I purchased a heater from ebay with the round heater core, took it to the local radiator repair shop for testing, the guy at the shop tested and said it had some leakes, he repaired and told me that you don't want to pressure test these old heaters over 7 lbs and that I needed to run a a 7 lb cap or less on my truck. He said that the old heater cores weren't design to handle a lot of pressure and if it was tested with more than 7 lbs of pressure it would weaken the core. I told him that I had a 14 lb cap and he said that the core would probably hold for awhile and then start leaking, so I changed the cap.Still working on restoring the heater so don't know if it will leak on me or not.
