Chevrolet Captiva Radiator Problem

I'm having a problem with the radiator in my Chevrolet Captiva. It appears that there may be an issue with the radiator not receiving water. As a result, I find myself needing to release air from the car's water tank whenever I go for a drive. Not doing so results in an increase in engine temperature. Whenever I let out the air, water flows into the radiator. The mechanics at the repair shop were unable to identify the issue, even after replacing the circulation pump and radiator. If anyone has encountered this problem previously, I would greatly appreciate your insights.