I have a 2006 Malibu with a 3.5 engine. Trying to change the antifreeze. Drained the old, filled the expansion tank with water for a flush. Ran the motor, but no heat from the heater. Drained the water. Installed the new antifreeze. Still no heat from the heater. If I let the motor run long enough the temp gauge climbs to hot. I know that I probably have an air bubble in the system. Have tried higher RPM still no heat. The engine will get to temp and the fans will kick on, but no heat. Hoses are not getting warm. Everything worked fine before drain and fill. Any Ideas?