Originally Posted By: edhackett
Here's your proof of at least one possible problem. It appears to be especially critical when using group III oils, as both of these are.
Mix of oils destroying cold flow properties:
http://www.infineum.com/Documents/Crankc...icants-2010.pdf
Ed
I wanted to read that article and it's a bad link!
Also from Valvoline's website:
» Can we mix two different brands of engine oils?
Technically it is possible to do so provided the new oil has the same performance level as the old oil. However, mixing oil brands (read topping-up) on a continuous basis is not a good idea. You should also be aware that engines typically go through a period of adjustment when making the transition from one oil to another. Because brands could be formulated with different additive chemistries, a new brand may act differently than the old one at first. Increased oil consumption and leaking seals are common adjustment problems.
Companies get their additive packages from a small amount of places and the possibility of issues isn't large, but it is there. I would not mix something like Red Line or Amsoil with off the shelf synthetics, but I would mix off the shelf synthetics with each other without worrying. My car very rarely encounters two oil changes in a row of the same brand of oil and I have no leaks or oil consumption FWIW.
In short, I agree with dparm that you wont have any issues mixing those oils.