PS fluid Thick or Thin?

[wander2039]

Over the last couple weeks i've done a partial power steering flush on both of my vehicles. One the Escape I used the generic Mercon from AA, the Ranger I used some leftover Synchromax. On both the steering was stiffer more so on the Ranger. In my opinion the Ranger's power steering was a bit to assistive to begin with. The Ranger only has 6k on it so the fluid I pulled out was new, and from pouring in the containers it seemed to much thinner than regular Mercon. Not a good test so I don't that for a fact.

On RP's website the Synchromax properties are:
cSt @ 40°C 35.3
cSt @ 100°C 7.7

RP's powersteering fluid:
cSt @ 40°C 45.0
cSt @ 100°C 9.0

RP's ATF:
cSt @ 40°C 32.4
cSt @ 100°C 7.4

On the Ranger the powersteering pump was a bit noiser overall, only noiser during stopped turns in the Escape. That's what worries me.

So the question is thin or thick better for powersteering systems?

 

[Steelhead]

Mobil 1 Syn. ATF made my Ford power steering which is spec'd for Ford's pwr steering fluid smoother, quieter and far less volitility fluid level drop...did a full complete flush/change out the return line off the reservior with front off ground....added an inline filter and larger cooler

most of Ford's pwr steering systems operate at 1200 psi+ and 250d F+ in southern climates w. urban driving, far higher pressures and temps than auto transmission...real killer of the fluid
cSt @ 40º C 34
cSt @ 100º C 7.6

[ September 13, 2006, 09:47 PM: Message edited by: Steelhead ]

 

[gtx510]

I'm guessing thicker fluid would make for more pressure in the system and the steering would feel lighter (more power assist).
And it'd quiet a noise pump better.

 

[unDummy]

Thicker seems to make my PS pumps sound better. It might also help with tired or worn pumps.
Go thicker if you want quiet over cold performance. Thicker is not better during those cold mornings(belt squeal). But, using a synthetic should more than make up for the cold.

Thinner costs less HP and might be better for a pump in good condition.

Flow is just as important as pressure. Poor flow from an overly thick fluid might not be good. This might be something that you're experiencing, reduced flow from thicker fluid.

Also, syncromax isn't blended for power steering fluid usage.

Redline has power steering fluid and ATF also.
And, the exotic Pentosin is on the thin side.

 

[wander2039]

If thinner is better why is RP's power steering so thick? To me thinner would be better, comparing the 5w20 debate. Unless the cst doesn't matter and it comes down to additives. The ps fluid does have a lower VI number though.

A cooler and filter is a good idea but with my small vehicles i'll just change it out more often. The 00 5.4L had a powersteering cooler and never had any problems with it. I think I might shoot RP a email.

 

[MolaKule]

Thicker (9.x cSt) is the preferred viscosity for racing since it thins out less in racing due to higher under hood temps and constant steering manuevers; keeps the steering feel contstant throught the race.

ATF is specified for most PS' in daily drivers because of its low temp properties.

 

[tdi-rick]

quote:

---

Originally posted by MolaKule:
Thicker (9.x cSt) is the preferred viscosity for racing since it thins out less in racing due to higher under hood temps and constant steering manuevers; keeps the steering feel contstant throught the race.

---

and add heavy off-road use to this. This will overheat and foam the fluid possibly more quickly than heavy track use.

 

[wander2039]

RP making the ps fluid thicker makes sense in way since it's geared towards the racing scene. I'll stick with the ATF blend for now.

 

[kilou]

The PS oil recommendations for my Volvo are ATF (type D,F or G) or Pentosin CH11S. I looked at the specs of those fluids and the differences in viscosities are huge!!!

cSt@40deg / cSt@100deg
Pentosin: 18.7 / 6.0
ATF: 43.2 / 8.3

How is this possible to have a so big difference??? I've been using ATF in my PS all the time (done 260,000km) with no problem either summer or winter. But I wonder if I should change to Pentosin. Do you think Pentosin would be better for my pump (especially in winter)? What about the seals, would these leak with a so thin oil?? I wonder if the pump would be as well protected as with the ATF too???

 

[unDummy]

Most fluids shear down. Starting with a stout thin fluid is not more of a problem then using a wimpy thick fluid that thins out.
I don't see leaks being caused by the fluid vicosity. A seal will leak when it is bad and needs replacement.
If you look at SAE-J300(yeah I know its a motor oil spec), the 20wt oil range is 5.6-9.3. Most(all?) ATFs and PSFs fall into that 20wt range.

Pentosin CH11s is one of the best 'all weather' PSF's out there. Use it if you can afford it and have a supplier for it.

 

[gtx510]

I think Inter Auto Parts carries the Pentosin ATF and power steering fluid. I'm pretty sure they have the brake fluid and coolant too. They also stock MB coolant and ATE brake fluid.