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Hello, my name is Bobby. Thank you for the question. This can be a fan issue if they are not coming on high or it can be caused by a failing thermostat. If it is fine at higher speeds then most of the time it is the fan. Does the fan speed up when the a/c is turned on?
The temperature should not rise that much if they are on at all. You need to replace the thermostat first. If you do not want to replace it as the first step I would do a block test with a test kit from an auto parts store. This engine is notorious of having a leaking head gasket causing this.