Realizing that 53 year old guages were not that accurate to begin with and may even be less now, I have a question:
I have a 70 351C with what appears to be the original water temp sender, a Flow-Kooler Robert Shaw 180 high flow thermostat (with brass restrictor "ring"), a replacement (NPD) guage cluster harness, and am drawing power for a Holley with electric choke from the temp guage power wire.
Runs great, no signs of overheating regardless of ambient temp., etc. I generally drive it for 30-60 mins at a time max.
My temp guage needle usually sits on the "C", or slightly past., which I think is a bit low. I let the car idle for about 25-30 mins once and the needle moved almost to half way between "C" and "H"
I think the guage is reading low and am concerned it may be because of the power draw. Do I have a problem, or am I chasing something that isn't there?

Thanks!