heater core

[Wiseman]

Hose coming from head goes to inlet side . Inside heater core box there should be electric or manual/cable (depends on what controls you have)valve on inlet side . On others is on the firewall. Either case there should be valve on .
Pressure is different around the jacket . The closer to pump outlet the higher , and vise-versa .
It easy can get well above 60 psi . The higher the rpms the higher the pressure. Don’t confuse this pressure with the system pressure at expansion tank!
This is only basic explanation. There’s more science to it and isn’t simple as it sounds.