Once the cooling system has been entirely filled with water, the entire circuit has to be bled. The system will not cool properly if the air hasn't completely been removed from the system! This is true for all the components in the cooling circuit. The simplest way to bleed it is to run the pump for about an hour and thus allow all air bubbles to escape.

Before the cooling system can function perfectly, the cooling circuit has to be bled. This can be accomplished by moving the radiator back and forth, allowing the air to escape to the water bottle.

The majority of the air collects in the radiator, which can only work properly if there is no more air trapped in its cooling fins.