Hi Ron. Since I built your car Ron - and Sandy's, Spooky's and many others - I thought I'd tell you what I know. Your temp gauge is mechanical and could have gone bad, I've seen it a few times. Putting the sending unit in boiling water is a good test but your sending unit isn't very easy to get to. The SPF cars have a provision for the
oil temp sender in line with the cooler and filter and give a quicker more accurate reading. Since your car is a CSX it doesn't have this provision and the sending unit is mounted in the
oil pan. This setup always took longer to get a reading on the gauge. I would try checking your gauge on a longer run to see if or how much the needle moves as a first step.
Please let me know if I can help.