I had to replace the water pump on my '89lx today so.... I also replaced the thermostat and the radiator hoses. I also went ahead and replaced the timing belt since I have no idea when it was last done. But now, I have a whine coming from the engine, sounds like from under the timing belt cover. To get the belt cover off I had to take off the serpentine belt idler pulley. What's the torque spec on that bolt that holds the pulley to the idler body? Can you have the timing belt to tight? The spring for the timing belt idler pulley didn't have enough strength to push the belt tight so I helped it into place then tightned down the nut.
I would check the pulley on the serpentine tensioner first, if that's what you removed...I don't know what the torque spec on that is, but when I replaced mine I just tightened it as much as I could. Also make sure that neither belt is rubbing against anything, there's a chance that the timing belt could be up against something and causing the noise.
Update: I got around to taking the serpintine belt back off and ran the engine for a few seconds. Turns out the new belt (Napa) is rubbing against something, both edges of the belt are worn down to the threads all the way around. Pulley to pulley alignment looks pretty good but not great, I've seen worse though. The power steering pully / shaft can be pulled in and out probably more then it should. The problem is, I threw away the old belt. I do remember that its edges didn't look like this though. Update 5/20/06: I found the old belt and sure enough, the edges are ok. I put it on the car and the whine is still there. Now I don't know if it was there before and I couldn't hear it because the muffler was to loud or if the new Napa (rebuilt) water pump is whining.
I found some water pump 'anti scale/lube' at napa. After 50mi the whine has 'greatly' decreased. I'm crossing my fingers.
