Mike - that sounds like a good plan at first, but I'm wondering . . if you tap into the closed loop of the engine when the thermostat is closed, you would then be depleting the water in that loop and only replacing it after the t-stat opened back up. Am I thinking right? I realize that most of us run the boats in warm weather when the t-stat is almost never closed, but it does happen. If you tap in on the "back side", outside of the loop then it wouldn't matter to the engine if the t-stat was opened or closed. I think.