Just musing because I am not much of a technical person. What happens if you mix oils? Will they mix totally or perhaps keep separate properties. As a simple example if you mix a straight 80 with a straight 100 do you end up with a thorough mix that is 90 grade viscosity? What happens when you mix straight oils and multigrade? So many questions around this!
https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2011-01_all-about-oil.pdf local copy
Mike Busch has also issued a lot of other material on the topic, such as webinars etc.
I think all oils in common use in piston GA today can be safely mixed and you do get the, ahem, mixture of properties.
It’s mostly a matter of removing unknown variables. You can mix mogas and avgas also, but if the engine starts behaving “strange”, we all know for a fact what caused it 
That article in #02 doesn’t appear to discuss mixing of oils.
