1968 Dart cooling system & gauge Questions

68Dart270 said
In fact,as I mentioned earlier,the top hose never seems to be under pressure at all and I can remove the cap even when its at operating temp,which is unusual.

Dana67Dart said
in the Pressure on demand the valve under the cap stays open till there is a rapid flow of gasses out the cap then it closes and the system pressurizes till it is below the set point then is depressurizes

good video on OEM Chrysler cooling systems

As Dana wrote and the MTSC explains, the 'leak' is in the design.
Master Technician Service Conference - Chrysler's Training for Mechanics

With the Chrysler systems at that time, they only become pressurized when there is vapor pressure.

OK, Tech. Set me straight.