My notes from a member-side discussion are: Oil sump capacity for the IO-550N is 8qts; 5 usable at 16 degrees nose up and 4.5 usable at 10 degrees nose down. I don’t know your circumstances and operating technique. But, for reference, the most I see in my typical flying is 7-10 degrees nose up climb max.(initially) and 4-6 degrees max. nose down during approach to land, depending on the glide path I’m targeting.
I fly an SR 22 NA. The dipstick has been checked and the indicated oil level is accurate. I run 7 qts minimum before extended flights, and add oil when it gets down to 6, which takes a while. I only added 2 qts makeup oil on the last 25 hr oil run. And, for the last quart added, the oil level was only a hair below 6 qts cold prior to the last flight before the oil change. But, I won’t fly it under 6 qts.
The POH recommends 6 qts oil as a minimum in Section 8:
• CAUTION •
The engine should not be operated with less than six quarts of oil. Seven quarts (dipstick indication) is recommended for extended flights.
If your engine is venting oil excessively, there are multiple issues that should be checked for nonconformity and addressed.
Here is a link to an article written by Mike Busch that outlines in layman’s terms how to troubleshoot your issue. High Oil Consumption Of course, the Continental Maintenance Manual troubleshooting guide should always be consulted.
Good luck getting this resolved. As one example of risk, there was a CAPS pull in the UK resulting from bearing damage/ loss of engine power that the investigating body attributed to inadequate oil level in the sump. I’m not saying you’re headed for a CAPS pull. But, it’s risk you should consider when your SC is - allegedly - condoning your practice to run at a lower oil level than is recommended in the POH.