On the extended drain thing, even those that do suggest extended drain intervals, like Amsoil, only recommend their product up to 3 times the OEM recommended drain interval or 50,000 miles, or 600 hrs, whichever is shorter. That is something to consider when reaching out to longer intervals. Once you get past where the oil company itself may not back you, you are totally on your own if anything goes wrong. Delo will only claims its product will hold to 70,000 miles, and that is on the DD15. They do not state they will do that with other engines.

This is why I stated that my comfort level is 2x the OEM recommended drain interval for my Series 60, which is 30,000 miles and also bumping 600 hrs on average. That is even pressing it for me, as my comfort level is normally not more than 500 hrs. I suppose I could go 3x, but that is not in my comfort level. That all being said, even if the oil samples show oil ok at, say 100,000 miles, oil samples are just a basic snapshot. They do not reflect everything going on internally. There are some that have lost cams in ISX engines that the oil sample never showed coming. I am one of them. If a person is reaching out beyond what the oil company will back, you are on your own.

Just another thing to consider. If you know more than the oil company does, then I suggest you put a resume in with them and substantially increase your income level.