dexronIII vs dexronVi

[pjc360]

I am told that i need to run dexronIII in my transmission by the owner of the transmission shop that re-built my transmission. transmission is a A-518 non lock up transmission in a 1991 dodge power ram 150. I have been doing some reading on the newer dexronVi and it says it is backwards compatible to dexronIII and will work in anything calling fro dexronIII, dexronII was factory fill in my transmission back in 1991, what i have learned is dexronIII was devolped and released by gm in 1993, dexronVi was made in 2005. Some people say that dexronVi is a full synthetic and some say that it is not a synthetic so wich is it? my next question what fluid should i use? i have permanatly decided on a dexron fluid, now im just trying to decide between dexronIII and dexronVi. would a person feel firmer shifts with dexronIII or the dexronVi? obviously the dexronVi will last longer and protect better against heat.
Although the dexronIII is cheaper and im guessing will provide firmer shifts over the Vi, so wich one do i go with?

 

[mechanicx]

DexVI is either a synthetic blend or full synthetic. It is more sheer stable than DexIII so the viscosity difference is close in reality. DexVI is the better fluid. Some people don't believe DexVI is really backwards compatible but I dont see any reason to think it isn't.

 

[chubbs1]

I would go with the DexVI no question. It is fully back compatible and of a much better shear resistant basestock with a more up to date additive pack. I am NOT a transmission re-builder though, so I would personally talk with the shop owner and ask why he believes that DEX-III needs to be used. Maybe he has a persuasive argument for it. The facts I know are the DEXVI is higher quality and compatible according to GM.

 

[SteveSRT8]

Many older cars with high mileage have issues with DexVI. But it is truly a superior fluid.

It should work very well in any healthy trans.

 

[artbuc]

Originally Posted By: SteveSRT8
Many older cars with high mileage have issues with DexVI. But it is truly a superior fluid.

It should work very well in any healthy trans.


Please say more. Would you consider a 99 Toyota Avalon with 110k miles old/high mileage? What kind of problems should I expect since I recently replaced D3 with D6? Thanks.

 

[SteveSRT8]

It's only in a particular few. I've heard things like slippage and harsh shifts/engagement.

All of our fleet trucks love it, and it's lifespan is leagues better than DexIII.

YMMV

 

[Whitewolf]

You are correct in that it is much better than DEXRON-III.

To give you all some background when the change from TASA to DEXRON-II took place many problems were attributed to the 'new' fluid. The fact was that the earlier fluid left so much 'gunk' and dirt behind that was undetected until the 'new' fluid arrived!

The DEXRON-II fluid had a higher level of dispersant quality than the previous fluid and therefore the new fluid was not the problem it was really the old one!

That could be what some people might observe if they are moving to DEXRON-VI from some older and perhaps even unlicenced 'dexron' ATFs that they used before?

 

[pjc360]

well my transmission is not a high mileage transmission, it dont even have 1000 miles on it since being re-built. i asked the guy who re-built my transmission about using dexronVi and he said oh no dont use dexronVi thats a synthetic, like synthetics were a bad thing? he said just use plain old dexronIII you dont wanna use a synthetic. then i have talked to some people who say its not a synthetic. wich one would give firmer shifts? the dexronIII, and why would a synthetic transmission fluid be a bad idea? he didnt really explain he just said stay away from synthetics....

 

[mechanicx]

DexVI should give similar shifting to DexIII. Which is what you want and why it is backwards compatible. As I mentioned Dex VI can be a blend or full synthetic. Some mechanics erroneously believe "synthetic" fluids whether motor oil or ATF can cause problems in equipment that was not originally speced for synthetic. That's not true.

 

[RF Overlord]

Unfortunately many otherwise highly competent technicians are woefully behind in lubrication knowledge. I certain don't claim to be an expert in either oil or transmissions, but I cannot see how using a synthetic ATF could be bad in any way other than *perhaps* being an unnecessary expense in some cases.

Here's another thought...since GM no longer licenses D-III, is it better to use an unlicensed, and possibly inconsistent, product or to use the current version (D-VI)?

 

[pjc360]

I just wanna use whatever is going to serve my transmission best, I never knew there was a newer dexronIII devolpment called dexronIII h, from what i read its spos to be a little better fluid then the regular dexronIII. I was also informed that all the currently made dexron/merconIII was made to the dexronIII h spec, is this correct? the dexronVi is no doubht a far superior fluid to the dexronIII and i do not understand why the guy who re-built my transmission says to stay away from synthetic atf's ether? i'm guessing he thinks synthetic atf's are too slippery for the old hydraulically ran transmission. I was wanting to use the Valvoline MaxLife ATF untill i ran that by my builder and he said not too??? i also asked about using dexronVi and he shot that down too?? so what dexron fluid would suit my transmission best, the dexron/merconIII h fluid the valvoline maxlife atf or the newer dexronVi fluid? again the transmission is a non lock up chrysler A-518 transmission in a 4x4 truck that will see some high temps quite often from driving up mountains and using it to haul a few things here and there.