Mixing same brand oil with different viscosities

[roswell998]

Is there any problem with mixing 10-30W and 10-40W same brand (just different weight) oil or could there be incompatible additives?

I just happen to have enough of above for an oil change and wanted to change it tomorrow without going shopping.

Thanks

 

[betterman]

I think that mixing two different weights of oil gives you a weight of oil between the two that you mixed. For example mixing 10-30W and 10-40W would give you oil thats about the equivalent to 10-35W.

 

[shosleeper]

because of the chemical "strands" that make viscosity range possible in a oil, it is not a good Idea to mix in large quantities of each. the results of a mixture are not always straight forward. You may end up with a 5w-250 or 40w-45. I had a website that explained this but lost the site when I reimaged my computer. Of course small amounts of oil left behind at a change should have no adverse effects. I don't know if any of this is true(I don't always belive what I read), but I remember it came from what seemed a reputable source.