I'm due for a ATF fluid change on my '95 Saturn SC1 with 221K miles. I have about 1 3/4 quarts of Mobil 1 left over from my previous change. Would it be prudent to mix this with something like Maxlife ATF? If it matters, this is Dex III.
Yep, it will be fine.
I have 3-4 different types of Mercon V in my F-150 right now.
Fresh and meets the specs is all that really matters of a fluid.
And a quart of two of one type isn't going to change all that much in a system that holds 12 quarts.
Mix Dex III with MaxLife, did that exactly in my Tacoma specing DexIII with a drain and fill. Been a few years and have done another since and well over 20k miles now and all is well. ML is compatible with Dex III. As are a good number of other multi vehicle ATF's.
I have mixed and matched and haven't experienced an issue with my Cherokee (Toyota transmission).
It specifies DexIII/Mercon.
When I bought it, I did a drain and fill with Mercon V fluid. Have done a few drin/fills with leftover Mercon V then, when I ran out of that I used Supertech DexIII fluid. Last trans fluid change was with Mobil ATF D/M.