The volume was not much. It would fill up 6 ounces between oil change. It filled faster cross country at high power and recall winter. No surprise high power continuously makes more blow by. I guess it was good and did not go on belly. I think a lot of it would burn off anyway as I describe above. Winter the catch bottle filled a lot faster but it was mostly water. Was it worth it? Yeah no. If you listen to the different brands and styles they are the greatest....

7) Those catch cans for cars are designed to keep blow by going back into engine induction (PCV positive crankcase ventilation) and oil in suspension deposits on valve. With Fuel injection unlike a carb you don't have all the goodness of fuel washing the valves with some port or direct injectors. Some of the oil catch cans are machined designs are clever and pretty. Two issue is weight and size (internal tube and airflow). When they machine them they may be chunky. Cars don't care about ounces. Also cars have very little blow by with tight tolerances common for water cooled engines. So it may be sized for very little air flow. Our Lyc is blowing many inches of Hg into the crank at high power. I think there are many articles about how they work for the intended car purposes. The jury is out. How they work in a plane? READ ON....

8) Hey make your own. There are many plans to make them. Try it and test it but DO NOT block or suck crank down below ambient. The way to test that is a using an AS indicator connected by a hose, connected to the oil dipstick tube (temporarily) with a custom cap and hose fitting. How do you test it?

https://www.csobeech.com/files/TCM-SB-M89-9.pdf

This is hard to follow but you use an old analog airspeed indicator with pitot and static air. You make an adapter where oil dipstick goes to attach a hose fitting to connect a vinyl hose to cockpit and pitot side of AS indicator. You run up and fly without the dipstick temporarily. There is always some positive pressure so you will see airspeed. The static port on A/S indicator is left disconnected or better tied into ships static. You are not looking for absolute numbers just relative. BTW this is a Continental service test. I don't recall Lyc having this test, at least officially. It works the same however. Lyc relies only on leak down compression test. That is fine. However that would not show a blocked vent or one acting like a venturi THIS IS NOT A LEAK DOWN COMPRESSION TEST but you can get good information. If your crankcase pressure is high, you could have excessive blow by due to piston ring issue. A leak down compression test on the ground will likely tell the tale. If it is high it could also be a blocked crank vent. ANY CAN you add, adds resistance to air flow out engineand thus higher crank pressure. This if excessive will blow your engine crank seal, Your windscreen will awash with oil. The other thing this will tell you is TOO LOW crank case pressure from the vent acting like a Venturi and sucking air out. This can lead to spectacular oil consumption il going overboard out vent. This is experimental so have fun and learn. Be aware the simple vent or catch can can cause serious issues if not installed and sized correctly.

Advice forget the can follow van's plans.
If you have a tight engine (minimal blow-by) and make your breather exit right you will have good crank ventilation, burn off most of the goop. A LOT of belly deposits is from exhaust and any engine oil leaks that drip into lower cowl. If a Lycoming engine is not dripping a little oil it has no oil in it. Ha ha. Bottom line up to you. For liability reasons I can't advise it. Some people report Nirvana with catch cans. I think it is mostly they spend all that time and money so of course it is worth it. However later they take it off and they see little difference on the belly??
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Last edited by gmcjetpilot : 06-06-2022 at 08:17 AM.
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  #7  
Old 06-07-2022, 08:26 AM
Tmartin66 Tmartin66 is offline
 
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Location: Washington,Oklahoma
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Default Slots in breather tube (in plans)

George,

I went back and reviewed my plans in regards to the breather tube. My plans (RV-14) do not have any instructions in regards to cutting slots. I would like to know more about this so that I may make the proper modifications. Could you elaborate?
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  #8  
Old 06-07-2022, 08:41 AM
JoeLofton JoeLofton is offline
 
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A data point for air/oil separator output. I installed an AntiSplat separator on my RV-3 (O-320 150hp) and plumbed the return to a collector bottle. I collect about one ounce every 20 hours. Note that I run the engine at about the 6 quart level.

Made the collector from a 5-oz baby bottle with the nipple removed, fitted with a bulkhead fitting in a large aluminum washer that fits perfectly into the bottle opening, held in place by the bottle’s screw-on ring. Drilled a hole near the top of the bottle to equalize pressure.
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  #9  
Old 06-07-2022, 09:11 AM
Bavafa Bavafa is online now
 
Join Date: Oct 2007
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Thank you all for your input.

I ordered a catch can from Amazon and for the price, it seems nicely made.
https://www.amazon.com/dp/B09B1QMS8G...t_details&th=1

The only issue is that it is rather heavy (one pound) so I am strongly on fence for installing it.

This
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  #10  
Old 06-07-2022, 10:48 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Tmartin66 View Post
George,

I went back and reviewed my plans in regards to the breather tube. My plans (RV-14) do not have any instructions in regards to cutting slots. I would like to know more about this so that I may make the proper modifications. Could you elaborate?
There is no step in the plans for making a slot or whistle hole as it is sometimes called.

The whistle hole exists in the tube on many certified aircraft because they often have the vent tube end outside the cowl in the slip stream which does make it vulnerable to freezing.

If the RV plans are followed, the resulting installation has no risk of freezing and hasn't shown to have any tendency to induce a low pressure on the end of the tube.
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