I run all of mine wide open. No thermostats. If you have O/T headers, you'll probably want to run a separate valve to control the water flow into the headers. I haven't had good luck with the Bassett or Rewarder spring valves working right, but other than that, no other valves are necessary on the system.
The valve you have is a rudementary way to increase water temps in the engine, but a better way is off the exit side, not the inlet side, if this is an issue. Or Both.
One of my boats, Moo, with O/T headers, runs 140-160 all day, any day with the valves wide open. The Pickle doesn't seem to get above 120 with no valves on it at all (Logs and O/T pipes).
Ray