After 16 years and 216,000 miles I replaced my power steering pump on my 94 SR5 truck with the 3.0. In doing research for this, I learned I should be been using ATF and not PS fluid. Yes, I know now it's on the cap. It didn't seem to affect it though. With the new pump, I did my best to purge all of the PS fluid from the system and replaced with Dextron ATF. After much bleeding most of noise went away. After a short drive it is making noise again and the pump has a slight vibration. I am wondering if I did damage mixing dissimilar oils.

 

Shouldn't have caused an issue.

Sure it's the pump making the noise?

Did you get all of the air/air bubbles out?

If the pump, your replacement may have an issue...

 

Dissimilar oils shouldn't have caused any issues, except maybe for the very slight possibility that an internal bearing failed. But that would tell me that it was a cheap rebuild in the first place. Or that the shaft/pulley mate is weak/loose.

I've run mine with ATF and P/S fluid mix for 75,000+ miles. Still fine. OE stock pump

 

What kind of noise? Is it screeching? Could be your bearing on the belt tensioner or what of the belts. Can make a similar noise to a power steering pump going out.