First time to use forum. Put this message in "chat" forum. May not be the correct place. Posting again in maintenance forum.
Having issues with access oil on belly after a 30 - 45 minute flight. Compression checks are good. Latest attempt to solve the problem was to remove oil / air separator off wet vacuum pump. Cleaned oil / air separator with solvent, and compressed air. Was surprised to find that opening on oil / air separator return line to engine was very, very small. Never had this part off before. Could see where it would be easy to become clogged. After cleaning, drilled the opening to make it a little larger. Don't know if this helped or hurt. Any insight on this issue would be appreciated. Thank you.

Danny,

While your set up may be different, one of the common problems for Twins is 'overfilling' the oil. While the dipstick and capacity is 8 qt per engine, I keep them at 6 qt. Oil consumption is 15-25 hours per qt. Minimum is 2qt so still a nice safety margin. Don't know if this is your issue but if everything else is in good shape, thought I'd mention this.

Danny, when you say "compressions are good" can you share what your compressions are? I had a situation where compression on one cylinder dropped from 78 at previous check to 68 and I had slightly increased oil consumption. Many people, shops, and mechanics said - "hey it's still well within spec - just fly more and monitor".

That answer was not good enough for me or my IA. We determined air was leaking thru the rings on the compression check so we pulled the cylinder and found that one of the rings had broken! There's a longer story behind all this but I put on a freshly overhauled P010 Lycoming cylinder assembly (all my cylinders are P010).

I suspect your air oil separator or perhaps over filling as Pat indicated are the issue but you mentioned compression so I thought I'd ask. I agree with Pat that anything over 6qts tends to blow out. Also on the twins with the same amount of oil in both engines the oil on the dipstick will read about 1/2 qt higher on the left engine due to dipstick position on the left side and the dihedral in the wing (the oil pans are canted towards the fuselage). So I always expect to see left engine oil at 6.26qts and right engine oil at 5.75qts (approx). Since you refer to oil in the belly I assume you have a single.

- Charles

Thank you for your response. Been a Comanche owner for years, as well as ICS. Never used the forum. I've been missing out!
Response to comments. I'm aware of the "over filling issue". The 250 holds 12 quarts. Try to run around the 9 quart mark. Seems to work best.
Response to compression numbers. Lowest is 76 / 80. Highest is 79 / 80. All others are in between. Going to put the oil / air separator back on and fly the airplane. It was obviously clogged. Any comments on the very small opening on return line from oil / air separator back to engine. Can't find anyone who can tell me why it was designed this way. Most suggestions were to drill the opening and make it a little larger. I did. Don't know if that was a good or bad idea.
Thanks again for the comments.

Given those compressions (very good indeed) it does not sound like a ring problem. We have an Air Wolf Air-Oil separator in a Cirrus and we've had it clog before and cause a similar issue. Not sure what to say about the return line you reference other than to suggest you call Air Wolf and ask them (I've found their tech guys helpful). Our AirWolf unit has a 100hr ICA for cleaning and maintenance.

- Charles

PS - I LOVE these forums. Yes they are a GREAT resource for Comanche info. I have benefited greatly from them in sorting out issues on my bird.

The vent hole should be there to prevent a case over pressure in the event that the breather exit from the airsep freezes up. A standard breather line also has one commonly known as a whistle slot.

Zach - thanks that makes sense about the hole. You also (I think) answered another question I've always had.... What's that little slot at the top of the metal pipe that makes up the breather tube?... That's the "whistle slot" I take it?

Thanks,

- Charles