Are you saying then engine is running cold or just the interior heat is not warm?
Almost always when an engine runs cold it is a thermostat problem. But if you think the issue is the heater core, loop the heater hose to bypass the heater core and see if the engine runs warmer.
Almost always when an engine runs cold it is a thermostat problem. But if you think the issue is the heater core, loop the heater hose to bypass the heater core and see if the engine runs warmer.
