I have the same hood and my 451 (Contour electric fans, aluminum 3-core rad) will idle at 182 degrees in traffic all summer long... but warms up into the mid-to-high 190's when running on the highway at 65-70 mph (3300-3400 rpm)...
It's possible that the open scoop is messing with the airflow through the rad at highway speeds. Haven't gotten around to taping it off to see if there's any difference yet since it doesn't "overheat" ;)
