Dexron VI and elastomers

[JHZR2]

I have read that Dex VI may not be an optimal replacement for all Dex III/II applications due to elastomer incompatability. Is there any truth to this, and is there a good way to determine how/if it will be a valid concern? My applications are all 30 year old MB ATs, specced originally for Dex II.

Thanks!

 

[The Critic]

Give whitewolf a call.

 

[mechanicx]

Elastomer compatibility and seal swell characteristic were suppose to be part of the parameters for backspecing Dexron VI. I guess it's a similar question to do Group III oils offer the same seal compatibility characteristics as Group I and II formulations. I don't know or think Dex VI that is a synthetic blend as opposed to full synthetic would make a difference. I have faith in Dex VI and the backspecing recommendation.

 

[Whitewolf]

I think I can help you with this. DEXRON(R)-VI was designed to be fully backward compatable with earlier transmissions including the various materials used. This is the difficult part since transmissions built way back when often used materials that really would not or should not be considered as suitable for use in a modern transmission. Some of those seal materials actually relied on the fact that Group I or even Group II fluids would cause them to swell and therefore remain viable. The other problem with those fluids though was oxidative stability which was not good by today's standards. Hence the arrival of Group IV in the automotive arena followed by an increased use of Group III due to cost issues with PAO.
The problem with Group III and Group IV is that they do not swell seals much, if at all, and therefore require more and different seal swell agents than previously used. These days those agents are normally, although not always, Esters (Group V). The use of Esters is ,in part, to allow seal swell to simulate that of earlier fluids without the downside of oxidation instability. That is one of the reasons how fluids such as DEXRON(R)-VI can be made backward compatable.
The problem with these newer fluids is that when are about to be introduced the materials engineers test them! That's when they find out that they made bad choices in terms of seal material suitability for use in newer transmissions. Now ask yourself is it better to admit that you screwed up or is it a better option to blame any problem on the new fluid? That's how the story of the newer DEXRON(R) and MERCON(R) type fluids being bad on seal performance has come about. Sorry about the rather long explanation but I thought that a bit of background might help (you might be relieved to know that I actually cut it short).
In summary if I were you I would not hesitate to use the DEXRON(R)-VI product that you refer to as long as it is a real one as outlined on the recently posted list. I would also suggest that you do a drain, fill and then do that again after a few miles, say a couple of thousand.
Regards
WW

 

[Tom NJ]

From the GM patent (for what I understand is the standard formula for Dexron VI):

"According to an embodiment of the present invention, the composition is comprised of an additive blend and a base stock. The additive blend preferably includes an additive package, a viscosity index improver, and an ester......The ester preferably consists of one or more lubricant grade esters such as a pure adipate diester base stock containing short chain branched alcohols. The ester is used as a seal swell and also as a solvent for the additive packages. An exemplary pure adipate diester base stock containing short chain branched alcohols is Hatco 2906 by Hatco Corporation (Fords, N.J.)"

Chemical Type in %

Additive Package 7.18
VI Improver  3.60
Ester 11.82
PAO, 2 cSt 9.40
PAO, 6 cSt  68.00

PAOs have a tendency to shrink and harden some types of common seal materials, and blending in some synthetic ester is essential for proper balance.

GM Patent

Tom NJ

 

[Whitewolf]

That is what the patent states. The ester is generally used to provide both seal swell and to aid solubility in PAO based formulations.

 

[nascarnation]

At Allison we were definitely worried about seal life with Dex VI. That's the primary reason that TES 389 was released as a spec to continue Dex III spec fluids in the marketplace for those who didn't want to step up costwise to full syns like TES 295.

https://fdlrd.swri.org/Allison/ApprovedFluidsList.aspx?Id=2

 

[Ken2]

I know that DEX-6 is recommended for all GM Hydramatic transmissions and certain Allisons. Where is it published that DEX-6 is suitable for every transmission that ever used any Dexron ATF?

 

[cchase]

Many MT's that specced Dex III are specifically not compatible with Dex VI. This doesn't answer your question, but it certainly adds to the notion that there is some kind of incompatibility somewhere.