Which direction does the coolant flow into the heater core? Which hose is the inlet side. Is it from the water pump? I want to install a water control valve to stop the hot water before it enters the heater.

 

Let's think about this for a moment: What pushes the coolant? Yup, the water pump. So the inlet is off the water pump and the valve placement is between it and the heater core. Typically, the valve is opened / closed by the 'Temp' **** on heater controls. The valves certainly can be adjusted manually under the hood as well.

I didn't think it got cold enough in Riverside, CA to need a heater.

 

Well its going to get down into the 90's today! Brrrrrr! Gotta shut off that hot water from running into the cab!

 

Suck it up, cupcake.

 

Technically, it doesn't matter, since heater cores are generally non directional. Just put the shut off valve on the side coming from the water pump, and you're good to go.