In article ,
Mike O'Malley wrote:

That still didn't make me feel better when I put that quart of 60 weight oil
in with the 15W50 when it was 15F outside. Man, did THAT ever take a long
time to pour. In hindsight, maybe running a quart low for the 30 minute
flight would have been a better idea? Well, it was only 1 quart out of
10...

Oil sumps are sized to allow maximum duration flights at maximum oil
burn without getting below the minimum quantity needed for safe operation.
The IO-540 requires some tiny amount (2.75qt sticks in my mind, but I
don't know if that includes the oil cooler and filter volume) but holds
up to 12qt. It will blow out most anything above about 10qt. The
Lycoming formula for maximum burn works out to be on the order of 1qt/hr.
So if you get 6-7 hours of endurance that would allow you to start at
10-12qt and end up in a safe (but low!) range.

So if your engine is one quart low, and it's not burning oil very fast,
you probably don't need to add any.

--
Ben Jackson

http://www.ben.com/