What degree Thermostat?

Abarguy said
Unless I missed it, one thing I never see in these discussions is the correlation between thermostat temp ratings and radiator cap pressure ratings. Stock slant 6 from the early 60’s ran 160 thermostats and caps rated at 12-14 psi. Eighties slants ran 180 t-stats and 16-18 lb caps. If you wanna go 195, you’ll need a 19-21 lb rad cap.

I just proved that by replacing the 180 deg with a 200 deg for a better mileage experiment. I opened up the valve lash a bit too for higher cranking cylinder pressure. My shiny, relatively new 12 psi radiator cap now leaks like there is no seal in the cap!