Pete,
I put one of those valves on mine but I haven't driven it in summer yet. It will stop the flow through the heater and cut down on the amount of heat it produces. Some say blocking the flow completely is a bad thing for the core. It really doesn't matter which side the valve goes on as it still stops the flow.
Back east here, it was a day of shoveling yesterday! Driving my truck is still yet just a dream this year!
