The reservoir is filling up and will overflow after driving it for about 30 minutes
Do the Glove test to take blown head gasket off the table
remove rad cap
remove overflow hose and plug that port with vacuum cap or ??
Drain some coolant out so it is down about 1", lower is fine.
Put latex glove over rad cap opening and seal it with rubber band, you can use a balloon or even a condom instead of a glove.
If glove inflates then you have a cylinder leaking pressure into cooling system.
A cold engine has no pressure in cooling system, the pressure comes from the coolant heating up and expanding, which takes about 5 to 8 minutes of engine running.
A water "pump" is not really a pump, it is a circulator, like a ceiling fan in your house, it doesn't create high pressure in your house, it just circulates the air.
If glove inflates shut off engine
Pull off spark plug wires
Crank engine and glove should bounce
remove 1 spark plug at a time and crank engine
When glove stops bouncing then last spark plug removed was from leaking cylinder, put it back in to confirm.
This can be helpful when looking for leak point after disassembly