My 1988 F-150, ~100,000 miles, 2-wheel drive, 4.9L I6, 5-Speed Manual needs a new radiator and heater core. I am thinking of replacing the water pump at the same time. Is there anything special I should know about replacing the water pump? How do I remove the pully? Should I just leave it alone since it is not leaking (yet) or go ahead and replace while I have the radiator out? Knowing my luck, the day after I replace the radiator the water pump will go bad.
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I wouldnt touch it. I have seen em go 200+

 

I second that,if it's not broke don't fix it.

 

X3. And only use distilled water w/ antifreeze.

 

I would just pull the fan and the pump and see if there is any backlash in the pump axle, if there is'nt it's a good chance it's still good.
And don't forget the antifreeze just as ymeski56 wrote.