Oil out breather - unlikely that it’s blowby

[Ragsf15e]

I’ll add pictures later this week when I go clean the belly, but here’s the story…

TSMOH - 220hours, 3 years 

Last Annual - April 2025

When I got my 252 in January, one of the first things I noticed was how much oil was on the belly after a flight. It wasn’t actually using much according to the dipstick, but the spray was from the breather tube all the way to the tip of the tail along the belly.  At first, I thought it was blow by, but then I realized the oil was still looking new after 25 hours since oil change and the compressions were all good at the annual in the 60s. Then I realized the oil cap was a little loose so I changed the O-ring on it and it seats nicely now. Finally, I thought I solved the problem when I realized that both the breather and the return line from the oil separator were routed down underneath the cowling to exit the engine compartment. Yes, the oil return line was not hooked up to return oil to the engine. My mechanic fixed that at the annual and cleaned out the oil separator.  
 

The next five hours of flying had a small amount of oil out the breather which I considered normal. Then this weekend I flew two ~3 hour XC legs and again I have a lot of oil out the breather. I would say it’s not as much as before the annual, but it goes from the breather tube all the way back below the avionics compartment.  The engine only uses about 1 quart every 10 hours.  When I left on my cross country this weekend, there were 6.5 quarts of oil in the engine. After the first three hour leg I checked and it still had more than six, so I didn’t add any. I’ve been trying to keep it right around six because lots of people say it will blow out more than that. Does anyone keep it below six?

From my reading, it seems that it could have something to do with a prop shaft seal or maybe the dipstick isn’t sealing right or maybe the breather or oil separator are clogged somehow? Or maybe pointing the wrong way? I have no idea how we should go about troubleshooting this. I really do not think it’s blow by from a cylinder.

My breather is bent near the exit and ziptied there to point directly aft.  Is that how others are?  My F model breather opened straight down.

I feel like I'm grasping at straws… any suggestions?

Thanks,

Drew

 

Edited Monday at 05:14 PM by Ragsf15e

[N201MKTurbo]

Do a compression check and listen at the oil fill.

[takair]

Where does the oil return line from the separator go now?  There seems to be a science to getting it right too.  If the routing allows oil to build up it becomes ineffective.  

[Ragsf15e]

47 minutes ago, takair said:

Where does the oil return line from the separator go now?  There seems to be a science to getting it right too.  If the routing allows oil to build up it becomes ineffective.  

There is a small tube on the bottom of the oil filler tube for the return line.  I’ve actually been thinking about this because routing that line has to go through the back baffle (filler tube is forward of the baffle, oil sep is aft), and my return line is in an inverted U shape right now stuffed through a hole with some other lines (maybe ignition wires?).  Almost has a “P” trap in it…

[Z W]

Mine used to blow out anything over 6 quarts. I would let it drop to near 5, then fill to 6. Oil pressures and temps were fine this way and the internet said it was OK to do. My POH says "Oil Capacity Minimum for Flight - 5 qts."

After cleaning out the air/oil separator and lines and replacing the oil cap gasket, that improved, and now it holds 8 pretty well, but seems to do best between 6 and 7, so I add a quart at 6, about once every 10 hours of flight.

All measurements here are described after the engine has sat off for 30+ minutes. If you take a reading right after landing you will be 1 quart lower than described.