The guy that I bought the aircraft from wrote a list of some of the things about the aircraft that he gave me when I took ownership. Down on the list it said something about the engine being happy with a oil level of 6 quarts. Since it holds 12, I thought that must be a typo, that he really meant 9 quarts. Over the last 700 plus hours of operation, I have let the oil level slowly come down, trying to find a level where the breather stops blowing oil out, putting a film on the belly of the aircraft. I am now at 6 quarts and it is now pretty much stopped the film on the bottom. Being concerned about that level I contacted Lycoming and talked to a tech about it. He asked about temps and they are all normal. He said the the factory answer is a minimum of 2.75 quarts. He said that some IO-540's have a 8 quart sump, mine happens to be 12. He suggested talking with other IO-540 owners to find out what their experience has been, so here is my post. I am sure that others have had oil on the belly of the airplane, I just wonder how they got it to stop, if they did. I wondered if a different type of breather might help but the tech didn't think that would make a difference.