When I had my first Car, a TR4 in the mid '60's I became and still am very interested in engine lubrication. I am no engineer, but have read all I can since then on esp engine oils. Back then, there were no consumer synthetics, the first was Mobil 1, which in Europe failed in a lot of Porsche engines. Mulit-grade oils quickly sheared to a less viscous oil, and many people still preferred non-detergent oil. If you looked under an engine's valve cover with those oils, the springs and valves were absolutely covered with gunk.
Engine oils came in metal cans, and were labeled in three ways; I bought Wolf's Head oil, rated MS for "mostly severe" as there were oils rated for "less severe" operating. At gas stations one could buy unlabeled re-refined oil in glass jars cheaper. The usual manufacturer advice was to change the oil every three thousand miles, and the oil filter every other oil change. Plus the old adage that ten pounds of pressure per thousand RPM was sufficient, and probably was. Late 40's and mid '50's cars often did not even have oil filters, and if so, it was often an option, and was usually some sort of "by-pass" system. Amsoil advertised a by-pass filter canister which used a roll of toilet paper as the filter.
Spin-on filters came later, too. In the winter very cold temps in Lincoln, when I was a student at NU, if I was going to get to class in the morning I would go out several times in the night and start my car to warm the oil a little, and an hour before I had to leave, push some stereo cans under the sump, avoiding the oil drips. I doubt that did much, but my electric heater dipstick probably did, although pulling it and wiping it with my fingers to check my oil level sometimes left a long burn blister on my hand. In an manual shift car, with non-synthetic cold transmission oil, it was very difficult to shift until the oil changed from grease to oil after driving a bit. All cars leaked oil, some more than others.
Manufacture owner manuals had bar grafs showing what viscosity to use depending on the expected ambient temperatures. Consumer oil analysis simply did not exist, either. I and likely most others, had no qualms about draining our used oil into the nearest woods or drain, never considering the environmental consequences, but then too there was no way or place to properly recycle our used oil.
So.... all I can say is that it is best to use or not deviate far from the manufacturer's recommendation, and in the end, remember that "...oil is cheap, engines are expensive."
NAM VET