Thermometer seemed good, and the temp gauge agrees. I just drove the truck again, same thing. Spikes to 210 degrees or better and quickly drops back to 180-190 when it finally opens.
Some of my crap:
1963 C-30 flatbed dually 292/SM420
1965 C-10 LWB fleet 250/column shift 3 speed
1965 C-30 9' stepside 250/SM420/4.10 gears (my DD)
Website I made for my crap:
http://www.66submarine.com