One thing you may consider if you want to stretch out the useful life of your oil, try changing the oil filter more often than the oil. especially when using high quality synthetic oils. My brother worked for a large truck fleet operator that used Mobile One and never changed the oil. just the filters and top off. of coerce they pulled oil samples as well but the bottom line is they had trucks with over a million miles before pulling them out of service. In the interest honesty I don't know what the filter change interval was but this is just an option or suggestion for you to ponder.