ytownxj

So everyone's had overheating problems before it seems like, but in my days of searching I haven't found anyone with one quite like mine. So everything in my cooling system has been replaced, checked, re-replaced except the overflow bottle and the hose that goes from the radiator to it. My temps are fine on the highway and most of the time, but if i'm sitting or driving very slowly for prolonged periods of time it'll sit at 220 (which seems fine to me) but then will jump to 260 in about half a second's time and beep at me. My only theory left I can think of is it must be pulling air in from somewhere and getting trapped in the block letting it heat up real fast. Can this be caused by the things I haven't replaced? Can't find any sign of leaks elsewhere. Any help would be greatly appreciated.

And for the record, I have a flush kit installed with one of the screw off caps at the top, after overheating I can loosen this plastic cap and air will leak out for a good thirty seconds easy before there isn't any left. The overflow bottle will also fill up way past the full mark when it has just overheated to about 5/6ths the way full as well.

thakmfb

Head gasket?. Thats what it sounds like to me. Just because coolant and oil arent mixing doesnt mean your head gasket isnt leaking it could be leaking into a cylinder and burning off or being pushed out the exhaust.

cdf43

just taking a stab but there could be air pockets traped in the system. if you do a flush and dont draw the system into a vacuum its easy to get air pockets traped in the block

ytownxj

Hope not, remanufactured engine put in last September

ytownxj

And cdf43, don't the 98 xj's self bleed? It has an open cooling system

cdf43

from my experiance all cooling systems can get air pockets even with bleeders.

but of course im not an expert hence me just putting in my two cents

cdf43

there is a kit available that detects combustion gasses in the cooling system to see if your head gasket is blow....its a pretty awesome tool

thakmfb

Open/Closed they all can get air pockets. start with making sure all of the air has been bled from the coolant

AlbuquerqueJeepGal

Hi There, I am brand new to this site. I am hoping to get some help in diagnosing a cooling issue. I noticed your thread and have had the same issue that you are currently having. I see that you have replaced many parts to your cooling system and wondered if you had encountered my more pressing current issue, which then progresses to your current issue.... okay...clarification..currently, my 1998 Jeep Cherokee overheats when i am sitting in traffic with the AC on or off. What i have figured out so far, is that when my car is cold and i first start it up, the electric aux. fan is running when i turn on the AC, but after a few minutes, it stops running. Basically, what happens is that when the car warms up and the aux fan should be on, it is not, regardless of whether i am running the AC or not. Obviously, the fan and the motor work. So, I have now replaced the AC clutch relay, as well as the cooling fan relay and the coolant temp switch but the problem still exists. Tying into your issue...while driving on a 4 wheel drive road in Colorado, my car was warming up as expected since the aux fan is not working, and the temp was up to 220 and all of a sudden it shot up to 260. What is up with that?! Sent me into a panic. My question is this..did you have a similar issue with your aux fan and any guesses on how these problems could be related?

freegdr

when the temp rises does the aux fan come on

ytownxj

I've had aux fan problems in the past, got tired of trying to get them working how they should so I just wired the fan to a switch. Keep it on whenever I've got the AC or hot weather and slow speeds, really don't think it does all that much anyways since I have the same problems with it on or off. So I ruled that out as a reason with my problems.

freegdr

when your fan cuts off does the ac stay engaged

ytownxj

To freegdr read my last post. Couldn't figure out how to quote multiple people.

I've bled it many many times using the upper heater hose where I have my flush kit cap. Highest point in the system and I've had air running out of it many many times. There is no way it is making all that air, it has to come from somewhere. Haven't added/changed coolant in about three weeks and bled it tons of times.

cdf43

id empty all the coolant, draw it into a vacuum and put fresh coolant in there....use an air lift tool

bigvig

If you get an air pocket in your system its the FASTEST way to burn a hole in your head gasket too. If your system isnt burped correctly, you can do some major damage to the motor.