Bert's explanation is slightly different to the version I heard: The swirl pot was added to reduce thermal shock to the radiator when the thermostat opens and suddenly floods the cold metal with piping hot coolant. Both seem possible and are not mutually exclusive of course.
That sounds closest to its intended function and concurs with the explanation given by a dealer, temperature rather than physical flow shock.
Richard
2018 Roadster 3.7 1966 Land Rover S2a 88 2024 Royal Enfield Guerrilla 450 1945 Guzzi Airone
