It could be that the radiator cap is not able to maintain pressure. Check the radiator cap for cracks or any other damage. Replace if necessary. DO NOT remove the radiator cap when the engine is hot.
the cap is on the coolant surge tank, on side by fender.
A surge tank is basically a pressurized coolant reservoir. As your engine heats and cools the coolant expands and contracts. Because of this You need a place for extra coolant to go to when it expands and be drawn from when it contracts. Conventionally the recovery tank or reservoir was not pressurized. A tube from the radiator cap allowed coolant to be sucked and drained in to the reservoir. However, on many newer vehicles like yours the reservoir is pressurized and called a surge tank.
It is possible for a 1989 Jeep to leak coolant from the surge tank if the vehicle is overheating. It is also possible that the surge tank has a crack in it.
The surge tank is located on the passenger's side of the engine compartment. There is probably a sticker that reads "Use DexaCool Coolant Only."
It is in the bottom of the coolant surge Tank. That is beside the air filter box.
The coolant pump draws coolant from the radiator and circulates the coolant through coolant jackets in the engine cylinder block and the cylinder heads. The coolant is then directed back to the radiator. The system directs some coolant through hoses to the heater core in order to provide for defrost and passenger compartment heat. A surge tank connects to the cooling system. Pressurized coolant continuously flows through the surge tank and the process repeats
trottle control module
a vacuum leak.
The coolant is being circulated by water pump. That is normal operation. Ensure coolant is at proper level (and bled if required).
check coolant level
Rotors are out of round,need to have them turned.
The most common cause of that is a bad EGR Valve.