[awbrown]

you are not getting any flow through the core , post a picture of how your hoses are routed and where they hook up to the engine .. if you have a new core (brand new not used ) then your problem is else where .. both tubes on the heater core should be hot ,if only one is it has to be a flow problem .. you should not have to "burp" the heater core because flow will start the minute you fire the engine ,the line coming from the water pump will have more than enough pressure to flush out any air in the heater core.. 2 more things to think about , do you have a temp gauge on the vehicle??? are you sure your thermostat is working properly???