Blueprint 408 cooling system questions.

Johnny Mac said

Have you topped off the radiator after it has cooled all the way down? Several times?
Tried leaving the radiator cap off (from cold) and seeing it the t-stat opens properly and you can see the fluid moving? And top it off if low.
Note, you do have to get the cap on before it hits boiling....so it doesnt geyser.

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Agree with Johnny Mac, take that rad cap off and fire it up. When you see the fluid moving take note of the temp gauge. Now, make sure you have the front end on jack stands, that will purge any air in the system out of the rad opening. Air in the fluid equals steam and that will drive up the temp.
There is another school of thought that says go with a 165 degree thermostat. The thinking is that it will open sooner and get fluid moving before temps creep up.
I use a 165 t-stat on my 455 Firebird, because it has iron heads and Ross flat top pistols (no relief cut in them at all, true flat tops) making around 11:1 compression. So that engine runs warm. But between the t-stat and the 1.25" tubes in the rad, all is good.