Radiator Overflow Puking at low temps?

[Xavier]

A year ago I was running a traditional overflow tank on the inside fender, a single 22psi radiator cap and a 50/50 mix of fluid and water with the same 190F thermostat I have today. With the use of the traditional looking push fans in front of the radiator and the puller behind it never over heated. I turn them on when necessary manually. At this time I had a 4 barrel carb.

Currently I am running with a Kirkrham FE style overflow tank with (2) 18psi caps (recommended PSI by KMS) one on the radiator another on the FE style tank. I run straight water with water-wetter. Same 190F thermostat with (2) 1/8" holes in it. I also went through a Weber 48IDA conversion (which I do not think make a difference in the problem but...).

In a 30 minute drive at 68F outside driving at 65mph to 80mph with 80c to 90c on my water-temp gauge the top line out of the KMS overflow tank is puking fluid underneath the engine. The fans of course were never turned on at these temps, why would I need to?

What the hell is going on?