I have a 2005 magnum, 3.5 v6 and I want to put a heater core shutoff valve in the water line going in threw the firewall to the heater core. seems like a simple operation EXCEPT there is a "t" in one of the lines and that line goes to the over flow tank, the other end goes back into the engine it looks to me that if I put in a shutoff valve I would also be shutting off the flow to the tank