dex 3 to dex 6 on 14k Buick

[zeng]

Originally Posted By: 69GTX
Ford's Mercon V is essentially a semi-synthetic DEX III with a stronger add pack. It's been around since about 2000. My 2002 Lincoln trans calls for Merc V. No way I put the Valvoline ATF-LV in there. While regular conventional Dex 3 probably shears down by 40% during the recommended OCI, the Merc V only shears down by approx 19% which still keeps it above the Valv Max Life visc of 5.8 even after 30K miles. The MaxLife supposedly shears down by 3% or less. Synthetic ATF Dex 3's like Mobil 1 ATF start out around 7.5 cSt and stay above 6.8 for an OCI (approx 3-10% shear rate). Plenty of options without resorting to a 5.8 cSt starting viscosity for a transmission that specced 7.0-7.5 to begin with.

+1
Like to pick your brain on typical residual KV@100*C at 25-30K miles OCI of :
a)Mobil ATF 3309 (virgin 7.2 cSt);
b)OEM Mitsubishi SP III (virgin 7.4 cSt), and
c)OEM Toyota Type T IV (7.3?).
My rule of thumb has been 5.8- 6.2 cSt KV@100*C.

 

[69GTX]

Shear rates for some ATF's

Someone posted the above article here which is what I'm using to compare shear rates. As long as you know if it's conventional, blend/semi-syn, or full syn you should be able to get in the ball park.

 

[MolaKule]

Originally Posted By: zeng
Originally Posted By: SoNic67
So you gonna switch from an ATF with viscosity at hot of 7.2-7.4 cSt to one that has 5.4-6 cSt, just because some people told you that "it's better"?
The Dex VI is formulated for newer design Low Viscosity transmissions (fuel economy). Dropping it into older design transmissions designed for Dex III is wrong (will create a lower working pressure with existing pump).
I would use either Castrol Merc/Dex (7.2 cSt) with LubeGard Red, or Castrol High Mileage (8 cSt). Or, if you are into Mobil 1 use their Synth ATF, it has 7.4 cST. Don't even look at other "synthetics", they are almost all LV.

+1
At 30k drain/fill, it probably provides higher operating viscosity(and hence components protection) against a Dex VI.


Retained viscosity at longer mileage is what provides film strength.

It is the AW components in the additive package that provides the primary AW protection.

Changing FF at approx. 10k miles and every 35k or so thereafter is good insurance.

 

[LeakySeals]

If you want "better", use M1 ATF. Its a syn thats thick enough for a dex III tranny. DO NOT use maxlife. Too thin. Oreilly brand Dex III-h is readily available on the shelf and works great... That is if you have an O'reillys near you.

 

[901Memphis]

Originally Posted By: Fsharp
If you're choosing between Supertech dex 6 or III then I'd get the 6, but if you're willing to pay for a regular viscosity synthetic that is Dex III compatible you might as well get one of those and not have to worry about too low of viscosity.


Maxlife is not too thin. I'm using it in my new 4t65e right now along with many others, it shifts perfectly

 

[HangFire]

Originally Posted By: SoNic67
"Shear down quickly" it's a myth.

Originally Posted By: 69GTX
Shear rates for some ATF's

 

[Fsharp]

Originally Posted By: 901Memphis
Originally Posted By: Fsharp
If you're choosing between Supertech dex 6 or III then I'd get the 6, but if you're willing to pay for a regular viscosity synthetic that is Dex III compatible you might as well get one of those and not have to worry about too low of viscosity.


Maxlife is not too thin. I'm using it in my new 4t65e right now along with many others, it shifts perfectly

I'm sure it works well. If he's going to buy more expensive fluid though, he might as well get some that's not low viscosity. Like RP Max ATF, Redline D4, Amsoil multi-vehicle, Mobil one synthetic, etc

 

[901Memphis]

Originally Posted By: Fsharp
Originally Posted By: 901Memphis
Originally Posted By: Fsharp
If you're choosing between Supertech dex 6 or III then I'd get the 6, but if you're willing to pay for a regular viscosity synthetic that is Dex III compatible you might as well get one of those and not have to worry about too low of viscosity.


Maxlife is not too thin. I'm using it in my new 4t65e right now along with many others, it shifts perfectly

I'm sure it works well. If he's going to buy more expensive fluid though, he might as well get some that's not low viscosity. Like RP Max ATF, Redline D4, Amsoil multi-vehicle, Mobil one synthetic, etc


Maxlife is a top quality synthetic and I get a gallon for $17