PSF viscosity indexes?

[dailydriver]

WHY is there such an extreme range in the various power steering fluid VIs (i.e.; RP=177, RL=143, Max Life=95)?

Is it ONLY due to some using superior basestocks, or are they loading it up with VIIs as well (and if so, are they the "good" PMA VIIs?)?

Need one be as concerned about the VI of PSF as one should be of motor oil?

 

[dparm]

I would argue no, because it doesn't undergo wild temperature swings.

 

[GMorg]

PSF can easily reach 160C and under off-road conditions, lots of curves, or driving in a cross-wind, PSF can exceed 200C. Although these temperatures don't come close to cylinder walls, the temperature swings on PSF is very similar to motor oil. The big difference is that oil goes from ambient to operating temps in a fairly predictable way. PSF temps are much more dependent on driving conditions and ambient temps.

The big issue is that the driver can feel PSF viscosity extremes as "morning sickness" or "steering fade". The average driver cannot notice most swings in oil viscosity. There is reason that some systems have PSF recommendations for fluids with VIs in excess of 250 - drivers can notice the difference.

 

[mechtech2]

Originally Posted By: dparm
I would argue no, because it doesn't undergo wild temperature swings.


You know better than that!
PS fluid gets HOT!Even with factory coolers.
From -10F to 200+F.

 

[rslifkin]

PS fluid can certainly get hot, especially in vehicles with hot engine bays.

I put a factory trans cooler (11x5" stacked plate) in the PS return line as a cooler after a day of towing (about 8 hours, and some tight maneuvering) in 75* weather, where I cooked the fluid so badly that the white bottle Valvoline PSF that was in there was dark, nasty smelling, and obviously sheared to heck (judging by a bit of pump whine and funny steering feel, which was corrected after changing out the fluid).

Even with the huge cooler, in normal daily driving, the fluid still gets noticeably hot (feels to be around 130 - 150 F reservoir temp, compared to a scorching 200+). It still gets far too hot to touch under heavy towing, etc, but I haven't gotten it hot enough to cook the fluid again.

I've noticed in the past that the steering feels a little heavy on cold winter mornings for the first couple minutes of driving (haven't been through a winter with the cooler yet), so a fluid with a high VI would definitely be good for most systems.

 

[dparm]

Originally Posted By: mechtech2
Originally Posted By: dparm
I would argue no, because it doesn't undergo wild temperature swings.


You know better than that!
PS fluid gets HOT!Even with factory coolers.
From -10F to 200+F.



Yes, but not 300-400F+ like oil would in a bearing, for example.

 

[dailydriver]

Thanks for the replies.

Does anyone know which currently available (full synthetic/boutique) fluids have a higher VI than the Royal Purple Max Steer??

 

[DWC28]

You need to also consider other factors beside VI. Honda uses a heavy PS fluid while most others use a lower viscosity fluid. Durability or resistance to change over time is also important as many PS fluids are filled for life. VI in a fluid can change rapidly over time, so new VI may not be close to used VI. Pentosin has a 300 VI product.

 

[GMorg]

Pentosin CHF 11s has a VI of 313. The non synthetic version, CHF 202, has a VI of 302. Champion Honda/Acura fluid has a VI of 230. That are several others that have higher VIs than RP EZ.

 

[dparm]

Swepco says their 715 power steering fluid has a "high VI parrafinic basestock", but they don't publish the figures.

 

[GMorg]

Mag1 Premium PSF has a VI of 172 and claims to meet or exceed the following OEM specs:

Acura/Honda PN 08206-9002 PE, GM 9985010 Saginaw Power Steering System, GM 9985835 Wide Temperature Performance (Synthetic Multi- Temperature), Chrysler MS 1872, Chrysler MS 5931F, Ford M2C138-CJ, Ford M2C33-F, Ford M2C128-C and D, Audi PN G002000, Mercedes Benz PN 00 989 8803, Saab PN 30 09 800, Subaru PN K0Z09A0080

http://www.mag1.com/ProductDetails.aspx?id=e49fa11b-4f1e-413a-9797-30dd6e46c899