My '37 was converted to a pressure radiator when I had the core replaced. I only ran a 4 psi cap and still had problems with it. The brass of the top tank is very thin and every heat cycle it went through you could hear it pop ( expand ). After a year of this the seam would start to leak so I would pull it out and reseal it. I did this about four times before switching to a new aluminum replacement. I never tried it with zero pressure. The new one came with a 21 psi cap !
Joe
