BMW 3 Series overheating

hi all my bm has started overheating,ive changed the warter pump and the viscouse fan and ive taken the thermostat out,ive bled the system a million times,ive striped the top end of the engin eg the injection system so i could get to the the hoses at the back of the engin to see if there where any blockajes,and there where none,i dont have any milky residue under the oil cap and im not leaking warter,the outher dayb i drove the car for about 45 min and the temp suddenley went to red,i started to pull over and the temp went back down to half way again,so i carried on driving,anouther ten min driving and the temp went up again i checked the engin and the top hose was nearley solid and red hot this happens all the time now if i let the car run for half hr eventuely the top hose will presurise and the temp will go up but sometimes the temp will drop on its own please help!!!