The temperature gauge in my car is rising when I idle or have the AC on. I found a crack in the radiator and had it sealed in the meantime.
When your engine is idling, the vehicle is likely stopped which lowers the airflow through the radiator. The more airflow the radiator receives the more likely the engine is to remain cool. When the air conditioning is turned on the engine must work harder to run the A/C compressor and will therefore heat up more. A coolant leak in the radiator is most likely the cause of your issue. At the soonest possible moment I would recommend having your radiator replaced in order to prevent engine damage from overheating or being stranded on the side of the road.
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