Remove Air Oil Sep?

[Ragsf15e]

Hello,

My 252 has a 300 hour engine (with new cylinders) and it’s apparently always had a good bit of oil out the breather.  I ve been able to minimize it by running it only between 5-5.5qts of oil at start, but even with just 5.5qts, it spits a reasonable amount out.  My mechanic and I cleaned both the breather and air oil separator with no change.  I’m reading on BT that some people do better with no air oil separator at all?  Has anyone tried this before in a K?  What changes occurred?  Is it legal?

Thanks for any thoughts!

[Z W]

Mine used to do the exact same thing. Cleaning the air oil separator out is ultimately what fixed it for me, but before that, I changed the gasket on the oil filler cap. The working theory was that maybe pressurized cooling air that was supposed to be coming in on top of the engine and forced down through the cylinders was coming in under the oil cap and pressurizing the crankcase, which might prevent oil from draining back into the engine from the separator. The gasket I took out was cork, had seen better days, and came out in pieces. The new one was AMS silicone and costs $7:

https://www.aircraftspruce.com/catalog/eppages/gasket08-13778.php

I seem to remember maybe replacing an O-ring on the top of the dip stick as well but am not 100% sure on that. I put a nice new coat of paint on both the cap and dipstick end while I had them off.

Can't answer your question directly but at least inspecting your gasket would be a good idea. Maybe it didn't get replaced at overhaul.

[Ragsf15e]

4 hours ago, Z W said:

Mine used to do the exact same thing. Cleaning the air oil separator out is ultimately what fixed it for me, but before that, I changed the gasket on the oil filler cap. The working theory was that maybe pressurized cooling air that was supposed to be coming in on top of the engine and forced down through the cylinders was coming in under the oil cap and pressurizing the crankcase, which might prevent oil from draining back into the engine from the separator. The gasket I took out was cork, had seen better days, and came out in pieces. The new one was AMS silicone and costs $7:

https://www.aircraftspruce.com/catalog/eppages/gasket08-13778.php

I seem to remember maybe replacing an O-ring on the top of the dip stick as well but am not 100% sure on that. I put a nice new coat of paint on both the cap and dipstick end while I had them off.

Can't answer your question directly but at least inspecting your gasket would be a good idea. Maybe it didn't get replaced at overhaul.

Yeah, I tried the filler gasket as well initially but didn’t notice a difference. I haven’t tried the dipstick though.  I might look into that.

What level do you keep your oil?

Ill be interested if someone has tried it without the separator.

[Fix]

Never had any problem with oil coming out of the breather tube in an excessive way or high oil burn.
I wanted to have fresh o-rings and gaskets so I changed both the gasket in the filler cap and the quite dry/worn o-ring at dip stick.

I like to have much oil in my engine, at every oil change I add 7.5 qts and camguard.
After first flight I have just above 7 qts. (Get different reading depending on if oilstick loop is pointing forward or backward.)
When I have around  6qts, I'll add 1 qts.

Used Aeroshell 100 Plus in summer and Aeroshell 80 in Winter, but now changed to Philips X/C 20W50 so I can have same type of oil both summer/winter.

My Oil separator is the original that came from factory.

[Ragsf15e]

1 hour ago, Fix said:

Never had any problem with oil coming out of the breather tube in an excessive way or high oil burn.
I wanted to have fresh o-rings and gaskets so I changed both the gasket in the filler cap and the quite dry/worn o-ring at dip stick.

I like to have much oil in my engine, at every oil change I add 7.5 qts and camguard.
After first flight I have just above 7 qts. (Get different reading depending on if oilstick loop is pointing forward or backward.)
When I have around  6qts, I'll add 1 qts.

Used Aeroshell 100 Plus in summer and Aeroshell 80 in Winter, but now changed to Philips X/C 20W50 so I can have same type of oil both summer/winter.

My Oil separator is the original that came from factory.

I’ll do the dipstick gasket too but don’t have high hopes.  Mine will make a mess from tip to tail on a 3 hour flight if I put 7 in, you’re lucky!  At 5.5, it still puts some out and extends down the one piece belly after 4 or 5 hours, but burns only 1 qt/10 hours.

[Z W]

19 hours ago, Ragsf15e said:

Yeah, I tried the filler gasket as well initially but didn’t notice a difference. I haven’t tried the dipstick though.  I might look into that.

