I have to wonder. It hasn't been cold as of late (most of my driving it has been during about 80 degree days), and no matter how far or fast I've run the Jeep it hasn't got over something like 140 degrees, so the cooling system doesn't seem 'bad' from what I've seen.
Thus far the things I've found are that the heater core isn't hooked up to the hoses, and the thermostat was taken out of it - perhaps all to just give the riders that much cooler of a ride (less ambient heat from the motor, back, or from the heater core having hot coolant in it).
But, yeah, that would make the most sense - if the YJ had a heating problem.
One thing to always take into consideration is that it was a vehicle from Miami-Dade, and the people down there aren't the most educated lot to be found. They could have taken it out using reasoning none of us would understand, and that science wouldn't support.
But, back to the things that it does do - the already very old hoses are now under more stress since they're beign asked to run at normal temps again. I changed out the upper radiator hose yesterday due to this, and will get to the rest eventually.
Swap out all the coolant hoses...antifreeze/coolant is not cheap and pets will drink the stuff and die...not good.
The heater core could have a leak in it BUT maybe the PO didn't want any ambient heat form the heater core.
One way to find out. Hook it back up and top off the coolant. Rune it until it is hot then check the floorboard on the passenger side of the YJ. See water? Bad heater core.
Make sure the drain for the cabin air inlet in front of the windshield is not clogged up with pine needles etc.
That engine was designed to run at 180F a 195F thermostat accomplishes that. This engine runs it's best ( and cheapest) at that temperature. If it overheats the block water jackets might be be plugged up. But think of that last.
More than likely the radiator is plugged up some.
Radiator check; run it up to temperature then shut it off. Now CAREFULLY
feel the radiator core starting at the center which should be hot. Now check the four corners of the radiator. Are they much cooler? Radiator is plugged up.
IF you live in an area that gets real hot (+100F) for days on end you might want to get a duel or even a triple core radiator.
Another issues is the clutch fan.
On a cold engine the fan should spin fairly free. After the engine is running for a while and it gets up to full temperature it should now be much stiffer.
If it isn't then the clutch mechanism should be replaced. Many YJ'ers opt for an electrical fan of some sort.