Dex III

[dnewton3]

Originally Posted By: Zero
... I usually drain the AMSOIL at 50,000mi regardless of the application and claims. How long would you recommend me using the Dex III before I drain and refill with DEX VI?



Here's a thought ...

Get a used oil analysis. Actually, get a few of them as you progress in your OCI. This is just as applicable to transmission fluid as it is engine oil.

I fail to understand the reasoning behind such questions, which rely upon rhetoric and supposition, as opposed to getting real data and using it for decisions.

You should not be asking us when to OCI your Amsoil lube. Rather, you should be telling us, as you used oil analysis along the way, when you expect to find a practical limit to the use of the lube.

Make sense?

 

[Zero]

Originally Posted By: dnewton3
Originally Posted By: Zero
... I usually drain the AMSOIL at 50,000mi regardless of the application and claims. How long would you recommend me using the Dex III before I drain and refill with DEX VI?



Here's a thought ...

Get a used oil analysis. Actually, get a few of them as you progress in your OCI. This is just as applicable to transmission fluid as it is engine oil.

I fail to understand the reasoning behind such questions, which rely upon rhetoric and supposition, as opposed to getting real data and using it for decisions.

You should not be asking us when to OCI your Amsoil lube. Rather, you should be telling us, as you used oil analysis along the way, when you expect to find a practical limit to the use of the lube.

Make sense?


Yes it does.

 

[Jeff_in_VABch]

Originally Posted By: martinq
Originally Posted By: Gokhan
Dexron-VI does have a smaller starting (new-oil) viscosity than Dexron-III. Therefore, initially, (at high temperatures) Dexron-VI will definitely be thinner than Dexron-III.

True, but the Dex3 has a fast shear-down so it won't take long for the viscosities to cross over. The operational viscosity of Dex6 is higher over most of the fluid life therefor it's more accurate to think of it as a 'thicker' fluid.

You can think of Dex3 as a 4.x or 5.x cSt fluid where Dex6 is a 6.x.


The high end synthetic Dex III fluids likely never shear down past 6.5. Every fluid is different.

Racing ATFs are generally a 4.5 fluid. It makes the shifts much firmer and the friction materials last longer.

 

[MolaKule]

Quote:
Racing ATFs are generally a 4.5 fluid. It makes the shifts much firmer and the friction materials last longer.


Most Racing ATF's use a Type F PI package and viscosities may range from 4.5 to 10 cSt.

The lower viscosity racing ATF's are used primarily to lower parasitic drag within the transmission.

 

[Gokhan]

Originally Posted By: MolaKule
Quote:
Racing ATFs are generally a 4.5 fluid. It makes the shifts much firmer and the friction materials last longer.


Most Racing ATF's use a Type F PI package and viscosities may range from 4.5 to 10 cSt.

The lower viscosity racing ATF's are used primarily to lower parasitic drag within the transmission.

From what I've read, the hardness and softness of the way the transmission shifts is determined by the amount friction modifiers (by which the surface friction is primarily determined), not the fluid viscosity (by which the hydrodynamic friction, such as in the torque converter, is determined).

References:

The history of ATF, 1939 - 2006 -- a great read on how and why different types of ATF have evolved
Afton Chemical specification handbook -- see pages 240 - 255 for Dexron-III, Dexron-IIIH, and Dexron-VI specs

 

[Whitewolf]

Originally Posted By: Gokhan
Originally Posted By: martinq
Originally Posted By: Gokhan
Dexron-VI does have a smaller starting (new-oil) viscosity than Dexron-III. Therefore, initially, (at high temperatures) Dexron-VI will definitely be thinner than Dexron-III.

True, but the Dex3 has a fast shear-down so it won't take long for the viscosities to cross over. The operational viscosity of Dex6 is higher over most of the fluid life therefor it's more accurate to think of it as a 'thicker' fluid.

You can think of Dex3 as a 4.x or 5.x cSt fluid where Dex6 is a 6.x.

No, the minimum allowable sheared viscosity for Dexron-III is 5.5 cSt, not 4.x cSt. It's the same (5.5 cSt) for Dexron-VI. In addition, minimum allowable doesn't mean that it will shear all the way down to 5.5 cSt. If it's made using quality viscosity-index improvers -- viscosity-index improvers simply being the very only reason why an oil shears -- it may hardly shear at all and the viscosity may stay close to 7.0 cSt. In most likelihood, a quality Dexron-III will be thicker than Dexron-VI in most conditions, even when it ages. This is the reason why GM doesn't recommend Dexron-VI for manual transmissions and power-steering systems that previously specified Dexron-III.

In my opinion though, you won't see any harm in manual transmissions and power-steering systems from Dexron-VI being a little thinner than Dexron-III. The viscosity difference is not that great and most protection in metal-to-metal contact (boundary-lubrication regime) comes from antiwear additives anyway.


