its auto. all m35s are auto - not the new PM35s however, but i dont think one has even sold yet!
probably thermostat if its pushing out all the coolant into the overflow bottle and boiling it. or you have an air pocket/blockage. as mentioned above, get it looked it. worst case, get a new thermostat from nissan, or a nismo one.
there is nothing wrong with the standard radiator, only a handfull of people have had problems with the factory ones. mostly cracking or blowing hoses.