Hi, can someone tell me why you would want to turn the O/D switch off on the Ford Explorer. The manuel says that it should be on at all times.

 

the overdrive is only to be switched off if the gearbox is hunting for the correct gear for example on a steep hill, it may not be able to decide if 4 or 5 is best and keep swapping- thats about the only reason.
Its is best to let the box to its thing unless you really are suffering!