I'm just throwing this out to add to the general conversation and maybe provoke a little alternative thinking on oil changes.
When I initially started working on CL&P equipment we used 10W40 conventional oil throughout the fleet which at the time probably numbered right around 10,000 pieces, including cars, trucks (up class
heavy equipment, and a variety of odd ball stuff related to the utility business like large (2000KW and up) generators, core borers, track machines etc.
At the time we changed the engine oil and filter every 30 days on small vehicles and every 90 days on large stuff. During that time which was over 10 years, we had virtually no oil related failures. Over the years we reexamined our service schedule and eventually arrived at schedule of changing the filters every 90 days and the oil once a year, regardless of mileage. We used full synthetic 20W40 Mobil Delvac 1, and we used it everything. During the 20 or so years that we used that schedule we had virtually no lubrication related failures.
Which method was right? I can't say. If anything our equipment was over maintained, oil was checked just about every time a vehicle was used, for certain it was checked every time the vehicle was fueled or came into the shop for any reason, even if it was just to replace a signal bulb, and the drivers knew that if the engine popped they'd be without "their" truck until it was fixed. So by no means would I consider the way we did things indicative of how anyone else should do them. But it does offer some indication of how good modern oils and engines can be.
I use full synthetic in my road bikes, and change it at the recommended intervals, which usually works out to 2-3 changes a year. In my
off road bikes I run conventional oil and change it after every hard ride or after three easy ones. My cars get full synthetic /high mileage and I change it every 5K. Again I'm not recommending any particular regime here, it's just what works for me.