Need everyones opinion on why the radiator is smoking.

Its a fresh motor and i am so paranoid of over heating or blowing a head gasket. I just ordered a new temp gauge since the last one was on the fritz. Without the gauge i feel i shouldnt run the motor too long. What on the motor would be a tell tale sign its over heating. Because obviously the radiator is hot but what on a motor would be a sign its getting too hot? Or maybe i will wait until the new gauge gets in.