11-30-2011 Ask Mike! Archive
What's the best air/oil separator for a Bonanza?

Mr. Thompson and Team AVSTARAir,

I can't get my classic Beechcraft in the air to fly her to your facilities just yet...so I'd like to engage you for an hour of advice.  I'll be more than eager to pay for an hour of "Mike's shop time" for an answer to my question.  Might I impose? 

I have a 1956 Bonanza, Model G35.  E225-8 engine.  I've just spent a year restoring/refurbishing this lady and I have an engine issue for which you've come most highly recommended.  Unfortunately, she's not exactly airworthy yet...so a flight from Santa Fe to Puyallup isn't in my cards just now.  Thus, I'm writing this request in advance of bring my aircraft to AVSTARAir for additional work. 

My issue is that my E225-8 does not have an air/oil separator on the breather.  At all.  The previous owner told me that he removed it because it wasn't working.  Hmmm....Okay...not sure I buy that, but I am a novice to classic Bo's.  Obviously, when I do get to fly this aircraft, I spend almost as much cleanup time on the plane's belly as I do flight time in the air.  My question is this:  What would be your recommendation on the most appropriate/effective air/oil separator to install to slow my overboard flow -- and where would an installation of that air/oil separator be most efficiently routed back into the engine?  If a separator is installed on the right side, say, would a return to the accessory case oil passage plug 1/8 Inch NPT (part number 2024 from TCM Illustrated Parts Catalog, page 18, Figure 10) be an intelligent consideration?

I would welcome your recommendation on this work and it would greatly reduce the stress on my AE/IA helping me make this addition.  I will certainly pay you for your energies in reply to my question.  If you'd like to speak with me directly for further clarification or if you have any questions, please feel free to call my mobile phone listed below.

Kindest Regards and Many Thanks In Advance,
Bobby C

Hi Bobby;

Airwolf makes the best A/O separator currently available.  This should do nicely for you, and yes, mount it on the aft side of the right rear baffle (not many places to choose from.  This does make battery R & R a bit more time consuming, if you have the original battery box.)  However, do not use the 1/8 NPT hole you are calling out (I believe you are calling reference number 9 from the IPC); that is a pressure oil port and you would rapidly fill the separator with oil.  Use the port reference number 11; that is a straight in to the cavity port as originally called out for the vacuum pump separator dump.

Of appropriate consideration is the placement of the overboard duct from the separator.  A number of them I have seen exit the cowl flap area; this can actually cause a venturi effect and draw out as much or more oil than you are experiencing.  Generally, I put the end of the duct about 2" above (and parallel to) the skin adjacent to the right-rear drag-link fitting on the keel.  You may need to play with exact placement a bit to fine tune your installation.

Best of luck to you and the G!
Mike