My take is water temp is nearly useless, because water boils away at a low temperature, holding the temperature down despite a serious malfunction.
I am talking phase change, latent heat of vaporization, stuff refrigeration folks see all the time.
Then when the water is all gone, the crap has already hit the fan, the temperature suddenly goes through the roof, and the gauge finally pegs.
If you've ever tried to solder copper pipe with the tiniest bit of water in it, you have seen what I am talking about.
I am with Nelstomlinson on this. I'd much rather have oil temp as a proxy for engine block temperature.
It should track as long as I have oil pressure and circulation.
Anyone know a good spot on the 7.3 for oil temp sensor? Also, type K sensors for this kind of thing? You know, correct thread and does not poke in too far.