The topic of oil shear stability testing has come up before:
Inliners Tech Tips circa '17 the Street Commodores testing gives the highest marks to Royal Purple and Penrite.
For me the most interesting take away when comparing modern motor oils is the primary objective that seems to be at play: extra long service intervals - 7500 to 10,000 miles in some cases. What hobby car is subject to such treatment?
Through the years the chemists have been trying to engineer oil additive packages that last longer and longer.
However, the chemistry in the zinc phosphate compounds used in motor oils reveal that the most effective ones are the least thermally stable - causing them to be used up (primarily at the edges of the compression rings). This leads to the need for a service interval built around zinc phosphate depletion - not oil cleanliness.
Taking us back to the old adage - "the best oil for your hobby car is fresh clean oil . . ."
