Engine Cooling problem
2000 Nissan Pulsar 4 cyl Front Wheel Drive Manual 120000 miles

My heater stopped working.
I checked my engine cooling system.
Found lots of rusty coloured build up under the radiator cap.
Flushed out the system, added coolant.
Now have an overheating problem and still no heater. I have been told there is a possible air lock inside the engine.
How do I release the air? I have used the valve at the side of the engine, There does not seem to be a 'bubbling' problem.