I think there is a reason for being cautious about putting the return line into the engine, but that's not it.  The gunk that shows up in the separator is the very same stuff that is in the crankcase, so there isn't much reason to be afraid to put it back in.  The reason it looks bad is that after cooling, the moisture condenses and is visible.  In the crankcase the heat will boil off the water.  I think the reason to be cautious is that the pressure in the separator could, under some conditions, be lower than the crankcase pressure, and in that case oil could be "pumped" from the engine into the separator and potentially overboard.  So you have to be careful to make sure the oil drain is above any oil level, preventing solid oil from being driven overboard.

That being said, I would like to add a separator to my Lycoming, but I can't sort out the claims of all the units being sold.  Is there a "better" one - or one that actually works?

Gary Casey

I just bought an Andair Oil Separator from ACS.  According to a video clip
on Andair's site, these are being used by Cirrus and Cessna.

I haven't installed it yet because, despite the fact that ACS shows the
condenser trap on the pic, it must be ordered separately.  That is ordered.

Seems that the current thinking is NOT to drain that crap back into the
engine (acidic and emulsified with water).

Gordon