Finally found the cause of my overheating

toolmanmike said

Fans? It's a 64 Dart with a slant 6. Unless it's a a/c car it has a belt driven 4 blade fan. And as a side note, unless it's puking coolant out all over it's not overheating, regardless of what the gauge says.

Click to expand...

I swapped over to electric fans. So over taxing the alternator and slowing the fans, or current bleed to the gauge are both possible causes. I grabbed a water temp gauge and sensor from work today, so bisecting the issue should be easy. Finding and fixing the possible circuit problem will be more difficult, but I am sure it would be in the dash as it is years of band aids and splices in that rat's nest.