Firstly a typical DEXRON-III fluid would shear like crazy in the first 4 to 5 k miles dropping to about 4.1to4.2 cSt at 100C by 80K. The method of getting past the testing was to rely on the 'thickening' effect due to oxidation which meant that EOT requirements were met. With DEXRON-VI however that loophole was plugged firstly by making it difficult to formulate a fluid without using at least Group III base stocks but then also making EOT requirements more stringent. In addition regarding concerns about oil film thickness, in fact the oil film thickness of a DEXRON-VI fluid is about 20% greater than DEXRON-III was, counter intuitive I know but true and supported by independent test data. A typical DEXRON-VI fluid can do at least 150K (after first change to get rid of build debris) and some have gone far mor than that without any ill effect. The most that I have seen DEXRON-III drop to is about 5.3 cSt even after 200K miles. That is one of the reasons why DEXRON-VI was invented in the first place.
Regarding the use in MT and PSF applications the reason is quite simple, those are typically bought in units that were never validated using DEXRON-III and since validation costs are VERY high it is simply not an economically viable proposition until hardware changes permit.
Hope that helps.

 

[Whitewolf]

I should have said that the most that I have seen DEXRON-VI drop to is about 5.3 cSt kv 100C. Apologies.

 

[Gokhan]

It's also possible that manual transmissions and power-steering vane pumps don't shear the ATF as much as torque converters in automatic transmissions do, and used Dexron-III will be significantly thicker in these systems than used Dexron-VI.

 

[Gokhan]

However, as I posted earlier, primary reason for GM not recommending Dexron-VI in manual transmissions and power-steering systems is probably lack of testing by them.

In my opinion, it's safe to use Dexron-VI in any system that recommended a previous version of Dexron (all the way back to the original Dexron).

In fact, conversely, you can probably also safely use Dexron-IIIH in a system that recommends Dexron-VI, but I wouldn't do so, given the improved performance specs of Dexron-VI over Dexron-IIIH and its better longevity thanks to its use of synthetic base stocks.

 

[Klutch9]

Originally Posted By: eljefino
You can go by the RPO code in the trunk and by the pan shape which is generally at least somewhat unique.

A 4T60E and 4T65E might have the same pan though.


They do indeed.

 

[jake88]

What I have been told from a major additive supplier: The new low-viscosity fluids are not good for the older 4 speed autos. The rumor was that at least one OE saw field issues.

Now, I am not so sure that I believe that rumor after following the thread and re-reading the specs. That being said, there are synthetic Dex III fluids available, and a higher viscosity multi-vehicle fluid would probably be fine (e.g. A Merc V/ATF+4 fluid)

 

[MolaKule]

Quote:
What I have been told from a major additive supplier: The new low-viscosity fluids are not good for the older 4 speed autos. The rumor was that at least one OE saw field issues.


Which additive supplier?

Did the additive supplier communicate that rumor to you?

 

[Whitewolf]

But for the wrong reasons as I tried to explain.

 

[Jeff_in_VABch]

Originally Posted By: MolaKule
Quote:
Racing ATFs are generally a 4.5 fluid. It makes the shifts much firmer and the friction materials last longer.


Most Racing ATF's use a Type F PI package and viscosities may range from 4.5 to 10 cSt.

The lower viscosity racing ATF's are used primarily to lower parasitic drag within the transmission.


Lower viscosity is definately not to reduce the drag in a racing auto transmission, but I guess that might be a benefit if it does actually reduce drag. The thinner the fluid, the higher and more consistently the converter flashes as well as better clutch plate lockup. When you run a high HP car with the trans cold, the slippage is so great that one pass can fry the transmission. When the trans is hot, you can still hear the slippage on the shifts, but it's not nearly as bad and the trans live a lot longer than you would think.

In any street car, the auto trans always feels smooth and the shifts are smooth. In a high performance car, you feel every shift. When the car is cold shifts are like bumps. As the trans heats up they go from bumps to hard bangs.

 

[MolaKule]

Quote:
Lower viscosity is definately not to reduce the drag in a racing auto transmission, but I guess that might be a benefit if it does actually reduce drag. The thinner the fluid, the higher and more consistently the converter flashes as well as better clutch plate lockup. When you run a high HP car with the trans cold, the slippage is so great that one pass can fry the transmission.


I don't know of any racer who races with cold fluids so I don't see your point.

From a thermodynamics point of view, the higher the viscosity of an oil, the more horsepower you have to use to pump that oil.

The temperature of an oil will rise because the energy from moving that oil has to go somewhere, so it goes into the heating of the oil. This is a case of energy conversion from one form of energy to another. In this case, conversion of mechanical energy to thermal energy.

Measurable and supported by physics.

 

[MolaKule]

Quote:
On another note, what make and model pump are some of you using to swap out transmission fluid without a filter change....is it a MityVac or what?


I use any fluid pump that will do the job. The problem at times is getting the right tubing that will get as far down into the transmission sump as possible without hanging up in the bends.