Just driving and adding more fluid till the rad is full everytime you check it.

 

Sounds like the air is in the heater core. You can chase out the air by opening the radiator cap (when cool) putting a no spill funnel in there, fill up the funnel. Start the jeep and then the heat on full. Let it run and periodically check on the funnel, refill as it drains. Once the fluid level stays constant, you should have all the air out; with a glove on, or using a rag, give the upper radiator hose a squeeze and make sure no bubbles rise.

 

Start the jeep and then the heat on full

Turning up the heater control has no effect on the air bleeding process on the ZJ, because ZJs don't have a heater valve. The heater core gets 100% coolant flow at all times.

The air will get naturally flushed out within a few drive cycles anyway; that's how the system is designed to work. All you need to do is check the coolant level for the next few days when the engine's cold and top it up if necessary.

 

With the engine cold and not running, fill up radiator to the top. Fill up coolant reservoir tank to full level. Fire up Jeep, drive until warm. Let it cool, check radiator and fill up coolant reservoir + radiator. Do this a few times, and you should get rid of all the air. Make sure your radiator cap is working correctly. If it's old, get a new one. They cost next to nothing..

I had a pretty stubborn air bubble in the system for a month or so the last time I replaced my water pump, but eventually it did go away. I only heard it when firing up my Jeep when it was cold after sitting for a few hours/ overnight.

 

I had this same problem. It started after I changed some hoses but wouldn't go away. I even tried filling it with the jeep parked on a hill. It just kept gurgling. It ended up being a semi plugged heater core. I back flushed it, some guck came out and the waterfall went away.