Car does not overheat and heater works great. Not driven in winter not a daily driver. I do have to use the heat sometimes in spring and fall to keep the windows defogged.

What I want to do is install a shutoff valve somewhere in 1 of the 2 heater core (HC) hoses.

When it's hot out I feel like the passenger comparment is getting heat from the HC even though the heat is off.
I'm guessing it's because these cars have a blend door and not a shutoff valve.

If I install a shutoff valve, any ill effects of no coolant flow to the water pump from the HC?

Any one done this?
Any recommendation for a vallve?
Would it matter if the valve is on the inlet or output side of the HC?

 

The cooling system is designed to flow coolant through the heater core at all times. The amount of flow is limited by a flow orifice in one of the lines. If you feel heat coming out when you don't want it, it would indicate the flapper door that controls the selection of hot or cold air is not working properly. That door is operated by a cable from the temperature **** on the HVAC controls.

Check the cable and make sure it's working correctly. If it's working right, you will not feel any hot air from the heater core when you don't want it. Shoebox has a diagram of the system:

http://shbox.com/1/hvac_vacuum.jpg

 

I've thought about doing this for a while, my `80 doesn't have A/C and in the summer it cooks. I work on heavy equipment and there are several machines with gate valves on the heater core lines at the engine it helps with A/C performance.

I was thinking about a H-block with a gate valve that would make a loop from the water pump back to the pump, I'm sure I'd over engineer it.

But, I haven't done it, when I last replaced the heater core I know I don't want to do it again so I'm hesistiant to cut off coolant flow to the core, I don't want corrosion to kill the core from lack of flow or give the system a chance to make air pockets.

Anyway the core also is a portion of the engine cooling system and if you have an engine that runs hot, taking the core out of the loop may increase overall coolant temps.