Originally Posted By: dparm
In a pinch, it's fine. I wouldn't make it a habit of running weird oil cocktails for a car's entire life.
Once in a while for an oil change, just to make use of some orphan quarts, it should be okay.
I'm with you, though, in that I would not make a regular practice of it, unless the vehicle in question has reached beater status.
Even then, with a little planning, you can usually use matching quarts for an oil change.