I have 90' Jeep cherokee with 4.0 I6. About a week ago it overheated on a 2 mile trek from home. The serpentine belt jumped off during this overheating. When I checked water pump,bearings seemed to be shot. Below is what I replaced.

water pump
thermostat
serpentine belt (since I had it apart)
Overflow tank and cap
radiator hoses

I burped motor thru the temp sensor on back of block and it still overheated. I checked clutch fan to see if it would spin after motor was at operating temp and it is nice and tight as it should be.

As I drive on the highway it heats up to normal temp of 210. As soon as I exit into city traffic temp increases almost to red in a few blocks before I shut it down.

When first started overflow tank is a little under half full. It gets to the point where it builds so much pressure it fills overflow tank up and starts to leak out of tank.



Help Jeep family!!!!!

 

Im not if this applies to your year jeep but my 88 that i had theres a metal spring that sits in the lower hose on the water pump side which prevents it from choking itself from coolant

 

When first started overflow tank is a little under half full. It gets to the point where it builds so much pressure it fills overflow tank up and starts to leak out of tank."
Start with a compression test.


"I checked clutch fan to see if it would spin after motor was at operating temp and it is nice and tight as it should be."
Not a realistic test, for a measly $30 just replace it if the motor isn't trashed.

 

Yes and Yes. As old as your XJ is flush the system "Very Well" including the heater core and for a $100 just replace the radiator as well cheap and a good idea from an upkeep point of view also.

 

What do you think the chance is that the motor might have been damaged during first overheating? Ive never let it get to the red on the gauge, but I was talking to one person that thought because the cooling system was building up so much pressure that I might have damage my motor somehow.

 

That spring has mystified me for years.
Cruiser54 mentioned that it is only there for factory building process, to prevent collapse when a machine fills the system. Not necessary thereafter.

 

I had a guy tell me to do the fluid test that shows if you have exhaust gases in my coolant. Which I dont have a problem doing. I guess because I never let it get to the red that I'm hoping no damage is in the head or anything. It seems to run perfect (other than overheating). No coolant in the oil or sweet smell or anything.

 

I never noticed the spring when I pulled off the lower radiator hose to replace the water pump. I'm not sure if I have one in there or not. My gut tells me Ive got air in the system and lack of flow, but I'm not familiar enough with the 4.0 motor to be sure.

 

Everyone gets so hung up on that spring in the lower hose. It doesn't matter if it is there or not.

 

I guess I'm starting w flushing the system with the prestone fill n flush kit

 

According to the guys on this forum, my motor should be dead with the amount of time I've let it run too hot. But that inline 6 keeps chugging. Maybe it'll die tomorrow. Still runs great now though.

 

That makes me feel better.

I just drove home (5 miles all highway). stayed right around 210. I excited the highway and went thru one light, maybe 1/2 a mile and I was almost in the red. What really getting me is that I popped my hood and the overflow tank was swollen up like a balloon. How/Why is it building so much pressure so quickly?????

 

Regarding yhe mysterious spring,I've heard both that yoh need it and that you don't. ....if i took it out i would put it back in

 

Well I just flushed the system w the Prestone setup. Filled it, burped it and let it idle for about 25 mins. It got up around 210/212 and never went above. The real test will be driving home and seeing how it does. What baffles me is that my coolant level in overflow always increases to the point of over expansion.

 

Get a new brand name radiator cap (12 lbs) and report back....