hi. I own a 99' SS Convertible. sub 50k miles. I started having problems with my power steering (pump I thought) groaning and grinding when sitting in a drive through or parking lot. Once I would get back on the road and up to speed the sound (and feel of the strain through the steering wheel) would lessen and go away. Took it to a shop and they replaced the power steering pump. First thing out of the box we noticed that it was different. There are only 2 bolt holes to attach it with compared to the 3 of the stock piece we pulled off. We confirmed with the parts store that it was the right part, put it on and it was fine for about 3 weeks. Then it started doing what it had before. Thinking maybe the brand was a bad choice I ordered an AC Delco remanufactured part for twice the price of the first. I took it to the shop and we started replacing it. The fluid that was in the system was almost a chocolate milk, foam consistency. So we flushed and replaced all the fluid. Now, 3 weeks after replacing it, it is starting to do the same thing. When it gets warm, or whatever its doing, while I am in a parking lot or drive through, fluid starts leaking out of the top of the reservoir. If its driven and not in a parking lot this does not happen. I have replaced the cap thinking it was a bad seal letting air in but its still doing it.
I am at a complete loss as is the mechanic. Is the pump just not made for the 17" 275/40 stickies? Why does it only act up when I am in a parking lot or drive through? Anyone at all seen something similar to this? It is driving me nuts.

 

Do you have a power steering cooler in your upper radiator hose?

 

I was thinking the same thing, cooler gone bad and letting a little coolant get into the PS fluid.