misreading temp gauge

I'll pick up some resistors and get out my multimeter. I just thought there might be a common fault with these as they age. Still don't get the connection with the fuel gauge. Of course, they are both powered by 12v, but are two separate systems - aren't they? What's an IVR? Voltage regulator?

I'm pretty sure that, given my infrared reading, the gauge is wrong; also I drove it 200 miles home with it showing 3/4 hot and it never boiled. Also noted while after taking my reading, after I put the cap back on, I have a pinhole in the tank. Ah, well, it's 50 years old, there WILL be issues.

Never had a slant let me down yet.