i have had this problem for about a week, dont drive far so havent been to worried about it but now that its the weekend i gotta get it done, so heres the problem, when the truck is running it doesn't leak a thing, but as soon as i shut it down, it just pisses out. any ideas? i bought the gasket to be safe and cheap, but if i do need the pump ill get it, TIA Vince

 

look for the tell-tale drip from the bottom of the water pump's fan pulley. this is a good sign the seal has worn out, which is sort of normal. my 01 went out at about 120k.

seal itself is not replaceable. you have to replace the entire pump.
our pumps are aluminum, which led me to buy a 'new' pump rather than a 'rebuilt'.

the reason you get such a big leak after you shut off the engine is 2 reasons.
one is that the engine actually gets hotter for about 15 more minutes, which increases pressure in the cooling system.

the second reason is that when the engine is running, the leak is minor and it sort of slings around and evaporates. with engine not running it just sort of pisses out.

as long as you keep it FULL of coolant, you can drive it for while if need be.
when you do replace the pump, its a good time to replace timing set, fix leaking plenum, front seal, etc.