When two of our GE-9E gas turbines were commissioned we observed that time for both GT after a shutdown the ventilation fan for Turbine compartment (88BT) was running for compartment cooling as well as Turbine casing cooling. The fan was stop after certain time period and again start after 15 min and run for 1-hour and again stop. this was continued till the highest wheelspace temperature reduced to 300 degF. But at present we are observing the 88FV fan keep running for long time rather than the previous operations of 88BT. We notified to GE local T/A about the matter, but did not get any satisfactory answer. Can anyone has the correct and authentic answer of running 88BT for the cooling purpose?