The steam is likely causing you the issue. I don't like the location for actual engine temperature either. You want to know how hot the coolant is in the engine, not after being cooled by the radiator.
That temperature sensor is for the fan controller. His temperature gauge is likely on the driver side head.
Pretty sure you have air trapped in the system based on your description of how you filled your system. You did not burp it....
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
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