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?
Line two is wrong and has been wrong. Slowing flow also leaves the coolant in the block to absorb more heat. You want flow.
To the OP I didn't read all this but you need the water pump faster than the crank. You need a thermostat that actually works. I've only found one. That is the Stewart Components thermostats. They open BEFORE the actual temperature so it's wide open at that temp. So...if you have a 180 stat it should be opening before 180 and be wide open at 180.
Also, not a big fan of electric fans. I don't care about CFM. The fan only matters at low road speeds. Once you get past about 15 MPH or maybe even less, the fan is in the way. Your fans are actually blocking air flow. Also, a 3 core radiator is never as good as a 2 core. Two big cores is always better than 3 smaller cores. 4 cores is just silly.
You have a simple problem that comes up. Water pump turning too slow, electric fans, too many cores that are too small and probably a thermostat that doesn't flow enough. It's all about flow. You can't have coolant move too fast. You need the coolant out of the block and in the heat exchanger to cool effectively. So speed up the pump, and get rid of the electric fans.
Edit, I forgot to mention the purpose of the thermostat isn't to slow coolant flow, it's to facilitate quicker engine warm up. Only heating the coolant in the engine is quicker and better on the oil, the block and everything else. That's all the thermostat does. That's it's only purpose. Not to slow the coolant. Although the cheap ones do slow the coolant and that's bad.
