1985 Evinrude Relief valve

[stevew]

Hi I have just removed my thermostat, (To find it in many pieces) easy fix. But my question is that I have 2 x relief valves. In the drawings it shows only one. Could you please explain how they work and what is the advantage of having two ?. Also could you please inform me of what temp the new thermostat part No (0382385) should operate ?
Many Thanks
Steve

[boats.net]

Some have two pressure valves, I am uncertain to the reason. There are no notes on the opening of the thermostats most are around 160 degrees.