Thanks doc. I doubt anyone would remember to close the valve at the engine on hot/warm days but I don't think it would be an issue, unless you boat in 80 degree water on 100 degree days. But then again, you probably wouldn't have a heater if you did

I don't think I'd pay $40 for it anyway. We only idle for short periods of time and there is plenty of heat from the heater for those short periods.