First a little background
I was raised on a farm in Connecticut, when we bought our oil it came in glass jars, with a metal screw on lid & spout, like this..
We returned the empty jars to get more oil.
When more & more companies started making oil, One or 2 of the companies were located in Pennsylvania, Quaker State was one of them. If you were to mix or change oil, like go from Texaco Flying A Brand motor oil to Quaker State, or just mix the 2,
pretty quickly you would discover that the oil from Pennsylvania was not compatible with any other oil, it would gum up your engine with a yellowish snot like goo.
I don't know if they still have Pennsylvania Crude Motor Oils made the same as in days of old.
I believe that this was where original DON'T MIX OILS came from
I still won't mix oils unless i am down a quart & can't get my normal brand
DUKEMAN, If it were me, those 2 cans would stay on the shelf in the garage, until a friend needed some oil & then it would be gone.
To this day, i will not mix oil brands
When i first bought my '09 Ram, Mobile oil had the Chrysler oil contract, about a year later, i believe Valvoline won the contract, then last year Shell won the contract. Shell Oil is Pennzoil for gas engines & Rotella for diesels.
That is when i changed to Mobile One synthetic & WIX oil filters