I have/had a round chrome covered p.o.s radiator cap. Some company was so proud of this piece they did not mark the pressure rating on it. I tore it apart to se if it was marked on the underside. Nothing, I am told I need 15LBS so my car will not overheat. This was not a performance part. It was a Transdapt/Mr. Gasket dress up type of part. Is there a standard pressure rating or what pressure do you think this was? Thanks for listening to my ramble. Brian

Find somebody with a pressure tester that is used to test cooling systems.

There is an adapter for testing caps.

You'll know for sure what it will hold regardless of markings.

note that a higher pressure cap won't make your car stop overheating. It just increases the boiling point of the coolant so it won't boil over until a higher temp.

Pretty sure our stock radiators were designed for 7 psi. New ones will take 15.

Go to your local Radiator shop......they will have a pressure tester.

my 69 is meant to have a 15lb...as these are far and few over here, ands a 13 can be had off the shelf, I use that instead.

Great advice,
I distroyed the cap but I guess it was a 7lb. Now I have a 13lb. I am installing dual 11'' becool/spall fans. I will put the 15 then and see what happines. Thanks everyone. Brian.