Coolant Flush, Do I replace the water control valve?

I would change the water control valve as it is the true stat in that engine, the low one really has nothing to do with the cooling of engine.

I for one change stats on every car I have at around 100K + miles, they can commonly go bad and one will never seem to except in the worst possible location to do it. To say if it's not broke don't fix it is begging to melt the engine to a lump, most cars I ever ran the stat too long on tried to burn the engine and where I learned the lesson.

It is rock stupid to wait until the engine overheats to change a stat and why now I haven't been stranded in more than 30 years using any one of 4 old cars, the belts, hoses, and stats get changed at higher mileage before they can ever be an issue. In modern engines one solid overheat can crack the head and fine idea waiting on a $7 stat to do that.

At some point I will likely gut the lower stat to simply use the outer ring as a metering restriction, the lower stat opens before the water control one does and doesn't even need to close as the water control one stops all radiator flow when it closes. Nissan had their heads somewhere else when they came up with that setup, the second stat can only cause added trouble.

I change all hoses and stat at about 100K miles. never change radiator at all, they typically don't break but rarely. Same thing with modern serp belt driven water pumps, I change those maybe 200K miles. The stat and hoses are the most likely thing to fail. If one pays attention the rad, the cap and water pump often give you warning when they are getting old. I simply rebuild the caps to use them over, haven't bought one in 40 years.

All water temp idiot lights go on about 265 degrees F as an industry norm, the problem with todays' thin wall engine castings is that in no way may that be a safe temperature, MANY engines have already warped or cracked a head or block by then. In short, the light comes on too late.

Who cares if Nissan has given a TSB on the water control valve? It is upon people doing the work to understand that those things that should happen often never do and to beyond that grasp how the cars work.

Take most Nissan airbags they were so freaking about just a little while back. They spent millions trying to get everyone to get the 'bad' airbags changed out yet what have they replaced them with??? How about more of the EXACT SAME BAGS that then proceed to age again to go bad in the future. They have mortgaged your life betting you will not have the cars that long. Why I view a question on a TSB as being farcicle. We are talking about the people who gave us CVT after all.

Not about you or me. I apologize for anything you did not like there. It's just that I have a world of experience on things you may not.

I sold parts, so I know what breaks commonly. Take the radiators, they typically break the plastic tanks because somebody at some point overpressured them when a stat that should have been changed did not get it. Or they went until a hose blew out and the same thing. Stop the other parts breaking and suddenly the rads quit too.

I also did garage work and have a better handle than most on doing things out of the box to not pay the big charges so many now have to to get anything done. Just did clockspring on my Versa and price was cost of the part and I modded it as well to do some things in the stack I wanted done. Saved the old clockspring to rework it further to reuse it at some point in the future. Already worked out the repair to cost me maybe $10. I also already have water temp gauge and parts, just haven't installed them yet. I will as well install LEDs on the low and high fans and a/c clutch to be able to see other things like I did on my Fords. The engines now are largely unbreakable if you remove the possibility of an engine overheat ever happening, even one can turn the engine into scrap and to me too high a price to pay just to save a few bucks.

The water control valve is the true stat on a Versa with two of them, the lower one is simply a switch that makes sure when the upper opens it has water from rad. Other than that it really serves no purpose and a stupid design. The Fords use the exact same cooling diagram yet the rad has that lower stat missing as it is kind of worthless located there. If the upper water control valve is closed the engine cannot get any coolant from the radiator anyway, so why the extra part?