I know this seems like a dumb question, but have you checked for radiator obstructions? You might have picked up some paper or plastic stuck on the front surface of the radiator blocking airflow or something.
230-240 sounds high for highway cruising (6th gear, 55mph+), but it's not a dangerous temperature either. As others said, switching to a better oil and/or putting some more miles on the car might cure it.
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