Dex VI and Dex III ; Viscosity -vs- wear?

[Loobed]

I started using Dexron VI a few years ago (in my 2001), and I am now rethinking whether or not Dexron VI is better than Dexron III. I read that one of the reasons GM came out with Dexron VI (with a lower viscosity) was so that there was less resistance in the transmission so vehicles could get better fuel mileage. The viscosity is only slightly less than older Dexron III. Does the slightly lower amount of viscosity increase wear any amount?

I would rather get 0.2% less mileage than 0.2% more wear. Both amounts seem insignificant, but I would rather pay a little more for fuel now, than have to spend the money to repair the transmission. Even if I buy 1 extra year of life out of my tranny (out of ~25 years), it is worth it to me.

 

[oggb]

Under normal circumstances it won't make a difference. Manual transmissions that ran synchromesh didn't appear to fail any more often than transmissions running 80w-90.

If you're drag racing or towing heavy it could make a difference. Everyday driving? Wouldn't even sweat it.

 

[LargeCarManX2]

The new Dex is superior to the old Dex, GM needed a better fluid for the new generation transaxles.

 

[Loobed]

Originally Posted By: LargeCarManX2
The new Dex is superior to the old Dex, GM needed a better fluid for the new generation transaxles.


for wear?

 

[Towncivilian]

Doesn't Dex VI start out at a similar viscosity to Dex III's viscosity after initial shearing?

 

[SteveSRT8]

The Dex VI spec is greatly biased towards long life. A much better fluid than Dex III and designed for extended intervals.

 

[LargeCarManX2]

Originally Posted By: Loobed
Originally Posted By: LargeCarManX2
The new Dex is superior to the old Dex, GM needed a better fluid for the new generation transaxles.


for wear?



Wear, longer drain intervals, equiptment life, higher transaxle temps...the list goes on!

 

[Samilcar]

Originally Posted By: Towncivilian
Doesn't Dex VI start out at a similar viscosity to Dex III's viscosity after initial shearing?


This was my impression as well. Dexron III, being a non-synthetic conventional fluid quickly shears down from its initial starting viscosity. Dex VI, being synthetic, starts out at the same lower viscosity to which Dex III shears, but maintains its viscosity.

 

[Ken2]

Keep in mind that Dex-VI is a much tougher spec than Dex-III. One example is that no conventional base oil could meet the Dex-VI performance requirements. It took a syn blend or better to meet the performance requirements.

 

[WishIhadatruck]

Dex III can definitely shear down, Dex VI is suppose to be better. As an example, my 2001 Grand Prix with the 4T65E trans. I bought it new and have done a pan drop and filter change every 30k miles since (174k miles now). It takes 7.5-8 qts to refill with a filter change, that is a pretty good % change with each service. At the 30k and 60k changes I filled it up with M1 ATF which met the Dex III spec. at the time. When I did the 90k change I pulled a sample. The viscosity of the fluid (mostly M1 ATF) was "cSt @ 100ºC 5.72"

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1228387

Definitely thinner than Dex VI when new. I've been running Dex VI since. When I get to 180k miles this summer I'll pull another sample and see how they compare. Wear might not be a fair comparison (I've had a few transmission quirks with no repair) but the viscosity comparisons should be interesting. I think I'll try Redline D4 next.

My wagon with the 4L60E trans. seems to love the Dex VI, I probably won't change anything with it.