The fan clutch and fan are threaded onto the pump snout. You need either a large adjustable wrench, the proper sized open end wrench, you can rent a proper fan clutch wrench at many parts stores as well if you don't have anything that fits. Remove the upper half of the shroud, remove the belt, unscrew the fan/clutch assembly. Remove the bolts holding the pulley to the pump and R& R the pump. Reverse the procedure.
When you fill the cooling system park the truck with the nose uphill and turn the heater on max. Then fill it and run it to warm it up, let it cool and top it off. That should prevent an air bubble in the cooling system.
If I may ask why are you replacing the pump?
October, 31, 2010 AT 11:20 AM
I have the same problem on my 1997 Blazer, trying to get the fan off the water pump so I can replace the pump (it leaks and is the original, 135K miles). I have a big enough wrench but it just won't come unscrewed even when I keep the water pump shaft from moving. Is there a trick or could it be rusted shut? It's not left-hand threaded, is it?