The gauge is supposed to go up, so you have to be more specific. If it's reading higher than normal, does it do that as soon as you start the cold engine, or does the engine have to warm up first? When the heater brings the temperature down, that says the radiator isn't giving up the heat to the air. Corroded cooling fins will do that, but if the radiator was new three years ago, check instead to see if they're plugged with bugs and leaves.
If the car had crash damage repaired, check for the rubber seal under the front of the hood to be sure it's there. If it's missing, air will bypass the radiator.
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Wednesday, December 4th, 2013 AT 9:09 PM