I red somebody said changing interval for synthetic oil is 65k-70 k and I hope it was joke. First of all I would never use miles to change the oil but only hours.
Why ? It is so simple to explain. Imagine two truck following each other for a months but one is idling non stop because it is too hot or too cold and other one has APU. So after a month "following each other" they will have same milage but one idling 10 hours a day would have 300 working hours more and for these 300 hours that truck could make 15000 miles more than one with APU ( NO IDLING) ...300 HOURS MULTIPLE WITH 50 MPH =15 K MILES. So this math is unbeatable and if you add how idling is harsh on engines, especially on engines with DPF and DEF it makes picture even worse. So changing oil by miles is biggest mistake truckers make.....and changing oil after 60k or 70k is something I do not get it.