I grew up on Phillips Trop-Artic 10W30, Ford and 2500 mile oil changes when one could buy a case (24 quarts) for $12 following Dad and Grandpa. In that day a motor with 60K was a trader and one with 100K...well...those were walk by cars/trucks. Thing is Dad and his brothers were not having much trouble getting three times that much mileage of an FE based Ford. 239 Flatheads went 600K to a million. I saw the internals of some of those motors when dad would drop a pan for an oil pump. Impressive. Unlike me, Dad likes to drive fast. Even at 90 years young 85 is his slow lane.
Boy did things change after 1970. The heat of the first generation SMOG motors was an oil killer. Thing was there wasn't ready access to synthetics yet and the ones that were, problematic and oil changes sooner than 2500? Oil prices were creeping up and motor life was again just average with 100K being a walk by.
When I got out on my own and started refining I gained access to a whole new world. Refineries have some pretty impressive laboratories. Oil and Fuel. I had a front row seat. Did two three year stints in Research on TDA's. Now there are some lab rats that would make MIT blush. Should too. Head Rats in charge of the cheese had multiple Doctorates from places like MIT, CSM & Oxford and with a much larger bank roll than any University. I got to see this stuff at the molecular level. Everyone's stuff.
Well retired a decade now and as fast as things change
Conventional oils use to have some serious differences in their base, that is ash, sulfur and wax content. You could have given me a Pennzoil Well back then and I wouldn't have run it in a lawnmower. Better living through chemistry they say and today those issues are nothing but lingering memories used best by marketing types and old wives. Entire sections of plants built to remove and standardize products. And yet the best of the best are still ground crudes with their inherent limitations. Add packages have not progressed as far as some would like to believe. Same basic chemicals are being used today that were used 40 years ago. Variance is mainly in concentration and packagers specific selection.
Major advancements in oil have come with synthetics. Even synthesized crudes such as Group III's that are just H2 full and finely cut are a good bump up but POA's and Esters are lightyear jumps.
Today the problem isn't knowing what a good oil is or even how often to change it. The problem is getting these LIARS to tell you what's in the bottle and no sir, SYNTHETIC doesn't tell you spit because these LIARS have corrupted the technical language to the point the word hasn't a meaning that is definite nor reliable.