weirrd cooling system issue with small block chevy

If you have the correct "valved" radiator cap designed to use with a closed system, I fill mine at the cap...all the way to the top, burp it several times to make damn sure there's no air and then cap it off. Any coolant expansion will bleed off into the tank, when everything cools the coolant will contract and create a negative pressure in the radiator which will pull open the recovery valve ****ing the coolant from the recovery tank back into the radiator.

I ran my '35 sedan with this system out to Boron for the "Tossing of the Rod" event and it never got over 190 degrees (with a 190 'stat).

 

After filling the radiator when cold, fill the puke tank only 1/4 to 1/3 full. When the t-stat opens it will add to the volume in the puke tank. When the radiator cools after shutoff, the rad cap allows coolant to be drawn back into the radiator. Without the puke tank, you'll be chasing low water level in the radiator.

 

Have had the same issues with various small blocks. The new thermostats seem to go full open and full shut causing wild temp. swings--get a quality unit. regarding timing--as someone mentioned, you should run a vacuum advance to lower temps in normal operations--makes a big difference. There are many vacuum advance cans--most stockers I've tried don't fully advance until around 20 inches of vacuum. You can find some that are all in at 10 inches which work with after market cams. I have one in my 55 now--the stocker didn't go full advance until 20 inches but with the cam my max. vacuum was 15-16 inches so it would only advance about a 8 degrees at the crank--with the other one it's all in as stated. The one I now have has #BT 28--the one that needs higher vac. is BT 1--also it's easy to check function--some will hold vacuum but not advance-try it with vacuum pump for function.