Airlock??????

Air lock is basically where you have some air stuck within the cooling circulation system mate, it means the car will be holding less coolant than it should be and won't be cooling as well due to air in the pipe rather than coolant.

To remove an airlock you need to bleed the system of air, best way is to park it on a slope with the front higher than the back and run the car with the heater set to hot, remove the cap as you do it, always worked for me but others will suggest different methods probably.