Discussion about viscosity

[FowVay]

I am looking for a modern replacement for Texaco ETL-7045E that was first fill in my old BMW A5S360R automatic transmission. Castrol Transmax DEX/MERC has caught my eye for being nearly identical in typical test data. My one concern is regarding the Brookfield viscosity at -40ºc. How critical is it to have this viscosity closely match the original fluid? The ETL-7045E has a dynamic viscosity of 17,500 cP at -40ºc. Some of the oils I've considered, including Dexron VI, have dynamic viscosities of only 10,000 cP. How would this affect the transmission and the shift quality?

Any discussion?

 

[kschachn]

Isn't that fluid just another Dexron III type fluid? If so, then you can use Dexron VI as a replacement. Or Maxlife. Or Mobil 1 ATF.

I've been using Supertech Dexron VI in my (old) BMW for over 100,000 miles now and it is working fine. Not the same I realize but if the Texaco is Dex III then Dex VI is going to work. The viscosity stability of Dex VI is better than the old Dex III so even though it may start off lower, it won't get reduced as much as the Dex III would have.

 

[slacktide_bitog]

Dexron VI is more shear-stable than Dexron III. So even though its starting viscosity is lower, the ending visc after being put into service will not be. Plus, most Dexron VI ATF's are full synthetic, or at least use a better quality base stock than the old Dex/Merc fluids. You will not have any problems.

Also, Castrol's full synthetic ATF is the same price as the regular Dex/Merc at AAP this month, 2 quarts for $11

 

[FowVay]

Things I notice different about the 7045E is that it has a very high viscosity index compared to Dex III, the viscosity is much higher with Dex III in comparison to Dex VI, pour point and Brookfield dynamic viscosity is also higher.

This stuff is a Dex III on steroids and I'd like to get something similar without tracking down the Texaco fluid at $20/liter.

 

[userfriendly]

Have a look at Delvac syn ATF or Chevron's synthetic HD, both meet Allison TES 295 and many Euro specs as well.
In Canada Pet-Can Dura drive covers most of the Euro specs.
None of these fluids are exactly for the budget minded, but you get what you pay for.

 

[kschachn]

I honestly don't think it will make a speck of difference, especially if you confine yourself to using a synthetic or synthetic blend ATF. I have a friend who has a 540i and that specs the unobtaium LA 2634 fluid, he uses Mobil 1 ATF and has for years. It hasn't grenaded yet, I think some of those old specs were there just to keep the owner from using some cheap fluid.

 

[901Memphis]

10,000 cP @-40C is a better value than 17,500, the 10,000 means its thinner at lower temperatures so it flows better in cold

 

[A_Harman]

Originally Posted By: 901Memphis
10,000 cP @-40C is a better value than 17,500, the 10,000 means its thinner at lower temperatures so it flows better in cold


That was exactly what I was going to say! The lower viscosity in subzero temperatures will improve shift quality.

 

[FowVay]

That was my impression initially about the cold flow properties but even at 17,500 cP's at -40ºc, this stuff still has a pour point of -51ºc. This Brookfield test is sort of like comparing the HT/HS viscosity of motor oil. Some cars are specified for a lower HT/HS (3.0 cP at 150ºc) and some specify the higher >3.5 cP. This is not done because of fluid quality but rather because it is a performance design quality.

According to Mobil, their Mobil-1 ATF has a Brookfield viscosity at -40ºc of 10,050 cP and yet it has no better pour point (also -51ºc) and has a much lower viscosity index (176 vs 194).

As it looks, the Castrol Transmax DEX/MERC is a very close replacement to the Texaco fluid and might be what I use.