So I have read a couple different threads about similar problems but have not found an answer. I drove my 1999 XJ Sport 4.0 about 45 minutes from home. Once I got to my destination and shUT it off, it overheated and dumped a bunch of coolant out of the coolant reservoir overflow hole. I let it cool down for 3 hours and then topped off the coolant and drove it to the nearest auto store. Put a new thermostat in filled it with new coolant and drove it about an hour home. It ran perfect almost the whole way, good temperasure and everything. Then about 5 minutes from home at a stop sign it started idling rough and sounded like a diesel Truck for the rest of the way home. Now it idles rough, runs rough, and shakes the whole jeep when it idles. Really need help on this one and anything is appreciated, thanks in advance!

 

Did it show a high temp overheated at the stop sign?

 

Cracked head

 

Any coolant in the oil or vice-versa? Is it still pushing coolant out of the overflow? If the head is cracked, it is possible for combustion to pressurize the cooling system which would push coolant out of the overflow or even out of the rad cap. Need more details!

 

There isn't any oil on the coolant that I could see. Gotta look into it more after work. Really hoping it's not a cracked head. How could I find out if my head is cracked?

 

Pressure test or block test