D65ex-15 hyd overheating

Hi, I have a complicated problem, My D65ex-15Eo 8000 hrs is overheating in the hyds. It is getting pressure at the fan motor if we isolate the pilot lines feed at the pressure reducing valve.The fan has pressure when cold but drops off as the oil heats up. There must be a major bypass of oil somewhere to be creating massive amounts of heat as the oil is going upwards of 90 degrees at half RPM. Any ideas? thanks in advance

D65ex-15 hyd overheating