I would like to turn off the flow through the heater core in the summer. Reason? Some heater cores fail from erosion caused by coolant flow. The ball valve with the red handle, which I added when I installed a coolant filter, will enable me to shut off the flow. Heat regulation in the cab is through an air flow door, there is no coolant valve regulating temperature. The 4.3 in my truck has a bypass hose from the stat housing to the water pump. So I think the core isn't needed for bypass purposes.