Radiator Plug Blown out..

Hi All

I changed the head gasket on a 1998 Discovery 1 the other week and tonight the radiator plug blew out and it lost quite abit of water. Any ideas why the plug blew? could it just be that it is old and the pressure was too much? The temperature was ok, when i changed the gasket i found the thremostat was not working so changed that too could this be a problem again?

Cheers

Rob

As the plug is plastic/nylon the thread can wear if it's been in/out a few times so replace it with a brass plug the thread is 1/2 BSP.