First,
I am a member of a nissan/infiniti forum. Most brands have 2 or 3 different independent forums. The particular one is much like this forum. High level of inttelegence and technical knowledge being thrown about..
The nissan infiniti site has the FSM for all makes and models. The Field Service Manual is the BIBLE on the specific vehicle.
You have to download one. they are indespensible. I don't refer to mine enough.
Anyway here are 2 pages showing the thermostat #13 and the water control valve #5 (circled and *)
This page shows the water flow(circled in red). notice the therm can be open and the valve closed .
I assume that the valve is a secondary 'thermostat'. My guess is that it helps with gas mileage as the car wars up.
one last thought.
I found the circut for the elecrtic fan. I was able to 'unplug' the circut sending the temperature and telling it when to turn on.
I was able to have it run 100% of the time. I have a regular route on hwy 80 from Auburn CA to Sacramento Ca. about 35 miles. It drops from 1561ft above sealevel to around 150ft at my home. I can usually get 30mpg plus.
with the fan running 100%, the scangauge temp never got above 195 degrees. It stayed abound 185. I got the worst mpg I have ever gotten on that leg 27mpg.
Needless to say the fan is reconnected to the on/off circut.
So I have to think that the 'water valve' is designed to get the temp higher than the therm for fuel economy reasons.