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"

?

 

[OVERKILL]

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"

?

Catalytic converters have been around a LOT longer than the current restrictions on phosphorous. This is made doubly amusing by the fact that Euro oils continued to have higher limits on phosphorous long after the API started capping it at 800ppm and even the C3 oils designed for GPF compatibility, devices that are MUCH more sensitive than traditional catalysts to contamination have a higher ceiling at 900ppm.

Also, if you are mixing a sump full of 760ppm phosphorous API SP oil with say one quart of Mobil 1 Racing, you'll end up with a total concentration of phosphorous at approximately what we see in your bog standard full-SAPS Euro lube.

 

[pasadena_commut]

I had a converter fail in the mid 90's in a 1988 Mazda 323 which was not burning oil or running poorly - very possibly from the phosphorus in the (relatively) high ZDDP oil of that era. I don't recall the mileage exactly, but it was I think somewhere between 125k and 150k at the time.

Think of phosphorus in cats as being like lead poisoning - the damage is cumulative but doesn't have to be acute. So a person (at least an adult) can consume lead somewhat above the recommended limit for a pretty long time without having any significant symptoms appear. Unfortunately, statistically a person doing that will accumulate cardiovascular, kidney, and other damage and eventually that will cause symptoms or even organ failure. So consuming lead is a bad idea even if one glass of lead contaminated water won't cause immediate catastrophic health issues. Pumping phosphorus into a catalytic converter is similar - the converter efficiency will slowly fall and it will eventually fail earlier than it would have had the phosphorus been avoided. Especially so if the car is burning a lot of oil, where a modern low ZDDP API oil can result in more phosphorus entering the converter than from a high ZDDP oil in a non-oil burning motor. (On top of whatever damage all the extra carbon does.)

Admittedly, like the lead damage scenario, if the car isn't going to last long for some other reason (rust from salted roads?) then the damage from the phosphorus may never reach the point where the car catalytic converter gets so bad that it throws a code.

I'm pretty sure that the current level of ZDDP in API rated oil is based on some "lifetime" calculation like "on average this will not destroy the converter for 200k miles", not, "this will not destroy the converter". Interesting that they were unable to switch over to some other chemical. Suggests that anything which binds tightly to engine metal for wear protection will also bind tightly to the catalytic metals in the converter and inactivate it.

 

[gfh77665]

I never go out of my way to mix. I do not think it makes anything better.

I will mix without hesitation if it helps use up some random, leftover quarts.

Never, ever, hurts a thing. Ever.