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About that thermostat. In all probability, it will not open at all at idle speeds, especially in cold lake water. Under such conditions, the water returns to the water pump for recycling till it gets warm enough to open the thermostat. However, there will be a bit of water bypassing the thermostat even when closed in order to cool the exhaust. That bypass water should show up as a light spray out the exhaust relief port, and when the ‘stat opens the spray will be heavier. Important thing to remember is the ‘stat is constantly sampling the water temperature and opens and/or closes as needed to try to maintain ideal powerhead temperature. In other words, the discharge spray also comes and goes according to thermostat state.