That is the eternal question. Factory interval is 7500 miles normal/3750 miles severe service. Oil was changed in March with QSUD 5w30 with a full can of MOS2 with a PureOne oil filter. Currently at 7200 miles. Usage is 75% highway 25% city right now. It can sit for two weeks at a time, then rack up plenty of miles for a trip. I have a 1500 mile round trip next week. I'll be pulling a sample after this trip for a UOA, at about 9K miles, hoping 10K is reasonable for this oil. Fighting the "fresh oil before a trip" bug real badly though.