Hey guys my 528i is overheating. Upper hose will be hot but lower hose is barely even warm. The temperature will rise into hot, but when i rev the engine more it goes back into normal operating mode. I constantly have to rev it at every traffic light to keep it from over heating. I replaced the thermostat today, still upper hose has pressure after revving it but lower hose does not. What could it be? Any help would be nice since this is my daily driver car. Thanks!