Mixing transmission Fluid?

[Wardog]

I just did a 48RE service (pan fluid and filter only. . no flush) and bought some valvoline ATF-4 fluid. Problem is, I had two quarts of Mopar ATF-4 on hand, so I only bought 6 quarts of the Valvoline. I didn't realize the Valvoline was synthetic until I began opening it. So. . my question is, can I top off with the Mopar or is it not good to mix it with synthetic? I'd be adding a quart and a half or so. It's no problem to pick up some more Valvoline ($2 cheaper p/qt than the Mopar), I'd just hate seeing the stuff on my shelf go to waste.

 

[WNowlan]

The Mopar fluid is also a synthetic. You will have no problems mixing these two fluids.



Compatability with non synthetic and synthetic is not a problem with the modern fluids we use today. You do lose the benefits of having a full synthetic when you mix.



In your case they are both made with Group III base oil.

 

[Wardog]

The Mopar fluid is also a synthetic. You will have no problems mixing these two fluids.



Compatability with non synthetic and synthetic is not a problem with the modern fluids we use today. You do lose the benefits of having a full synthetic when you mix.



In your case they are both made with Group III base oil.

If they're both synthetic, how do I lose the benefit of having full synthetic when I mix them?