i had the same prob. the only thing to do to eliminate this is converting to the 92 open system, it cost me about 300 bucks and a knowledgeable mechanic. otherwise your going to spend all your money replacing parts that dont even cause the prob, good luck

 

do we have any leaks in the system?
do we have good flow in the system?
Is it boiling over overheating?

i had one in my shop about two years ago that i ended up replacing a head cause the moron drove it with a KNOWN bad water pump.. the impeller blade rotted completely off!

 

that sounds pretty thickheaded. yeah everything was running great had the old system and every three months or so i had to change the pressure bottle but now while converting i ran into a thermostat housing lower threadbolt hole problem, it was stripped so i had to get a 21/64ths drill bit and tap and some loctite and tommorow we will see if it holds. cross my fingers because as much problems as this jeep has given me with the cooling system, i just cant see myself wanting to drive anything else. i love my piece of crap jeep!!!