Still searching but wanted some opinions on what has worked for you. My issue is a rpm related pump whine when hot. Will throw some Lubegaurd additive at it for now then change fluid then change pump in that order- have had this or that issue with my system for years. 89 chev k1500 Saginaw with hydroboost, trans cooler on this system. I am using a u-joint vs rag joint so that will contribute to some noise. I have thrown many pumps at this issue and am considering a good used GM unit now.

Lived in northern Canada where keeping PS systems and hoses happy is a challenge- found Acura fluid worked very well.
- on a dyno tuning session the M1 ATF blew out the pump pressure cap, what a mess.
- Amsoil swelled cap seal
- using Redline (with some Ford friction modifier) now with a above mentioned whine.

Looking at a fluid I can buy by the liter or jug some of which are hard to source here.
- LiquiMoly
- Driven
- CHF 202, I have had good luck with Pentosin products in the Honda manual trans.
- CHF 11S
- Febi/Bilstein (part number?)
- Idemitsu (not liter size)
- Ford XT-5
- Lubegaurd seems overly expensive even compared to the above.

I think your seeing a German trend here So....I welcome your thoughts.

 

NO fluid will ever NOT do what you are complaining about. The fluid IS NOT the problem no matter how many kinds you've tried or what you've convinced yourself of. Take a step back and THIMK about what you've learned by messing with 50 different brands of fluid, all of which did THE EXACT SAME THING.

You have a leak.

If ANY kind of fluid "blew out the pressure cap", the ONLY POSSIBLE reason for it is because the system got air into it. A leak on the return side ALWAYS allows air in at certain times. Then, when there are bubbles of air in the fluid, the slightly foamy fluid goes through the pump and gets pressurized; and then when it returns to the reservoir, where it is under NO pressure (atmospheric), it IMMEDIATELY bursts into a fizz, just like shaking up a hot 2L of Diet Coke and suddenly taking off the cap.

Fix the leak(s). Return hose, pump-to-reservoir O-ring, & pump shaft seal are basically the ONLY things that can cause this. The O-ring is particularly insidious: if someone, perhaps some PO, pried on the reservoir body to tighten the belt, then it is distorted, and RUINED. The O-ring then cannot possibly seal.

Best to just replace the pump WITH RESERVOIR INCLUDED and return line. As cheeeeeeeep as they are, no other alternative makes sense. In case you're the one that is distorting reservoirs, learn how to tighten the pump without damaging it.

Then use any kind of fluid you want. The parts store brand stuff works fine. No need to line somebody's pockets for something that probably isn't any different to begin with.

 

Serpentine system- no prying needed. I'll revisit hoses.

 

On top of what sofa mentioned, I've been partial to actual GM power steering fluid. Just seems to work the best. Purchased at a GM dealership over the parts counter.

RBob.

 

- Current fluid does not seem to be aerated.
- I got away from the normal fluid up north as the hoses would burst (common issue not just me, oem would last a few years then aftermarket were one a month until I had hydraulic hoses made). But I'll consider it. The ACD fluid off the net is not the same formula?

 

Interesting issue with the burst hoses. I guess the P/S fluid gets too thick in the cold.

As far as the ACD fluid mail ordered being different, I don't know. Too much counterfeit stuff out there to be sure.

RBob.

 

Many years ago, I did engineering work on Hydroboost units. Power steering / brake systems with Hydroboost are very good systems, but have some additional sensitivities from standard ones due to the load on the hydraulic system from the Hydroboost unit. Often they have a larger capacity pump to handle the additional flow demand. It isn't obvious, but there is flow demand due to internal leakage even when the brakes are released. That leakage is returned to the reservoir by the third hose on the Hydroboost unit. The particular area of concern is the pressure regulating valve. It is a spool valve and is extremely sensitive to the clearance between the valve and the bore. Excess clearance can cause high leakage back to the pump. High leakage can cause elevated flow that may cause your noise to be worse.
Based on what you are saying, I expect you have a cold weather viscosity problem driving high cold pressure, but if you choose a fluid that is too thin when hot, your leakage rate may be too high causing more noise. I can't comment on your fluid list, but you might look at the published specs for viscosity cold and hot for each one. GM sells a cold weather fluid that is at least partially synthetic that might fill this need. If that doesn't help, it is also possible that your Hydroboost unit has excessive wear in the valve bore area and you may need to replace the unit.