I have a 99 Cherokee Sport that overheated yesterday. I as sitting at idle for about 10 minutes with the AC on and the heat was maintaining at about 218 - 220 (when driving it is usually below 210). I decided to turn the AC off and as soon as i did, the temp gauge instantly laid over to about 250 and my check gauges light came on. I pulled over to a park and turned the vehicle off, noticing the sound of bubbling coolant in the radiator. I gave it a few and opened the hood. The overflow tank was way above the full line. I let it cool off for about 20 minutes and the coolant in the overflow tank went back to normal level. I then restarted and immediately my temp started going back down to below 210. i have driven it for about 60 miles since then with everything fine.


Thermostat? Electric Fan? I have never seen a temp gauge instantly jump when the AC is turned off...

also wondering if the electric fan is supposed to kick on when i turn the ac on, regardless of the temp?

 

The electric fan will come on with the A/C. It will also switch on when the temp reaches 218 degrees. If things are fine now, keep a sharp eye on the system for a while. If it happens again you may want to look at your mechanical fan clutch, and maybe replace your radiator cap.

 

"also wondering if the electric fan is supposed to kick on when i turn the ac on, regardless of the temp?" Yes, I believe it does.
Bubbling in the radiator and coolant forced into overflow tank sounds like a sticking thermostat to me... but did it get hot enough to blow a gasket? A blown head gasket in the right place could over pressure the cooling system. Check oil for coolant and coolant for oil maybe?

 

I will try turning the ac on this afternoon to see if the fan kicks in.

 

So....when the electric fan is off, should the blade just spin easily if i try and turn...it seems like it turns some, then hangs up.

 

Yes, you should be able to spin it freely when the fan is off.

 

If you replace the thermostat be sure and insist that you want one with the fail safe mode. They will stay open no matter what causes them to fail, very cheap insurance for only a couple of bucks more.

 

So it wobbles to. Bearing bad I guess. We tried it earlier, leaving the ac on. When the fan was supposed to kick in the volts dropped on my dash and the fan started smoking and smelling burnt.

 

You can test the e-fan for operation by unplugging the connector at the thermostat and starting the engine. Fan should come on.

The magnets in the e-fan motor may cause the kind of jerky stop you are describing when spinning by hand.

Edit: Glad you found it.

 

With regard to a "fail safe" stat (a gimmick, imho), what guarantees it will open? The situation or other component failure that caused the stat to "fail open" needs to be diagnosed/rectified. Other problems arise when a stat remains stuck open.

 

Yep, fan was definitely bad. Replaced it myself for 100 bucks. Fan now kicks on when AC comes on.