Am I crazy or what? I know most cars have just one thermostats, but on the 5th gen 3.0 VQ has TWO!? I know one in front of the engine where between the pulleys have a one piece thermostat/housing. As i was replacing the all the hoses, I found another on the back of the engine, you have a water outlet, there's another thermostat. None of the part stores will carry it, so you have to go to Nissan to get it, they call it a Water Outlet Valve which is unusual despite it is a thermostat.

 

Heat control valve

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yep, it's a peculiarity of the VQ in the 00-01 max and also the pathfinder.

 

I'm in the process of switching mine out, should I replace this one too ?

 

I would leave it alone. Not very many people know about it, even fewer have ever changed one. And it never made a bit of difference one way or the other.

 

I would replace both the same time, save your time and trouble if the water valve assembly get stuck closed, then you end up thinking the other thermostat is the culprit.

 

No...leave it alone for the reasons Dennis states. It isn't a good practice to throw parts at a car when troubleshooting.