cooling problem?

Alright, I have a 89' jeep cherokee with a 94 engine that was switched into it, it has a close cooling system, newer waterpump, a few months ago it overheated on me, i think due to the fact the bottle is cracked and leaked out a lot of the coolant and then it got worse and worse from there, so i shut it off, added coolant before it got up to 260 degrees, and it stayed normal, i thought what the heck might as well replace the thermostat in case it was sticking, so I bought a new 195 degree thermostat, put it in, now since I put it in, at first I thought maybe it was a air bubble, but now it has been over a month of daily driving and it still does it, the very first time you drive it if it is warm or you drive it hard it heats up to problably 210-215ish on the gauge, then drops back down to 150, and after that it slowly builds up to 190ish and then as soon as it gets close to that it drops down very rapidly to 150, it never did it before I replaced the thermostat, and I hate how it warms up past 210, today I didn't pay attention and was really pushing the jeep to see what it would do when i drove it when it was cold, it heated up to 230 ( It was getting close to 5,000 rpms, and this is the first time and only time I ever do it just screwing around) and then it dropped back down to 150, and then didn't heat past 210 after that...so what the heck could cause this?...do you think there is a problem? or is this normal, it never did it before the thermostat, and my moms 00 doesn't do it after I changed her tstat and water pump.

So have you replace the bottle?

That was my thought too. If the bottle isn't holding pressure, you're going to be boiling over pretty easy.

The procedure for the closed system.....ya gotta burp the system...plus the pressure bottles have plastic caps with a rubber Oring on the inside.IMOHO.....the closed system sux....coolant gets low...air gets in the system.....air gets in the system....it overheats......put up with this BS for bout 1 yr...Swapped out to the open system....BINGO.....very minamal overheating.....rad was leaking on a seam.....Rad was and always be LTW..so that was an easy fix...
I personally try to do an cooling system flush every year...change t stat anti freeze..check hoses belts etc.Got this from living in Michigan 22 yrs...trust me you DO NOT want boilovers or cooling system breakdowns in the winter...
Converting from CLOSED to OPEN is a direct swap...cept ya get a radiator cap as a bonus...

I haven't replaced the bottle yet, I am going to soon, I just am wondering why the heck my temp is a constant cycle of going up and down...its really weird....the only time it overheated was the one time when i let the coolant get too low, other than that it never really does it besides yesterday when i really pushed it, and I don't think it was quite to 230 yet....someone told me that all these symptoms sound like a headgasket...would a bad headgasket do this?....the temp cycle i mean?...i have no coolant in the oil, dipstick doesn't look milky, none on the oil cap, and no oil in the coolant, the exhuast doesn't appear to smell sweet or anything and smoke...so i doubted it was the head gasket...but hey you never know...just wondering...thanks!

jeepxj2007 said:

I haven't replaced the bottle yet, I am going to soon, I just am wondering why the heck my temp is a constant cycle of going up and down...its really weird....the only time it overheated was the one time when i let the coolant get too low, other than that it never really does it besides yesterday when i really pushed it, and I don't think it was quite to 230 yet....someone told me that all these symptoms sound like a headgasket...would a bad headgasket do this?....the temp cycle i mean?...i have no coolant in the oil, dipstick doesn't look milky, none on the oil cap, and no oil in the coolant, the exhuast doesn't appear to smell sweet or anything and smoke...so i doubted it was the head gasket...but hey you never know...just wondering...thanks!

Click to expand...

Do you have the 89 or the 94 ECU controls?

Replace the bottle and cap for sure, that will definately cause the symptoms you described. Pressure builds up, then leaks, pressure drops, pressure slowly rebuilds, then leaks again. The cycling pressure will cause the temperature to cycle too!

Mike McGinness
South Houston, TX