Dex-VI vs Dex-III..Nice Read; Facts on both fluids

[Steve S]

Originally Posted By: onion
Well, the difference in friction properties that you describe with Dex VI compared with Dex III are directly opposite of what I've observed in my 4T65E. It shifts MUCH better with Transynd. And it shifted much better with a few years ago with Supertech DexIII (before I flushed with Dex VI).

With Dex VI, the full-throttle 1-2 shift slips & grabs... aka 'rooster-tail'. And I'm not the only one who has experienced this when running DexVI in an older transmission designed for Dex III.
Could the difference be the viscosity?

 

[Whitewolf]

Simple answer is no.

 

[Ramblin Fever]

Nice article....but all I'm going to say, is that I attempted Dex VI in my older GM transmission and found shifting to be harsher.

Switched back to my trusted Dex III, Castrol Import to be precise, and all is smooth again. Currently have 200k on original transmission, why mess with a good thing....if it ain't broke, don't fix it.

Not going to switch to Dex VI in my wildest dreams with this transmission.

 

[mechtech2]

The DexVI in that article's chart seems to grab better , and not change over time as much as the old stuff.
This indicates to me harsher shifts [not necessarily bad].

I wonder if it is enough for manual tranny's that spec ATF?

 

[Ramblin Fever]

I don't know...all I can say is when I tried Dex VI the shifts were quite a bit harsher.

My truck never shifted that harsh even when new 15yrs ago....my opinion is why fix something that isn't broke???

I do partial drain/refills on this tranny every 15k miles depending how much mountain driving, or towing we do; fluid always comes out good/clean for over 200k miles now.

I don't believe the Dex III is masking problems either; if a transmission is failing NO fluid's going to stop it.

 

[NightRiderQ45]

Last weekend, I did a drain & fill with two qts of ST Dex-VI, one qt of Nissan Matic-D and one qt of Coastal Dex-III (licensed)...in 200mi so far, no shifting problems like expected. Instead of changing out every 15k, I'm going to bump it up to 30k now.

 

[wtd]

I wonder how Dextron VI would do in the tranny of my 1992 Cavalier that specs Dextron IIE. Car has 146,000 miles on it and I've done a couple of fluid and filter changes with Dextron III spec fluid in the four years I've owned it. It has always had a shudder problem which is worse in the colder weather. I may try it on the next change.

I used Valvoline Dextron VI in my 2004 Monte Carlo SS with the Supercharged 3800 and the HD version of 4T65 in it and it seemed to help the shifting.

I'm afraid to try it in my 98 chevy truck with the 4L60E because when I used Mobil 1 synthetic tranny fluid in it, the tranny felt like it was slipping. I changed back to conventional Dextron III and it went back to normal.

Wayne