Good to see a lot of support for installing the thermostat valve. Along the lines, my recommendations are to buy a new one, the best Japanese or Genuine that you can get for your car. Old ones from junkyard can never be reliable plus they also have use on them. So opt for the best new one.
The other thing is coolant. My understanding on it is that it also works as anti-rust element. As it circulates in the radiatior and in the parts of the engine, I wouldn't rely on plain water and invite rust in the engine area. So, coolant whether summers or winters. (Caltex Orange coolant is probably the best that I have found locally, so far.)
