Looking for a Stant/MOPAR radiator cap for my 73 Dart

Hmmm just checked on orielly auto parts and they show it as a 16 psi relief pressure not 13

Napa says 16 psi as well.

Advanced auto lists the number you mentioned as 10231
And is rated for 16 psi relief.

Does your old one have a brass cap or plug in the center of it? If so it is vented


Oh all the oe style caps will be vented, this is to relieve pressure in the event of pressure build up to prevent hoses from blowing out etc