I have had issue after issue after adding aluminum heads to my 400 sb. It just ran hot. I pulled the thermostat and it loved it ran fine 170-180. Now I just put in a mr gasket high hp open flow thermostat. It now runs 190-200 which is a bit better than the 170 range. What I don't understand is the temp is the same in town as it is on the highway? sometimes it goes lower especially when I'm going down hill??? It appears to be ok but I would expect highway speed to provide better cooling with the air flow. I have a brass 4 core with a shroud and flex fan. This week I'm putting a bigger flange 2 core aluminum radiator in with a full shroud and 17 inch fan. Any ideas?

Cleaqrly it means tht you have adequate airflow even at low speeds and the temperature stays constant. System works and is stable.

Now, why are you changing it?