Use the Paul Nimz method of power steering fluid change. The first step is to slowly replace old fluid with new to help clean off the soft to medium deposits. Crap that would just dirty up a complete fluid change right away. It goes something like this:
Get cheap type F (or whatever your manual specs. My '89 specs Type F) ATF. I used Walmart supertech at $1.27 a qt or so.
Suck out the resevoir, my 89 holds about 12 oz. I use an old turkey baster. Then fill up to the full cold mark with the fresh, clean, and cheap Type F. Repeat every other day for a week. Then start doing the same thing every 4 days or so. Then after a week or two of that switch to doing it once a week. After about 3 or 4 quarts of cheap stuff I bought a couple quarts of high quality conventional Type F: Castrol. About $2.69 a quart at autozone. So, I'm going to swap that in a la turkey baster whenever I think about it as long as some mileage has accumulated. I would probably be fine if I just left the castrol in there. The fluid has stayed clean even before I started with the Castrol. But what I'm going to do is:
When I get the last 12 oz out of the second bottle of castrol then I'm going to add an oz of auto-rx to the power steering system and drive that for 1000 miles. Then I may or may not turkey baste fluid out for a week or so depending on if it looks clean or dirty. Then I'll drain the system completely and replace with Redline power steering fluid. I called Redline up and they said it would be just fine in a system that requires Type F. Then I'll add another 1 oz of auto-rx in the system and forget about it. I might put a filter on there, I don't know. They're cheap, but I'm lazy.
You know, when I mentioned the Paul Nimz method to Frank he said he was glad I brought it up. Frank had just spent a good chunk of change getting his powersteering system purged with a fancy machine. I forget how much time had passed, it wasn't much, and Frank said that his power steering fluid looked black again. This is what the Paul Nimz method aims to avoid. Frank's going to give that method a try next time.
