So this got me thinking. I always kinda assumed it was the water flow being reversed but after reading through this thread I realize that did not make sense. After a little speculation it dawned on me that it must actually be how the the belt is driving the pump. A quick search to look at the way the belts turn the pump shows the serpentine set up turns the pump in a counter clockwise and v-belt in a clockwise direction. So with a serpentine set up the internal pump design is flipped to keep coolant flowing in the proper direction.
In your case I would look into an air pocket, heater control valve sticking or clogged core. I would also start by feeling the hoses.

 

Jim karat

You are correct, I did not think about the internals of the though. Yes the fan for lack of a better term, is reversed as well.
So to sum it up, the water must flow in the same direction through the engine despite the rotation direction.
So I suppose all is the same then. I am thinking that it must be an air pocket.

 

so just to double check, the water does, or does not flow through the engine the same?

 

Same way