Lots of great advice. Now here is the correct answer Seriously too.
I had experience with my mother's 94 Ford Contour. Same thing I assume as yours. The Ford water temp guage is not calibrated, that is, showing the actually degree readings. Just shows what normal and hot as I recall. The guage range too is very small, like maybe 20 degrees but you don't know that. So it can take some real wild swings, and the more you now watch it the more paranoid you get. The key is that it never moves out of normal. And yes, sitting at a stop for a minute or so, that thing will climb so much you will panic, but it is OK. If you had the owner's manual, it will basically tell you the same thing
Your Explorer is OK, believe me, but a flush at those kind of miles is never a bad thing either