I've got friends with OTR trucks and bypass systems with over 1/4 million miles without an oil change. That said, the bypass system has two different stations and when those filters are changed at filter change intervals I believe that's about 5-6 gallons of oil out of the total 15 or so gallons in the system every 25k or so. It's been several years since I looked into them and don't remember all the details now. They send in oil for analysis each time as well. It definitely saves a huge amount of oil compared to the not uncommon "change the oil every xK miles" that the oil/auto companies preached for so long.