Would changing from a v-belt to a serpetine belt on an 87 mustang make the water pump run backward?
Depends on how you ran the belt. On a V belt, looking at the
front of the motor, the water pump would be turning clockwise. If
on the serpentine you ran under the water pumppully and are running
on the back side of the belt as some do, then the pump would be
turning counter clockwise and yes, running backwards.