Core Plugs

Mike,  when pressure testing the casting (main block or cylinder head) in isolation, it is not unusual to test for leaks at 60psi as an attempt to identify sources of leaks and to minimise the chances of unexpected core plug failure under real world conditions (i.e. hot combined with fluctuating pressure as the thermostat opens and closes, and localised boiling). I am not saying that 5psi is not enough, but I have seen core plugs that I tested at about 20psi cold, fail and pop out (due to my incompetence!) when everything is put back on the car and the car is used in anger.  PS. testing at such high pressures with the system fully installed on the car may risk of causing other problems in the radiator, the water pump etc..  which you could do without!  Dave Posted by DaveT 06/05/2014 11:35:06

The domed discs are actually  "Welch Plugs"  no connection with Wales. According to Wikipedia they were invented by the Welch bros who ran the Welch Car Co in Pontiac Michigan in the early 1900's .The Hubbard Spring Co of Michigan helped develop these plugs and had exclusivity of manufacture & still make them. There is a fascinating data sheet on how you should fit them depending on size etc.. Posted by Peter Martin 14/05/2014 15:26:02