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

[Whitewolf]

Originally Posted By: onion
Maybe WhiteWolf or somebody more knowledgeable than me can chime in here, but it's my understanding that ONE reason GM came out with DexVI was to address shudder problems with some of their newer transmissions... which implies to me that the friction properties of DexVI are at least somewhat different than DexIII.

And even though DexVI has been been declared backwards-compatible... it's still a fact that lots of older transmissions were not designed for this particular fluid. It may be 'close enough', but it simply isn't the same ATF as, say, DexIIIG.

So it should come as no surprise that at some older transmissions don't 'like' DexVI. The 4T65E in my '01 Lumina does NOT work well with DexVI- it made the full-throttle 1-2 shift do a sickening slip & grab thing. I kept the DexVI in there for maybe 25k miles and just avoided full-throttle 1-2 shifts, thinking that maybe the trans. was on its way out. Then just as an experiment, I did a full flush with TranSynd (which claims DexIIIG on the jug- which is what this vehicle originally required). I let the wife drive it for maybe a week before I tried to full-throttle 1-2 shift... to let the clutches soak in the new fluid. And it shifts MUCH better. The full-throttle 1-2 shift is still softer than I'd prefer, but it's perfectly normal. No more slip & grab.

The 4T60E in my '94 Corsica, on the other hand, shifted perfectly with DexVI. Over the years, I ran supertech Dex III, then Penzoil Dex VI, then Transynd in that transmission... and never felt ANY difference in shift quality regardless of what fluid was in there.

So while I don't think there's anything 'wrong' with DexVI, and I would definitely use it in a vehicle that specifies that fluid... it may not be ideal for some older transmissions that were designed for DexIII. And it'll work fine in others... possibly most of them.


First of all, DEXRON-VI was not brought out in order to address shudder problems, that had already been accomplished by the previous DEXRON-IIIG and -IIIH formulations.
The objective of DEXRON-VI was to establish a standard that was far more stringent in terms of ATF quality and durability than had been seen previously. This has been demonstrated in various studies and has been presented in a previously quoted SAE paper.

 

[wgtoys]

Although Dexron VI starts out as a lower viscosity fluid than does virgin Dexron III, the Dexron III fluid shears down fairly rapidly while Dexron VI is much more stable over time. This stability is how a fluid which starts life being thinner than the other stuff can still be fully up to the job as it maintains its viscosity. Slightly aged, but not yet worn out, Dexron III ends up being much thinner than Dex VI.

 

[unDummy]

Clutch to clutch shudder vs clutch on steel is why DexronVI was created. Love those new transmissions. DexronIIIG and IIIH were both a failure!
All other benefits were a side effect of making clutch-to-clutch work and last.

 

[Whitewolf]

Originally Posted By: unDummy
Clutch to clutch shudder vs clutch on steel is why DexronVI was created. Love those new transmissions. DexronIIIG and IIIH were both a failure!
All other benefits were a side effect of making clutch-to-clutch work and last.

 

[onion]

Originally Posted By: Whitewolf


First of all, DEXRON-VI was not brought out in order to address shudder problems, that had already been accomplished by the previous DEXRON-IIIG and -IIIH formulations.
The objective of DEXRON-VI was to establish a standard that was far more stringent in terms of ATF quality and durability than had been seen previously. This has been demonstrated in various studies and has been presented in a previously quoted SAE paper.


So in your opinion, what accounts for the difference in shift quality that I (and others) have experienced?

 

[Whitewolf]

If you take a look at the spec you will see that the friction requirements remain the same but an effect of improving the friction durability is that the more modern additive pack is less inclined to 'rooster tail'. This quality can be seen in the published SAE paper information that I have referred to previously (can't remember the number just now) but if you look at the end friction I think you will see what I mean.

 

[onion]

So in your opinion, what accounts for the difference in shift quality that I and others have experienced with Dex VI? Over-active imagination?

 

[Whitewolf]

My opionion is that what you observe in shift is what I just tried to explain. End torque was and is a report item with no actual limit.

 

[onion]

I'm really not trying to be obtuse here, but can you dumb-down your answers for those of us who don't test various ATF's for a living? Without some context, "rooster tail", "end torque", "report item", and "no actual limit" don't really tell me a whole lot.

I'd be interested to see the SAE paper, but they generally require $$ up front just to view them.

 

[unDummy]

Whats the point of a spec with no limit?
Pretty much is a pro argument in the never ending debate concerning multi-vehicle/universal ATF.

We have all these requirement with no actual limits as long as you report the item

Talk about politicking.

It would've been more honest for GM to say that DexronIIIh was just really pathetic and they finally pulled up the pants in engineering to do something about it.
Or, was it sponsored by exclusivity to Afton? Pretty much akin to the company that supports the winning politician, gets all the contracts.

 

[Whitewolf]

Sorry, we just get used to using jargon.

If you take a look at the trace from an SAE #2 friction test you will often observe a rise in friction just prior to 'lock up' in other words as the sliding speed approaches zero the friction value increases. We call that a 'rooster tail because that's what the trace looks like (to a greater or lesser extent). That is what results in a harsh shift
End torque is just another way of looking at the same thing.
Report item means that when test data is submitted those values have to be presented to the approving authority even though there is no published limit. Most OEMs do however reserve the right to require additional testing if they are not happy with the appearance of even the report items.

Now, have I made it better or worse? If it is the latter pm me and I will try harder!

 

[onion]

Yes, that helps me understand what you're talking about.

Now if I understand correctly, this means that with Dex VI, the difference between dynamic vs. static friction will generally be less than what you'd see in Dex III. Does this not imply that the frictional properties are somewhat different?

Now correct me if I'm wrong here, but the grab & slip shifting that my 4T65E transmission experienced with DexVI seems inconsistent with what you're telling me. It implies MORE 'rooster-tail' than a fluid that doesn't cause the slip & grab behavior. Right?

I've no doubt that ON PAPER, Dex VI is a huge improvement over Dex III. And I've no doubt that ON PAPER it outperforms many 'premium' ATF's that are popular on this site. But the fact is that I and others have experienced less than desirable shifting characteristics when using Dex VI in an older transmission that originally specified DexIIIG or the like. And I'm trying to wrap my little mind around why.

 

[Whitewolf]

The effect should be less and smoother unless there is another problem.

For what it's worth that is not just on paper but also demonstrated by extensive dyno and vehicle testing.

 

[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.

 

[daves87rs]

So...from what I'm reading, My 04 Cavalier 4 speed should be fine on dex VI if it is in good shape( which it is). The 4speed autos in the J bodies seems to hold up well over time (the 3 speed autos, almost as much).

So a switch to something like Valvoline dex VI (full syn) should improve my shifts?

 

[daves87rs]

Originally Posted By: Whitewolf
The effect should be less and smoother unless there is another problem.

For what it's worth that is not just on paper but also demonstrated by extensive dyno and vehicle testing.



With testing (or abusing) of trans to see what they can stand, I would think...

 

[Whitewolf]

Some of that yes but also to test fluids A to B is more difficult.

 

[SteveSRT8]

there is the additional problem of never knowing the condition of the trans we are anecdotally referring to here.

Bad pumps, worn clutches and shot TC's are never fixed by a change of fluid!

 

[Whitewolf]

What are you talking about? I might be missing something?

 

[G-MAN]

Originally Posted By: Whitewolf
What are you talking about? I might be missing something?


I think what he's talking about is a high-tech fluid like Dex VI can reveal problems with a transmission that were being masked by (old) Dex III fluid.