My 99 xj keeps over heating. I stop and cut it off and coolant popes out of the overflow tank. Help on figuring out what it is.

 

https://www.cherokeeforum.com/f2/you...system-144771/

 

There are a lot of threads on this, even as we speak.
Try to see if you can find answers in there. do a search.
Otherwise, we will need a bit more info about when what happends (driving or idle, what has been done to it etc etc)
Overheating is a (typical XJ) symptom and needs a systematic approach since the underlying cause can be simple (radiator cap) to complex (e.g. cracked heads etc).
See how you go by doing a search on this and let us know.

 

Had this same exact problem. Check the threads on the cap and the overflow tank. Because they're made out of cheap plastic the plastic expands. Just order a new overflow tank, and you'll be fine. http://www.ebay.com/itm/COOLANT-RESE...item20b26d0a54