hi there you havnt said anything about the cylinder head thermostat being changed first thing to change ideally. you say the the rad fans cut in which is half the job there supposed to do but do they cut of after a short while with the engine still running if so theres not much wrong.check the water system has circulation that is water coming back upto the exspansion bottle through the smaller pipe. check that the water hoses arnt getting rock hard this could be head gasket gone over one of the water ways compressing the water system. when the engine is running release any pressure in the exspansion bottle be sensible put an old towel over it first undo the cap a minute or two after there shouldnt be hardly any pressure build up so quick if so this also could point to head gasket