Borg Warner T45 ATF viscosity

[buck91]

So I'm over thinking. Should keep it simple, pick up a couple quarts of MC Mercon V at my distributor... but that's not oru way is it?

Finishing up some work on my 1996 Mustang GT with the Borg Warner T45 5 speed trans which is spec'd for Mercon. Ford now back spec'd Mercon V for all Mercon applications. I have run Mercon V in this transmission with fine results. I have a jug of Maxlife ATF on the shelf, and nothing else. Jug says Mercon LV on the back. I know valvoline's stance that maxlife is more shear stable and ends up operating at roughly the same viscosity as dex/merc.

Does anybody know if this T45 would be better suited by using a quality mercon/mercon V fluid like the Motorcraft or Mobil 1? I would expect both those fluids to be top notch and rather shear stable, with a higher starting viscosity. No transmission issues I am trying to cover. Car will be driven during late spring through mid fall only but will be driver with great spirit. Most seals are new. Always been a quiet and fair shifting trans. Not worried about service life of fluid but want to provide a good level of protection and also has the smoothest shifts reasonably possible. Thinking the thinner maxlife might increase notchiness? Never experimented before, what do you guys think?

 

[69GTX]

The thinner Max Life (5.8-6.0 cSt) will probably be less notchy since it's thinner, especially when cold and warming up. But, it's also starting well below the viscosity of the Merc V and M1 ATF (7.2-7.6). While the Max Life is very shear stable and has a great add package (probably much stronger than a typical Mercon V), I'd prefer the Mobil 1 ATF which apparently meets Merc V and Dex 3 specs and is fairly shear stable as well. GM has noted they don't feel the Dex VI fluids are suitable for their manual (Tremec) transmissions. And to me Max Life is a Dex VI/LV fluid.

The Mercon V would probably be less notchy than the Mobil 1. No real downside to using that other than maybe having to change it out sooner than a Mobil 1 if it's not as shear stable. And I wouldn't expect the add pack of the Merc V to be all that stout...though I can't say I've seen a VOA or UOA on one of them.

 

[JasonC]

I have always used and loved Royal Purple Synchromax Synthetic MTF in Mustang V8 manual trans.