What level do you keep your oil?

Ill be interested if someone has tried it without the separator.

I now keep it at 7. Add a quart when it gets to 6, which is usually after 6-8 hours of flight.

[geoffb]

Rags,

Mine will throw oil when I fly high at higher power settings.  Breather and all hoses are clear.    The separator on mine drains back via the filler tube.  I’ve suspected that no oil flows back to the sump while the engine is operating at higher power as the crankcase pressure is higher and gravity isn’t enough.  Once the level in that tiny separator gets up to the top of the vent tube, it’s going over board.  Oil in the separator drains back at shutdown.  Compare the volume of an air wolf to ours.

just my musing on the subject.

[Ragsf15e]

3 hours ago, geoffb said:

Rags,

Mine will throw oil when I fly high at higher power settings.  Breather and all hoses are clear.    The separator on mine drains back via the filler tube.  I’ve suspected that no oil flows back to the sump while the engine is operating at higher power as the crankcase pressure is higher and gravity isn’t enough.  Once the level in that tiny separator gets up to the top of the vent tube, it’s going over board.  Oil in the separator drains back at shutdown.  Compare the volume of an air wolf to ours.

just my musing on the subject.

Those are good thoughts, thanks.  Mine does seem to have some crankcase pressure even though it’s only about 300 hours on a oh engine with new cylinders, so your theory does make sense.  I typically cruise at 65% power which could be enough to keep it pressurized and not draining.  The oil separator on ours is tiny, you’re right.  
I had noticed that it puts out more on longer flights, but I just figured it was because it was a longer time…

thanks,

Drew

[PeteMc]

On 4/4/2026 at 7:43 PM, Ragsf15e said:

I ve been able to minimize it by running it only between 5-5.5qts of oil at start, but even with just 5.5qts, it spits a reasonable amount out.  

I'm good at 7 (out of 8) quarts for my TSIO-360.  For me if I get oil out of the breather tube with only 7qts it probably means I've been doing a lot of training with a lot of power changes.  Or...  I've descended from a high altitude with a fair amount of power. 

Easy fix for the descent is a trick I picked up from John Deakin right after I got my plane.  He suggested I start whining way far out for a Pilot Discretion descent and then just go down at about 2-300 ft/min.  Theory is you regain some of that energy you lost climbing to altitude by a long descent and taking advantage of gravity. 

 

[Ragsf15e]

24 minutes ago, PeteMc said:

I'm good at 7 (out of 8) quarts for my TSIO-360.  For me if I get oil out of the breather tube with only 7qts it probably means I've been doing a lot of training with a lot of power changes.  Or...  I've descended from a high altitude with a fair amount of power. 

Easy fix for the descent is a trick I picked up from John Deakin right after I got my plane.  He suggested I start whining way far out for a Pilot Discretion descent and then just go down at about 2-300 ft/min.  Theory is you regain some of that energy you lost climbing to altitude by a long descent and taking advantage of gravity. 

 

Pete, does yours have the air oil separator on it?  It does seem there are several people who can fly ~7 qts.  If I do that, I’ve got oil shmooz all the way to the tail.  5-5.5 qts, very little.  I haven’t noticed a pattern yet in how I fly (high power, low power, long duration, etc) that changes it, but @geoffb  had some interesting thoughts about duration.  I’m mostly curious why mine appears to blow out oil more easily than others.  The simple answer would normally be high blowby / crankcase pressure, but it’s a relatively new engine?

Thanks, Drew

[PeteMc]

3 minutes ago, Ragsf15e said:

Pete, does yours have the air oil separator on it?

Yes, mounted fairly high on the firewall.  Maybe location has a lot to do with it, where is yours located?

 

[Ragsf15e]

3 minutes ago, PeteMc said:

Yes, mounted fairly high on the firewall.  Maybe location has a lot to do with it, where is yours located?

 

Mine is attached to the back of the metal baffle, just aft of the oil filler tube.  Seems high up.  Drains back to the base of the filler tube (small drain back through the metal baffle).

[N201MKTurbo]

The air oil separator is connected to the crankcase and should be at crankcase pressure. If the oil won’t drain because of a pressure differential, reducing the size of the exhaust hose should raise the pressure inside the separator and allow the oil to drain.