After replacing my car's radiator, it still overheats. It's making a hissing noise.
The hissing sound you are hearing is most likely a source of a leak in your cooling system. I would recommend having a cooling system pressure test performed on your vehicle by a qualified technician. This pressure test will pressurize the cooling system without the engine running to make the leak source more obvious to the technician. Once the leak source is found, have it repaired and be sure to have all the air bled from the cooling system afterwards. Once these procedures have been completed the engine should no longer make any noise or overheat.
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