Flushing my cooling system, 200 cid 6 cyl, 1966, 3 speed, and it looked like it hadn't been serviced in a while. Thermostat stuck open along the way, so I pulled it. Surprised to see that it's a 195-degree (unusual looking, too, with the spring sort of enclosed in a casing). All summer, the temp guage always showed a consistent location about one-third the way over off the cold peg at regular operating temperature. What should I replace it with...I'm thinking 180 is safest. Thoughts?

 

Will allow your cars cooling system to be at its best.

 

That engine runs well at 190. A 180 opening will give you heat for your interior heat, and the basic engine heat for operating temps.