The other day i was waiting in the arbys drive-thru and she was running a little hot so i was watching it like a hawk. Then out of nowhere it jumped up to 250 and stayed there till i started moving and jumped back down to 220 really quick. Any ideas?

 

I had this happen in the first cherokee I owned when I was like 17 it was an 89 and it ended up being the thermostat was bad.

 

I dont think thats it. The temp gage LEAPED. It didnt just rise. It skipped. Theres no way even if the thermostat was closed that it could have jumped that much then go back in an instant.

 

Have u checked electrical connections at the coolant temp sensor and/or the temp gauge sending unit, if it's a '96 down?

 

Its a 99. Where is it?

 

On/in the t-stat cover.

 

It rises fast because that little section of gauge is a smaller incriment than the first half of the gauge. Im not sure of the exact numbers so just to throw you an idea ill use the numbers 1 to 200. If you split the gauge into two halfs then the first half of the gauge would be like 1 to 150 and the second half is like 150 to 200. Thats why once it starts getting too hot it looks like it jumps up instead of moving slow like first half.

As for it being too hot in the first place thats another problem that these previous comments seem to be your best bet

 

Something like this.......and mathematically, overheat starts at 241.25F

 

Also, the gauge isn't a direct reading off the temp sensor. Temp sensor --->computer--->gauge. IOW, the computer moves the needle where it wants to. If it wants to get your attention, it can quickly move the needle to the right.

You could certainly be right, the problem may be the sensor, but as mentioned, it could also be the 'stat (or something else).

 

Thank you sir! Lol