For some reason I was unable to answer your question, but I had this same problem a while ago. The top of the rad is made of brass and it can develop hairline cracks that you are unable to see unless you use dye penetrant.As the engine heats up the cracks open enough to let steam escape (you cannot see it) and all your fluid mysteriously evaporates.
I was puzzled for weeks with it until I finally took my car to a rad specialist. (after I had changed the thermostat and other things)
He knew (suspected) the cause immediately. It cost me a new rad ( not too expensive but cheaper that a new engine!)
Good luck, I hope you get it fixed easily BUT take it to a radiator specialist, not a Mazda dealer or your friendly garage as the will not have a clue, as all the other answers seem to demonstrate.
You can email me.
I was puzzled for weeks with it until I finally took my car to a rad specialist. (after I had changed the thermostat and other things)
He knew (suspected) the cause immediately. It cost me a new rad ( not too expensive but cheaper that a new engine!)
Good luck, I hope you get it fixed easily BUT take it to a radiator specialist, not a Mazda dealer or your friendly garage as the will not have a clue, as all the other answers seem to demonstrate.
You can email me.