Air Pockets in the Cooling System
Sometimes an air pocket will form after removing a part or flushing the engine's cooling system. This is a problem with certain models, and a special procedure like raising the rear or front of the vehicle is required to remove these difficult pockets.
This question mentions the lower radiator hose. This is a clear indication that the system has drained and now has an air pocket. This can leave the water pump with no coolant to circulate; water pump cavitation.
Note that there are two types of cooling systems, the series and the parallel. A series system flows around the cylinders, then to the back of the block before flowing to the cylinder heads. With a parallel system, the coolant flows around all the cylinders, and through passages located beside each cylinder, then into the cylinder head, instead of sending it to the back of the engine block first.
A special tool can be used to force the coolant into difficult systems using shop air. Remember to use caution when dealing with hot coolant, many have received burns attempting to remove stubborn air pockets.
Check the manufacturer's manual for any special procedures before proceeding. A stubborn air pocket can prevent engine cooling fan operation. If there’s no coolant passing through a closed thermostat and across the (ECT) engine coolant temperature sensor, the PCM will not receive the correct signal preventing vital fan operation.