This particular model JGC has no electric fan. Ive checked the fan clutch, thoroughly flushed and checked the radiator, changed the tstat and verified that the water pump is circulating coolant. It only overheats on warmer days and if she turns the heater on and blower on high, it seems to help.
Do these models do that air sucking thing if there is some kind of leak in the system?
If not, will burping solve this issue?
Can anyone tell me if this problem can be solved with the addition of an electric fan on the front side of the radiator between the grill and radiator?
***************PLEASE HELP*********************

 

How old is your fan clutch?
How old is your radiator cap?
How old is your waterpump?

Start with radiator cap, if there is something wrong with that then there isnt correct preasure.
The fanclutch need to be replaced if its old. When you start your eninge from cold, the fan should spin fast and you should hear the fan inside the car. After 1-2 km the fan should relax until the engine get hot, then you should hear it again.

 

The 4.0 is notorious for broken water pump impellers, plastics ones, that is. The back of the pump is completely open to the water jacket and the impeller spins only 1/16" from the first cylinder barrel. When the bearing wears, the impeller can move around and strike the barrel and crack or shatter. My 97 ZJ's pump impeller was steel but sounded funny so I took the belt off and I could move the fan up and down about 1/4" but it wasn't leaking. When I took it apart to replace it, there was a bright groove on the cylinder barrel where it was hitting. I replaced it with a NAPA Premium pump which was steel. Also, you have to buy one for the belt system you have because the V-belt ones and the surp ones spin in opposite directions.

They are also notorious for air pockets in the head. The best way to refill and bleed air from the head is to remove the temp sensor from the t-stat housing and fill it until coolant runs out of the hole, reinsert the sensor, and finish filling. I've seen some older ones with a petcock installed in the t-stat housing for this purpose.

Heater on high has always been a way to cool down an overheating engine, regardless of what it is.

I would suspect you're not getting the flow you think you are, or there's air in the head. You might want to look at the radiator core to see if it's plugged with bugs and debris, or needs an internal cleaning.

 

Another god way to remove air is to be sure that the t-stat has the litle bleeding hole in top.

 

That little bleed hole is fine, but it takes a long time to bleed all the air out.