I've always been a 3k miles oci believer since i started driving and for all my cars (mainly 90s Mercedes diesels and various other gassers from that era). I've used all types of xW40, dino, semi and syn. I'm educating myself here and decided to switch to 5k miles oci using either 10W40 semi or 5W40 syn. While it's still tempting to drain it early, i feel that with today's oil quality, the 15k kms (9k miles) oil change that the Mercedes dealer recommends for my car can become a reality. I feel like 5k miles is still a waste of money and ressources but at the same time you guys can convince me to have the guts to extend intervals even further. How far would go with these types of oil : - 10W40 semi, API SN, ACEA A3/B4, MB229.3 (such as Shell HX7) - 5W40 synthetic, API SN, ACEA A3/B4, MB229.5 (such as Total Quartz 9000) The car is well maintained, 95k miles, 70% highway, 25% country roads, 5% city, running E85.