Is my Honda's radiator is playing games with me?

[Rad]

Ok. I am not a car expert so I need your help here.. I have a Honda Accord 1990 that has been running very fine for more than 3 years. About 2 weeks ago I realized it had no water in the radiator's bottle, which was unexpected but probably acceptable. I filled it up but the next day the bottle was empty again. I thought this was because I should have also filled up the radiator not only the bottle. So this time I filled both the radiator and the bottle. All seemed fine for about 3 to 4 days but the bottle was almost empty after that, which was way too quick, so I filled it up again. Yesterday I checked the oil and filled up the radiator with water and we drove for about 250km with the temperature indicator sitting in the middle (as it has been for the last 3 years). However today when I drove the car I heard some noise resembling when air is escaping under pressure from a hole or a crack. I checked and the radiator and the bottle were empty and the radiator was totally dry. The noise was coming from the middle of the compartment (about 30cm away from the radiator and very close to the bottom of the engine). I have been checking leeks regularly in the last 2 weeks, and except for once when I saw about the volume of a cup of water lost on the ground the other times I would find nothing or few drops. The car still runs fine and there has been no excess in fuel consumption.. Does anyone know what could the problem be? Thanks so much for your help.