I change mine about 75 passes, but I have a 10 qt system (9 qt Milodon SS pan, a Wix filter that holds just under 1 qt, a remote filter set up and external oil line). It is not unusal for me to make 20-some passes in a weekend. With oil, filter and additive, a change cost around $75 for me, plus getting rid of 10 qts used oil.
