Viscosity index improvers in ATF pros and cons?

[porcupine73]

Anyone have any thoughts about viscosity index improvers in automatic transmission fluid? I noticed that Amsoil's Torque-Drive says it does not contain VI improvers, which Amsoil says means 'no VI improver shear down regardless of operating the environment.'

I noticed the Amsoil Torque-Drive has higher viscosity at low temps (i.e. 8411 cP @ -40 deg. C) than other fluids (i.e. 5190 cP @ -40 deg. C for Mobil 1 Synthetic ATF).

Would an ATF that is relatively thick when cold cause any problems?

Has anyone tried Amsoil Torque-Drive in a passenger vehicle? What brands of synthetic ATF (for Dexron III applications) do folks suggest?

Thanks!

-Louis

 

[Burbanite]

I'm using Redline D4-ATF in my 4L80E transmission which is in an 02 2500 Suburban. I noticed since the change it shifts a little better and runs cooler than with the petroleum ATF. You might want to check this stuff out as another option.

 

[MolaKule]

quote:

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Anyone have any thoughts about viscosity index improvers in automatic transmission fluid? I noticed that Amsoil's Torque-Drive says it does not contain VI improvers, which Amsoil says means 'no VI improver shear down regardless of operating the environment.'


Would an ATF that is relatively thick when cold cause any problems?

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VII's in mineral oils is a necessity, but not in synthetic fluids, since full synthetic fluids have the Viscosity Index to span the temperature range without becoming too thick or too thin.

Certain VI's in the past have had problems with shearing but modern polymer chemistry has pretty much solved that problem.

At -40 C or -40 F it's going to take some time for ANY fluid to warm up so don't worry about it.

 

[porcupine73]

Burbanite, thanks for the suggestion. I'll have a look at the specs. I currently run Mobil 1 Syn ATF.

Mola, thanks for the info. I guess I was trying to figure out whether VII's in the ATF is good or bad. So if the modern VII's don't have much shearing trouble in ATF's then I guess it probably doesn't really matter if the ATF has VII's, except maybe it will be a little thinner at cooler temps which might give more fuel economy and maybe better shift feel until warms up.

-Louis

 

[MolaKule]

Generally most formulators start with a 4 or 5 cSt mineral oil and add good quality VII's (which bumpp up the viscosity to about 7.5 cSt) and which are good for maybe 30,000 miles.

For all of our current ATF's, we start out with XX cSt PAO's and esters and put the addpack in (minus VII's), which tends to thin it to about 7.6 cSt. We prefer to make the VI be controlled by the fluid, not the addpack.

BTW, most 7.5 cSt (average) ATF transmission fluids will shear down to about 5 cSt over 30,000 miles; even synthetics.

 

[bruce381]

"Generally most formulators start with a 4 or 5 cSt mineral oil and add good quality VII's (which bumpp up the viscosity to about 7.5 cSt) and which are good for maybe 30,000 miles."

I shoot for 7.8-8.0 which will help stay in grade >6.8 at least 20K.
bruce