When i drive my car in the beggining for about the first 10 minutes my is running the way it should be strong and fast,but it seems to me the longer im driving it the weaker and slower it gets until finally it overheats, i just want to know if radiator is done, its a 90 civic,same radiotor,it doesnt leak coolant i checked,although it does boil like crazy,head gasket is not blown oil is not milky.do u think i should by a new radiator, cause i got the money to do it this friday but not sure?