mrlmd

In the last day or two my car started to make a low-pitched whirring or whining sound when I turn the steering wheel so I checked the level of the power steering fluid and it is low (doesn't even register on the dipstick after you wipe it off and reinsert it, but it was wet when I originally pulled it out). I assume the noise is related to the low volume of the fluid, the steering is fine and seems normal.
The recommended fluid is GM Power Steering Fluid, but is there anything else that is used? I assume it's different than the GM recommended Automatic Transmission Fluid, some of which I have. I hate to make a 40 mile trip to the stealership and pay their prices when I can go to the local Walmart or NAPA store or Autozone or Advance and get something compatible for far less money.
And I have no idea where the fluid went, here is nothing dripping underneath my car or anything dripping down on any hose etc. in my engine compartment. I have a 2000 A4 coupe I bought a little over a year ago, now with 81,000 miles, and I never checked that, so who knows how long it has been low.

American Heritage

The fluid went somewhere. You need to find the leak.
you can use regular power steering fluid (prestone, lucas there are a few others). I think most parts stores carry the prestone (yellow bottle) that will work. If your looking for a higher quality P/S fluid then you can order some Redline.

motoman250f

the fluid is likely in one of the boots on the side of the rack and pinion. they will fill up and hold oil when the seals leak. the rack may need replaced

Cybermind

You can get Valvoline PS fluid which meets the GM spec. Walmart has it. It is an excellent PS fluid.

I agree with the others. You have a leaking PS rack and it probably will need replacement, eventually. But, how quickly will depend on how big of a leak you have.

strand rider

I don't know, (key phrase) about power steering fluid, but have always heard that in transmission fluid, interchangeable in many applications, only mix the same brand or leave it alone, the key being different effects on seal expansion.

I know that fluid specifications are the only sensible key, but my car has some wear and might not accept another fluid as well, even though they spec out the same. It makes little sense on the face, but hydraulic systems can act funny , mine is far from new, and driving is more fun than fixing.

Paranoid, brainwashed by transmission advice, I don't know. But my steering rack was a little wet last time I looked, so I decided to be as conservative as possible as spend four bucks down at GM.

Cybermind

You are correct when it comes to automatic transmission fluid. It is prudent to stick to OEM and not mix different brands. But automatic transmission fluid is much more complex as is the transmission itself. The viscosity and lubricity level is critical and no two manufacturers have the exact same properties.

Power steering fluid is just a hydraulic fluid with seal conditioners and is nowhere as complex as tranny fluid. Different brands can be mixed without any issues as long as they both meet GM specs. Yes, sticking with GM power steering fluid is a no brainer but I can guarantee you that it has changed in the last 10-15 years and is probably no longer the same fluid as factory fill anyways.

There is one practice that I advise against and that is using automatic transmission fluid in the power steering system. C5's are not old Buicks and our steering systems are pretty complex. They deserve proper fluids.