Rule number ONE: Junk oil is junk oil.
Rule number TWO: Never mix oils. Ever. You have no idea what the additive package of either oil is, and you mixing oils like that can add something from one oil that will affect the other oil. So STOP doing that. Mixing those oils may have made the additive package in both oils fail.
All engine oils have zinc. ALL OF THEM. The amount of zinc in the oil is less in “modern” oils and if you don’t have cats you shouldn’t be using ANY oil that says it’s just oil or semi synthetic oil.
I’m not going to get into oil groups in this post, but I need to correct an error I have made several times here on FABO.
Regardless of all that, any oil that is made of Group I or II (or both) is just obsolete.
Group III oils get called synthetic but they are not.
If you buy an oil that says semi synthetic it has to have Group I or II base oil (or both) plus some Group III oil, and it doesn’t have to be much Group III.
Oil is a case of spending more gets you a better product IN MOST CASES.
Buying **** oil off the shelf of a box store is a bad policy.
It’s not 1980 any more.