Mixing viscosities and or brands OK or NO?

[kschachn]

Back in the day, pre synthetics, there was and likely still is a military spec that
required mixability for oils that they purchase. As most brands, at least US brands,
wanted to sell to the government, they made their products accordingly.

That ASTM standard I linked says that it is similar to FED-STD-791/3470.1. FED-STD-791 is still current (apparently at revision D) and is an interesting read.

 

[pbm]

It's "safe" but I don't see the point

I recently changed the oil on my Escape's 2.5 Duratech which takes 5.7 quarts. I used a 5 qt. container of Mobil SS 5w20 and .75 quart of Mobil 1 0w30 because I didn't have another quart of SS 5w20. Mobil 1 has a different chemistry than SS but I doubt it will cause an issue in such a small amount....in other words I wouldn't mix them 50/50 and expect great results.

PS: Maybe I should have used .75 qt. of my older SN Valvoline synthetic since it used sodium in the additive package as Mobil SS did...

 

[Slow Car Sport Mode]

It's OK.

 

[nomas]

I've mixed oils in every configuration imaginable when I was younger . Never saw any issues .

 

[Dman]

Iv

My curiosity is because I'll end up with a bunch of containers with a quart or so of oil left in them from different brands.

Ive done this on more oil changes than not on my Mazda with 180k miles because I have multiple vehicles and I just buy whatever brand is cheap. I mix leftover oils of multiple weights and brands and throw it in the Mazda
It’s made it this far with never any apparent issue.

 

[CleanSump]

All of the manufacturers' websites FAQs or descriptions I've looked at state you can mix, but you won't get the advantages their brand gives you.