A quick update on my recommendation for the Tremec manual transmissions before I go offline for a few months. Won't check this thread again for several months, so I apologize in advance if you have any questions.
I recommend (for Tremec manuals):
AMSOIL Torque-Drive Synthetic Transmission Fluid (product code ATD1G, commonly referred to as AMSOIL ATD)
Background:
The issue has been that AMSOIL has two automatic transmission fluids that are labeled to be suitable for Dexron III applications by AMSOIL, the AMSOIL ATF and the AMSOIL Torque Drive (ATD).
I have been using the AMSOIL ATF, a Dexron III fluid, in my 02 Z06 and 06 CTS-V for years with good results. Last year, AMSOIL reformulated this fluid and slightly lowered its hot cSt viscosity from about 7.2 to 6.8 so as to make it suitable for GM's new Dexron VI specification. A nominal Dexron III fluid has a new hot viscosity of about 7.3, but shears rapidly down to about 5.0-5.5. After 10k miles, my factory fill Dexron III in my CTS-V had sheared down to 5.0. I replaced it with AMSOIL ATF and ran it for 6k miles until I just swapped it out with the AMSOIL Torque Drive ATD. After 6k miles, the AMSOIL ATF's viscosity remained at 6.8 showing extremely good shear stability. I'll post the actual Blackstone Lab results when I return.
Given that Dexron III starts with a higher viscosity than the AMSOIL ATF, but the AMSOIL Torque Drive ATD hot viscosity of 7.4 essentially matches that of new Dexron III, I queried AMSOIL about why they recommended the ATF over the ATD for Dexron III applications. After analysis of the issue, AMSOIL revised their primary recommendation for Tremec manuals requiring Dexron III from the AMSOIL ATF to the AMSOIL Torque Drive ATD. The
AMSOIL Online Product Application Guide now shows the ATD as the primary recommendation and the ATF as secondary. I agree with this based on the ATDs higher viscosity and the fact that it has no viscosity modifiers and thus is extremely shear stable. I feel these make it the better of two good choices for the Tremec manual tranny.
Both the AMSOIL ATF and AMSOIL Torque Drive ATD use a synthetic Group IV, PAO basestock fluid and are very similar to each other. The primary difference is that the ATD has a little higher viscosity (7.4 vs 6.8) and no viscosity modifiers. However, the ATF is an extremely shear stable fluid as borne out by my 6k miles of use with no viscosity loss. For those with the ATF in their trannies, I would not run and change it out. For future changes, I'd use the ATD. I will change the tranny fluid in my Z06 (which I raced with this past October), from the ATF to the ATD for my races this upcoming spring.
FYI, I changed my CTS-V to the ATD a few weeks ago and have been driving with it in cold winter weather. I noted no difference in shift feel with the new fluid.
Note: For automatics, I still recommend the
AMSOIL ATF (product code ATFQT)
