I have read for weeks looking for the same scenario. So here goes
Bought my jeep a year and a half ago with 89k, I noticed last winter a small leak from the drain plug and replaced with an OEM radiator, filled, burped, filled overflow to proper line........all WAS well.
This summer I noticed it was starting to get hot driving around town, all was good on the highway (more air flow, I get that), but in town it was getting in the 230 range. I checked the overflow which was bone dry and ended up adding a gallon to get the levels back to normal. Ran good for a few hundred miles then started getting hot again on a 500 mile round trip to KC but only when I stopped for gas or was in slow traffic. I did a little run trial run around town and after getting up to temp I would pull over for a few minutes or putt around in second and the damn thing jumped into the red, 250+, yikes really concerned, but hopefully not too late......
Now home I checked and had to add another gallon to return the levels to normal. My only excuse is that I have not seen any sign of leaks at all and I was convinced that a gallon doesn't just go away in 500 miles, but it did.
So, I had it pressure tested and it lost a few psi over about 20min and the mechanic said it was a head gasket..... , im not a pressure test expert but he put in on and pressurized to 15 then had me start it and move it over to another stall?? Would this give an accurate test?? I don't know, my guess is once it pressurized it should stay that way??
2 gallons in less then 1000 miles and not a drop one under the hood or on the ground, I'm in disbelief. HELP!!!!
I had a very small crack in my rad and never noticed a leak of any kind, but like you I was losing coolant pretty quickly. It wasn't until the crack expanded and I left the engine run with the hood up I was able to see steam escaping. This rad was only two months old mind you. I'd say it's possible you have a small leak that is venting steam and you just don't notice it. Try a new rad it's cheap and quick and maybe your current rad has a lifetime warranty like mind did.
Chances are that if your head gasket is bad, you will have coolant in your oil. Now, it's not always true, but it's the most common thing to happen when a head gasket craps out. Check to see that your oil isn't milky.
Run the vehicle, pop the hood, and see if there's any steam.
Here's some other things to check for:
If you turn on the heater does it cool down any?
The upper radiator hose should be hot, the lower should be cooler, but not cold (if the radiator was plugged, the lower hose would be cold. It would also build up some extra pressure and possibly cause a leak).
When you have it running and you have the rad cap off, looking inside of it -- can you see the water flowing once you reach operating temp?
If it stays cool while driving, then it's also possible the radiator fins are clogged with mud or dirt and air can't flow through. Try washing out the fins from the front and the back and see if it still happens. The leak could be a separate problem, altogether.
Check to see if you have the 0331 cylinder head. I have a 2001 TJ and had that head. Defective from factory. Had a hairline fracture between #3 and #4 cylinder. It would leak coolant into the block more when heated up due to expansion of the crack. All out of warranty mind you. I fought the leak gir about a 2 yrs, changing oil every 1000 miles and adding coolant more often then fuel. Lol. I have since put in a Golen 4.6 stroker. Love it!
You sure can do the head gasket on your own if you'd like. Have a friend help you lift it, though.
Also if you take it off, buy a machined true surface to make sure the head isn't warped. Not that I'm saying it is, but it's always good practice to do.
while running and at running operating temp check the exhaust for liquid coming from tail pipe. could be head gasket or a few other things. getting hot while idling sounds like airflow . check belts for sure. most of the time a head gasket blown will not get water in the oil, but it does happen. more likely to see liquid out the exhaust from blown head gasket.