Mixing Brands

[CleanSump]

The answer to the actual question is that any API certified oil is miscible with any other API certified oil.

 

[pasadena_commut]

The answer to the actual question is that any API certified oil is miscible with any other API certified oil.

That is the answer when not destroying the catalytic converter is the goal. Although restricting it to API SM or higher oils would be prudent. (That last bit is directed at the "I found half an old jug of oil in the garage" folks.)

https://pqia.org/2021/04/15/motor-oils-for-classic-and-vintage-cars/

One could mix an API SP certified oil with something like Mobil 1 Racing oil, and that would be OK in vehicles without a catalytic converter (although maybe not an ideal viscosity). If one reads the data sheets on some of the high ZDDP oils they generally don't reveal why they should not be used in a street vehicle. For instance, here is the data sheet for Mobil 1 Racing oil:

https://www.mobil.com/en/lubricants...ts/mobil-1-racing-0w-30#lightbox-pdsdatasheet

it just says "...are advanced full synthetic motor oils designed specifically for racing engines and are not recommended for street use". Nowhere does it say why it isn't recommended. How does the racing engine differ from a high performance street engine? It might not at all! The difference that matters is the presence or absence of a catalytic converter. A person could read that document and assume incorrectly there is something technical about racing oil which would make it work poorly on the street, and while that is true in a way, "the high levels of ZDDP will destroy the catalytic converter" is probably not what most people would consider. That document says nothing about catalytic converters, by the way, nor does it say if the oil has an API rating or not. The bottle label also just says "not recommended for street use", and it says nothing about an API rating, presumably because it does not have one.

There are pictures of both sides of that bottle here:

https://www.summitracing.com/parts/mob-104145-1

Why not just say:

"This product should not be used in vehicles with catalytic converters"

?