94 HondaCivic Overheating?

Symptoms: Car overheating when running 15-20 min idle no hot air blowing..Lower hose is cold while upper and radiator is very hot..I have replaced so far Thermostat (correct way installed), radiator, thermo sensor, and water pump was installed 2 years ago shows no sign of leakage or noise..took off hoses and flushed them to get rid of any clogs..also I have bled the system for at least an hour various ways to get any air out of the system and the car is still over heating..have also checked for any white smoke and milky signs in oil and antifreeze everything looks normal...Please if any other suggestion i would greatly appreciate...