Yes, water is the best cooling system coolant but need the anti freeze for obvious reasons. As to the thermostat sticking, this should never occur. As to the pump working harder with it open, the pump is running all of the time, never off so it makes no difference on pump longevity. Get the thermostat replaced and sticking should never occur with a clean system and coolant.
I tried Water Wetter also, no noticeable diff .
