Overheating-90 Cherokee

[mysticsun]

Hello,

Tonight on my way home my heater started blowing cold air and I looked up and saw my temp guage was past the red line. I pulled over at the gas station and my husband checked the fluids and it was almost empty, so he of course filled it up. Within minutes it had boiled away to nothing!! We drove to my parents house a few miles away and looked at it further. They replaced the theromostat and it's still doing the same thing. As far as they could tell, there wasn't any water leaking from anywhere. It's a Jeep Cherokee Laredo-1990 inline 6 engine. Any suggestions would be greatly appreciated. I've heard from several people tonight about all the different things it could be. Starting with a water pump, head gasket, cracked head, broken or loose radiator hoses, etc. I hope someone will be able to shed some light on this for me.

[Ray H]

ok, your cold heater and overheating engine is because of low coolant or you start out with enough coolant but its not circulating well then it boils down and becomes low.
Worst case is that the head is cracked or head gasket is blown and your coolant is blowing out the exhaust or filling your oil. Is your exhaust steamy even after its warmed up? Is your engine oil frothy or creamy looking or increasing? Unfortunely it sounds like a head or head gasket problem because coolant doesnt just disappear, if its not on the ground, its going somewhere. If you dont have any symptoms from above and its not leaking externally, check for circulation. Maybe pull that t-stat back out and see if the coolant is circulating by feeling the upper hose for heat and movement of the fluid and by looking in the radiator for fluid movement.
Best case is that its not circulating well enough to cool the engine because your lower coolant hose is collapsing shut and its just heating up and boiling off. I would have someone check the lower hose out as its running.
Could be the pump. They will usually leak a little when they go bad though. Look at the front of the engine for a small stream of coolant coming from the pump.
A clogged radiator doesnt come on suddenly like you describe but its another possibility.
I dont know what year the XJ went from a closed cooling system with a pressurized overflow bottle but if its closed, it needs to be "burped" after the system is drained. You can do this by loosening the temp sensor at the rear of the cylinder head while its running, to allow air to escape. Air in the closed system will cause it to over heat and also make it appear full, but its not.

[wwwildman]

Originally Posted by mysticsun

Hello,

Tonight on my way home my heater started blowing cold air and I looked up and saw my temp guage was past the red line. I pulled over at the gas station and my husband checked the fluids and it was almost empty, so he of course filled it up. Within minutes it had boiled away to nothing!! We drove to my parents house a few miles away and looked at it further. They replaced the theromostat and it's still doing the same thing. As far as they could tell, there wasn't any water leaking from anywhere. It's a Jeep Cherokee Laredo-1990 inline 6 engine. Any suggestions would be greatly appreciated. I've heard from several people tonight about all the different things it could be. Starting with a water pump, head gasket, cracked head, broken or loose radiator hoses, etc. I hope someone will be able to shed some light on this for me.

My wife's 87 did the same thing in front of our insurance office and I had to replace the thermostat, but I could not figure out why it keep overheating after the repair until my father-in-law said I need to burp the air out of the system. It is pretty easy to do. This is how I did it:

I filled the overflow bottle with coolant and started the Jeep. I let it idle until it reached operating temp. Then I shut it off and let it cool. I then filled the overflow bottle and repeating the above steps until the motor did not suck anymore coolant from the bottle when it cooled. She has not had a problem with it since.

Hope this helps.