my 90 cherokee with the closed system keeps overheating. I have only overheated it badly once at first my e fan wasnt turning on and I found that to be a bad fan switch so I have it wired together to keep it on until my new switch arrives, but that didnt fix it so I put a new thermostat in today and flushed my radiator out as well. then I filled the rad with the upper hose and drilled a little hole in the thermostat to let air escape filled it up let it idle and it started going toward the red so I shut it down. My overfull tank has a pin hole leak also.

I pulled the spark plugs and chenged them to make sure I didnt blow a headgasket and they all came out dry but 2 of them have air bubbles coming out from where water was sitting next to the holes from filling the hose but I dont think I have them in tight enough is the problem. The upper hose is hot at the T-stat but cold at the radi so I'm thinking my water pump failed but I would like addvice to make sure I'm going the right direction. The radi is clean and looks to still be in good shape with no leaks.

sorry for the long post but this is my daily driver so I need it on the road quick

Sounds like a water pump to me also but i do have a heat gun to double check the temp if you want

Have you burped the system?  4.0 are noted for need it especially the closed systems. Good article at

http://www.lunghd.com/Tech_Articles/Cooling/BurpAirMod.htm

I added the flush kit adapter to mine, it was the easiest.

Also think about a fan override circuit I did this on a Pontiac Turbo that constantly ran hot.  Its a pretty simple circuit using a Bosch relay.

I could email you a word doc with schematic if you like.  Can't seem to be able to add a doc to these posts

yeah I changed the pump and burped the system its not overheating now but I have to wait until I get a overflow tank and my fan swtich to complete it, because my little hole turned into a huge crack.