I had a Canton road racing pan and with the cooler and remote filter set up it held about 10 1/2 quarts. And yes,
oil does stay in the cooler and lines, but not enough to make any difference when you change the
oil. I left that old
oil in to give the new a little color as it was easier to see on the stick. And my pan was 9 quarts. I filled it before I put it on the car so I could see where the 9 quarts came to and that way I knew if my dip stick was reading correctly. Also the length of lines to and from the cooler and remote filters will make a difference. And remember the filter holds most of a quart when you put a new one on.
Ron