1965 mustang heater wont work

I have a 1965 mustang with a 98 explorer .302 5.0 motor in it and my heater blows cold air. I have installed a new heater core, New thermostat, and blower motor. The heater hoses are not getting hot at all, even though my temp gauge registers hot when I leave it running for a long time sitting still. I have the hoses going from the inlet of the heater core to the water pump and the outlet of the heater core going to the thermostat (housing?). Can anyone please tell me why in the world the hoses are not getting hot?