Originally Posted By: TheBus36
I'm not mixing viscosities. Just mixing major brands that are supposed to have the same requirements as stated in the owners manual. In my Tacoma, I have mixed 5W and 10W 30 conventional but both both viscosities are acceptable as per the owners manual.
You're not mixing viscosities, though you are mixing different additive packages. I'd at least try to keep them in the same family.
That means mix away the Pennzoil, Quaker State, Castrol. But keep those separate from the Valvoline/Napa and also the Mobil 1's. Those are 3 very different add packs. I'd try to keep them in the same family....ie high calcium, magnesium, or sodium. No, your engine won't blow up if they're mixed.