DEAR EXPERTS
I WOULD LIKE TO KNOW THAT THE OIL MANUFACTURERS RECOMMENDATIONS FOR OCI WHETHER IT IS 5K or 50K OR MORE IS BASED ON WHAT?
IF IT IS BASED ON AS PER OEM OR IT IS BASED ON OIL DEPLETION? WHAT IS THE SET PARAMETERS FOR BOTH?
CAN ANY EXPERT FROM THE BOARD ANSWER IN DETAILS

THANKS IN ADVANCE

I'm not an expert but I'd imagine they simply test the oil and see what is reasonable? Using oil analysis and tear downs you can come up with a desirable drain interval. Oil quality, engine type, sump capacity and driving conditions all factor in to drain intervals.

Oil Life Monitors (OLM) found on todays cars do not measure wear, TBN nor any of the critical oil depletion points outside of some algorythms based on speed, engine run time etc. So therefore cannot be counted on to accuretly determine how much life is left in your oil. An Used Oil Analysis is the only way to determine a healthy OCI IMHO.