If you really want to find out what is going on, do an Oil Change & drive it for ... say 5000 miles & take a sample & have it analyzed... If it comes back OK, drive it for ...oh, maybe 2000 more & repeat. This will give you a really good idea of what is happening in the engine & with the oil & you can tailor oil changes to your exact driving habits...For test kits, https://www.blackstone-labs.com/test...dard-analysis/ or stop by your local Heavy Duty Transport Truck Repair garage & ask for one from them... It can be very interesting... & post the results here so we can see. Mohammad did this with his Transmission & was able to determine it had a service before he bought the car (I Think,,,)