Classic/Antique Car Repair: Radiator Cap for 1936 Cadillac, blown head gaskets, radiator hoses

Question
I recently bought a 1936 Cadillac. It is in really good shape but it overheats. I have checked for water pump function, blown head gaskets, collapsing radiator hoses and have flushed the system. The car does not use a conventional thermostat. The radiator cap does not hold pressure (supposed to be 4#)
Do you know of a source for a replacement cap?

Answer
I am  Model a guy.  I don't know anything about your car.  I think the rad is probably plugged.  Most Model a rad's are partially plugged and we fight them all the time.  It is very hard to flow a rad to determine if it is open.  Some people fill the rad, then time how long it takes to let it flow out.  This is a joke and tells you nothing about the rad.  It need to be flowed full and measure the flow rate that way.  The 4# cap will help.  They should be available from antique parts suppliers.  Call Gaslight at 937 652 2145 and talk to them.  If they don't have one, they may know where you might find one.  My Model A sources don't have them.  Find a cadillac car club and join it.  They will be able to help you out a lot.  A loose head gasket can cause overheating.  Make sure the head is torqued down tight.  Also, check the compression.  If you are getting combustion gases in the water jacket from a blown gasket, it should show up with the compression check.  If you can get a shop to rod out the radiator, spend the money to do it.  Back flushing and boiling out does not clear an old rad.  Rod it out.
Good luck.
jack