Want to install heater water control valve

Living out here in Arizona I've never used the heater yet. But like you say there must be coolant flowing through the core all the time. I've thought about installing a regular hot water valve from Home Depot in some location where it is not obvious and using that to shut off the water. Not high tech but hey it would work.

An alternative might be to rip out the whole heating system. I can't see me using it out here and I'll save some weight.

Are you getting excessive heat through the vents in the summer? If not, don't worry about it.

There is a flap door in your heater core housing assembly that should shut off all hot air flow. If that doesn't seal, you will get heat leaking through.

Most cars that have this valve are AC cars, and they do it because the AC ducting is shared with the heat ducting. It is far more efficient to cool air that is flowing through a cold heater core than a warm one. The valve is usually vacuum operated and simple in design.

Unless you are getting heat when you don't want it and all your doors are working correctly, I wouldn't worry about it.

All parts houses sell in-line heater hose shut off valves, go get a couple and install them. IMHO,, it's best to use two of them, just incase your heater core decides to spring a leak. If it does, you can shut off the water from both sources.