Odd phenomena

[MissahPapaJ]

I’d like to call this a dumb question.. but I’ve sure as hell never seen this. When I open up my radiator cap even after not running for several days ( I walk to work ) it’ll still have slight pressure behind the cap and a little coolant may slightly spill over, dead cold several days.
The entire cooling system is redone except the upper hose water outlet pipe gasket
All OE parts excluding a Land Tank modded blue hub and a rear heater delete.
And the radiator is a CFC ( not in love with that brand but it looked too good ( newish ) not to rock and see if it keeps her cool.
Vehicle never gets past 188-190 after a heat soak and usually runs between 178-181/185 when driving no matter the ambiant temp.

Any thoughts I’ve been wrenching for 20 years and I don’t think I’ve ever popped a rad cap even the next day where it decided there was slightly too much coolant and wanted some out, usually the rad cap and overflow tank swap spit and all is happy.

Side note if this is a CFC radiator inconsistency I’m gonna TYC this hoe so quick.

 

[Irish Reiver]

Just spit balling here with some thoughts. The cap is set to release when pressures in the radiator reach 15psi so in theory once the pressure is, let's say 14psi, the cap will be closed and the cooling system will remain pressurized at 14psi. Obviously, as the temperature of the coolant drops the pressure will also drop but i have no idea how long, if ever for the coolant pressure to drop to 0 psi. So in my mind when you open the cap you release whatever little bit of pressure is remaining. I think you just have a perfectly sealed cooling system.