another 360/408 over heating

Impressive amount of test data, hats off to you.

One of the duties of the thermostat is to slow the flow of fluid so it has time to remove heat from the engine.

I am not a fan of shrouds, especially ones that are flat and close to the rad.

If you have a 16 lb rad cap and no leaks you should build pressure.

Your test that showed exhaust gas in the fluid should be examined with a pressure test.

I wonder if you replaced your fluid with normal 50/50 mix what your results would be.

I'm also not sure that 220 is too high for a properly functioning pressurized system. iirc 16lbs raises boiling point to 250 deg.


Another thought... air full ratio? Are you running lean?