First of all, and it may sound too obious, NEVER REMOVE THE CAP WHEN HOT !!! And never add water to the radiator with the engine hot ( that will damage the engine, believe it !!!!!
If I`m not wrong, if your system has a leak, the overflow bottle will not serve any purpose if its full because if there is no vacuum due to the leak, the water can not go to the radiator when needed the most, so keep looking until you find the leak because it will cost you $$$$$$ later. Do like the others say, check for a vapor when engine is hot at night with a flashlight, you will see the vapor somewhere. If the smell is not inside the Jeep, dont worry about the Heater Core for now. If you are loosing it, it is going somewhere, look for drips on the floor with the engine running hot, replace the radiator cap ( when cold ) with a known good one and make sure the rubber seal is clean-clean and that the mouth seal ring is perfectly smooth. Check your tail pipe engine running, does it smell funny, yes, run to a mechanic. Check the oil, is it gold or black, ok, is it milky or brown, run to a mechanic. Anywho, don`t stop until you find the leak, you will save tons of money and a bad day from happening. If you can`t find it yet, keep asking....keep looking.