I had a similar issue with my current car.
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Took a long time for the needle to rise and rarely went higher than your picture.
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It turned out to be the temperature gauge sender.
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Easy cheap fix and now the needle gets up to just under half way within about 5 minutes of driving and stays rock solid.
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If the radiator gets hot enough after a run that the rad fan comes on and the heaters get hot then suspect the sensor.
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Obviously if it's erratic it could be a stuck open thermostat or possibly air in the system
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(had that on my first NA
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- turned out to be a pin hole leak on the rad).
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Are you losing any coolant?