warthog

I have had a thread about this before but not with this much detail.

it a 98 4.0L

here is whats going on. the temp in my xj is right around 210 to 215 normally but sometimes when i am just poking around off road or in really slow traffic. all of a sudden the check guages light will come on and my temp will shoot up to around 250 to 260. then after i shut down, turn the key back on after 5 minutes or so the guage is still at 250-260 but then comes back down to 215 or so. the first couple times this happened i thought it was just a sensor or eletrical problem because i didnt think the coolant could heat up and cool down that fast. but this last time when the guage went up i actually opened up the hood (after burning my hands) and it was boiling. i have the radiator cap that you can release the pressure. so i released some of it then my overflow tank started overflowing. the previous owner told me he replaced the water pump, radiator and hoses. i am going to call him back and confirm soon. i have replaced the thermostat and the radiator cap.

It seems like to me something in the system stops working all of a sudden and makes it heat up really fast and then starts working agian and cools it down. but i could easily be wrong.

please help with this.

(Eckks-Jay)

Fan clutch kicking in?

BuckB91XJ

Sounds like your auxilliary electric fan isn't kicking on when it's supposed to.

Abovetimberline

Is your electric fan coming on?next time this happens see if it is,if not turn your a/c on this should start the electric fan,if it does start then your temp switch on the thermostate housing is bad. It is possible also that your thermostate can be sticking.

4.0cherokee

mine is doing the exact same thing and my aux fan is on. I am going to install a fan on the front side that will be a toggle next to me Hella lights on the dash.

Mike1998XJ

What suggestions have you tried since you posted this a few days ago? As I remember many people gave you advice on things to try. It would help us out to know how far you got on those suggestions. Here is the post...
https://www.cherokeeforum.com/f2/running-hot-19535/

warthog

I replaced the thermostat and the radiator cap with a 16psi pressure release cap. The PO said he replaced the water pump radiator and hoses. i will call him tomorrow to confirm that. i reposted bc i had more details because this never happened to me. it happened to a brother in law when they where delivering the jeep to me ( i bought it out of state and family brought it to me ). i have seen the electric fan on but not sure if it comes on on the right time. i just went out to check to see if the fan would move with the engine off and it would.

warthog

i will also order a new temp sensor tomorrow.

warthog

now i dont think its an electrical problem. i actually see it overflowing

I just got off the phone with the PO and he said when he changed the radiator hoses he noticed that one of them was a lot stiffer than the new one. this sounds like this would cause the sudden spike in temperature that i am having. if the hose closes and does not allow coolant to pass then the temp would suddenly rise, right?

also just got off the phone with the jeep dealership ( only wire rigid hose i can find) and he didnt know if it was the upper or lower hose that should be more firm hose.
anyone know


oh if i didnt put it in this thread. here is what is happening.
my normal idle temp would be around 210 then all of a sudden it would spike into the red. i would shut it off, raise the hood and you can hear it boiling into the overflow tank. i have a new pressure release radiator cap. so when i would release the pressure on the cap, the overflow tank would overflow. then i would turn the key on and after a minute or so the guage would come back down to around 215

4.3L XJ

It is the lower hose that needs to be stiff or reinforced with a spring. The idea is that if there is a surge in the coolant, the hose can collapse and cut the flow of water off. The upper hose however is slightly pressurized, so it will not collapse.

Mike1998XJ

To me that sounds like a classic "air-in-the-system" issue. When you filled the coolant did you have the heater on hot and the blower fan on high? Is the radiator fill clean where the cap screws on? If you still have your old cap I'd try and put that back on. That cap you bought has a tab on top where you can pull up on it to release the pressure right? But the stock one didn't... That shouldn't matter but at this point we need to eliminate any variables in the system. Clean the rubber seal on the old cap and try it with that after you make sure the radiator is full.
I know these are supposed to be self burping systems but yours may have a ton of air in it and that funky cap may not be allowing it to work correctly.
Mike

warthog

dang i think i threw the old cap away. didnt think i needed it anymore. i did run it with the cap off and heater blasting and added as much fluid as it will take. not exactly sure how much coolant is in it. i want to do a complete drain and flush hopefully ole mr. haynes can help me out on that. like i said previously. i have no experience when it comes to the coolant system.

Jenkins

This is exactly what my jeep is doing, and I know the electric fan isn't coming on. The coolant sits in the radiator and cools when you shut it off, then when you refire the engine that coolant quickly brings the temp back down.

Mike1998XJ

Ok, well maybe you can find the old cap. How does the coolant look that you've been releasing the blowoff on the cap look? You can view it in the overflow bottle. You could take that off and clean it too. That way after you flush it and put fresh coolant in the overflow you will be able to judge how well the flush worked, because these motors are made to flow coolant into the overflow bottle and then suck it back in. Thus the Full Hot and Full Cold lines on the bottle. Once it does that a few times note the fluid in the bottle to see if it's pretty clean. If it is you did a nice flush... Just my opinion on what I've noticed over the years!
Bye the way when you release the pressure on the cap it is perfectly normal for the coolant (under Pressure) to flow out... That doesn't mean yours isn't overheating, it just means that I wouldn't place too much faith in that. You haynes manual has a section on it on how to check the water pump, you could do that, it's in chapter 3...
Mike

warthog

so i am confused, what exactly are you suggesting? my electric does run but not sure if it is running when it needs to. i am going to replace the lower radiator hose just to rule that out bc the PO said he put a soft one on there.