2006 Ford E450 Transmission issue

The fan noise you hear is normal and will occur whenever the engine/coolant gets too hot. Either an electric fan comes on, (if equipped) or the (mechanical) radiator fan clutch engages which is the whirring you are hearing. (due to high exterior temperatures, high coolant temperature, towing, uphill grades, etc.) When the engine/coolant gets too hot, the ECU (Engine Control Unit) goes into limp mode and reduces engine power so that you minimize the chances of damaging your engine/transmission. Your Ford Factory Owners Manual clearly explains this. :-) Reducing your speed, turning off your AC, and running in lower gears (higher RPM) if possible, will help minimize this condition if/when it occurs. Make sure your coolant expansion tank is full of fresh correct 50/50% water/coolant mix. If/when you hear the fan clutch engage, if you look at your coolant temperature gauge it should read slightly elevated from normal and should return to normal when the whirring sound stops.

Chum lee