98 xj 209k 4.0, notice today after I let it sit for about 10min running the coolant reservoir started to bubble pretty good and started puking out antifreeze!!! So I cut off the motor to let it cool down and it eventually quit!!! Blown head gasket?? Bad thermostat?? Bad cap??? Idk just got it today!!!

 

When people ask this question I always say start with the radiator cap.
Comes from me being out and about one day in my '00 a few years back.
Stopped to get gas and all of a sudden noticed anti-freeze on the ground under the Jeep.
Popped the hood and it was bubbling out of the overflow tank.
Said to myself well that's new. LOL.
Anyway new cap and was good to go.

 

Yep. Could be any of those things. But, like Ralph said, a cap is easy and cheap. Start there. If that doesn't help, it's time to test for exhaust gasses in the coolant.

 

And PLEASE check all fluid levels and condition before driving it around.

 

Ended up being the cap but I did a flush anyways!!! Shewwww scared me!!! No on to the steering got a lot of play in the steering wheel. It’s got a small lift with 32s!!

 

Good news that it was just the cap. On the steering, crawl underneath while someone turns the steering back-n-forth. Look at and feel everything for play. Track bar is a common problem, then tie rod ends.