heater/defroster question

May be caused by air pocket in heater core. Outlet side heater hose has a small hole provided to bleed air from system at heater core. Loosen and slide hose out far enough to expose hole, then rev engine to about 2500 RPM several times until a steady stream of coolant with no air bubbles sprays vertically from hole, then push hose back into position and top off cooling system. Somewhat cooler output from heater at idle is normal, but not cold.