Cracked.head
Check the engine thermostat.
If the pump is not circulating coolant insure that the thermostat is not stuck closed. If the thermostat is ok then the pump will have to be replaced.
brilliant, the thermostat is backwards
Perhaps plugged radiator - have it boiled out or replaced
Could be your electric fan on the radiator is shot, or the relay is bad.
YES
Do the electric cooling fans kick on?
have you checked the fan
You might as well change the Thermostat because it is comparatively inexpensive, but test the water pump to see if it needs to be replaced.
Could be a bad water pump.
Could be thermostat not opening causing a back pressure
That is the water pump weep hole. You either misinstalled the gasket, or the new pump is bad.