Jeep over heating problem

Papa_Jon

Papa_Jon

non speller
Joined
Jul 27, 2007
Location
China Grove
2000 xj 4.0
New radiator, new hoses , 2 new t-STATS, new electric fan , new cap, flushed entire system 3 times.
After about 10 mins of driving or 15 mins of idle it reaches 220 , before I turn it off. Fan comes on at 213. Building alot of pessure even with out a T-stat install it boils out coolant tank and cap.
I checked coolant for bad head gasket or cracked head test showed no signs . Water pump looks fairly new .
Need help trying to get it ready for son to go back to school
 
If you have an IR thermometer, take the temp of the upper and lower hoses when the jeep is warm and running. That'd be a good indicator.
 
Nothing to add, but Lina was asking how you have been doing lately. I told her we are not girls so we don't keep up like that!
 
I meant to check the difference between the top and bottom hoses. If the water pump is bad, the differential will be much higher.
 
The top hose should be higher. I don't know about the 4.0 in a cherokee, but based on other systems I have worked with 8-10 degrees F is a pretty good estimation. If the differential temperature is much higher than that, lets say 15-17 degrees F, then you have a low-flow condition in the radiator; since you have replaced the radiator, hoses, thermostat it would be fairly safe to assume none of them are blocked, pointing to the water pump as the next most likely candidate.
 
Some of those water pumps have a composite impeller and are know to break. I just went through this on a good I bought and was told it had a bad head gasket. Replaced gasket and all hoses and then found no coolest flow. So in short check the water pump it is easy to do and if it is good only cost is time and a$2 gasket. Just my. 02
 
Those 4.0 engines of that era are known to have crappy cylinder head castings and are known to crack. When they do, they'll consume coolant and introduce exhaust pressure into the cooling system.
Your symptoms sure sound like a head issue to me. I wouldn't be against removing the head and having it magnafluxed personally.
With a failure like this you will not see coolant in the oil or vise versa.
 
Could the passages in the block be clogged with garbage and restricting flow? How bad is it to pop a freeze plug or 2 out?
 
Something is building excess pressure. Can't be many things aside from combustion gasses. I've been the victim of a combustion detection tester that did not indicate gasses. It was on a late model XJ with a 4.0 coincidently.
 
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