For the past year, I have been draining my oil cooler when I change oil. You would be surprised how much drains overnight . . . about a 1.3 quarts! My lower oil cooler line is loosened and tightened just enough each time so that I do not damage the aluminum threads. It just seemed silly to me to add fresh clean oil to that much dirty oil (the oil in the oil cooler) in the system. Try it, you will be surprised!