If you look inside the gash, you will see a thick, rounded growth circling the wound. That is how trees heal over dead areas. It also tells me that the wound is at least three years old, but probably more.
The bark that is peeling off now was dead before, but remained in place so that the wound was not detected right away. I have seen this kind of dead patch after a borer infestation, so you may want to have your tree examined by a professional arborist. But whatever caused it, it still needs to be cleaned up.
Trim off all the dead bark from around the wound. Also, cut away the corky growths along the side and bottom of the wound, being sure to stay clear of the cambium layer (the green layer under the bark). Those corky areas are what is holding in water, and causing the area to stay wet longer.
Do not wrap the wound, because that would cut the air supply and allow no water evaporation, welcoming in the rot.
Your tree is pretty far along in the healing process, and it should heal over completely in the next two-four years or so.
Again, if you want an expert diagnosis on the original cause, and possibly a way to prevent future attacks, you will need to have a professional look at it.