Originally Posted By: 440Magnum
DexronIII / Mercon V were an acceptable pairing. IIRC the MercV spec included everything about DexIII spec plus a couple of other requirements. Don't think it works that way for DexVI. And has been pointed out many times, the Dex III spec is so old that its very possible to meet its intent while violating it in a literal sense. The spec was written anticipating a lot of shear-down that modern fluids don't exhibit, so a modern fluid can easily start out thinner than what the spec calls for and still be as thick in service as the real engineering need behind Dex III.
So I'd say its a case-by-case basis. I wouldn't use anything but ATF+4 in a vehicle that calls for it, but in a vehicle that calls for Dex III there are a lot of options that meet and exceed (without detrimental effects) the Dex III spec.
I have mentioned on other threads that the dynamic friction coefficient is one of the important characteristics in an ATF.
When it comes to most Dexron and Dexron-type LV fluids, the friction coefficients in the various transmissions are very close.
As 901 mentioned, the exception is Chrysler ATF+4 which is considered a "highly modified" ATF, so the Multi-vehicle fluid MAY or may NOT offer shift performance comparable to the ATF+4.
The research that the additive companies executed to develop Multi-vehicle fluids was very extensive.
I am not trying to convince to use a Multi-vehicle ATF.
If you are not comfortable with Multi-vehicle ATF's then you DO have choices, but I can tell you that many of the OEM branded fluids, such as NissanMatic J, S, is not as robust a some of the aftermarket fluids.