Thanks for the ideas of what to pursue.
The radiator cap came with the NEW Champion radiator that has the overflow on the neck. Seems as if the higher temps are dropping as I drive it more......possibly just now breaking in?
The heater core is part of the Air Conditioning system I installed, so it it modern day; but still 13 psi seems high and I will change for a 4 psi cap. I will test with a heat gun and report the findings.
