my temperature gauge spikes high when i don't have my ac on?

Heat underneath the car -- not sure about that. As far as your temperature gauge going up without your air on -- your blower in the vehicle can at times act like a little cooling fan for the coolant passing through the heater core, even though the blend door is turned to cold. It's just a guess, but I would check for proper operation of your cooling fans at your radiator, and even check for any debris at your radiator or any air flow restrictions. Obviously, other temperature related diagnosis testing should be performed for the engine, making sure the thermostat opens and closes as it should and so on.