Car: MINI COOPER S 2002:
At 56,000 km an independent service mechanic replaced a Power Steering line, bled the original PS fluid and re-filled using Amsoil ATF.
The MINI PS fluid cap and MINI Spec states: Use only Pentosin CHF 11S
I drove the car for 1.5 years (mostly non-winter driving)for a total of about 10,000 km with the Amsoil ATF. I did not notice any problems until recently in -25 degree Celsius, when I noticed an issue with PS assist and a high-pitched whine in my PS pump (which goes away when the outside temp is -10 degrees Celsius.

Question: Do you think the Amsoil ATF may have caused damage to the Power Steering Pump? And/or the PS Rack? Both are expensive repairs. I have been advised by MINI to bleed the PS Amsoil ATF fluid ASAP, replace with Pentosin CHF11S and see how the pump and steering system responds, and try this a couple of times (to avoid potential issues about mixing the two different fluids and risk causing seal problems). The independent mechanic is willing to do this. I am looking for any further advice on:
a. Comments on the key differences between these two fluids?
b. What the likelihood of damage, if any, might be using the Amsoil ATF instead of Pentosin CHF 11s? (esp to the pump and/or steering rack – both of which are expensive to replace)
c. What is the best course of corrective action?


[FONT=Arial]1. Mini indicates on the PS cap: USE ONLY CHF 11S (Pentosin product)[/FONT]
[FONT=Arial]- dark green[/FONT]
[FONT=Arial]- density 825 kg/m3[/FONT]
[FONT=Arial]- Viscosity[/FONT]
[FONT=Arial] 100Deg: 6.0 mm2/s[/FONT]
[FONT=Arial] 40 Deg: 18.7 mm2/s[/FONT]
[FONT=Arial] -40DDeg: 1100 mm2/s[/FONT]
[FONT=Arial] [/FONT][FONT=Arial]Vis[/FONT][FONT=Arial] Index: 313[/FONT]
[FONT=Arial]2, Amsoil ATF[/FONT]
[FONT=Arial] - red[/FONT]
[FONT=Arial]- density: ?[/FONT]
[FONT=Arial]- Viscosity[/FONT]
[FONT=Arial]100Deg: 7.6 mm2/s[/FONT]
[FONT=Arial] 40 Deg: 38.9 mm2/s[/FONT]
[FONT=Arial] -40DDeg: 9800 mm2/s[/FONT]
[FONT=Arial] [/FONT][FONT=Arial]Vis[/FONT][FONT=Arial] Index: 168 [/FONT]

 

Sure it is possible, but I know of no way to tell for sure.

If it was mine I'd have the Amsoil ATF flushed out with fresh CHF11S. Hopefully that will make things better.