Abstract: The invention relates to a device (1, 11) for cooling a coolant by heat exchange with another fluid, that comprises an inlet and at least two outlets (3, 4) provided at different levels for over-cooling the coolant. The device (1, 11) is characterised in that it comprises a modular structure including at least two modules (5, 6), each module (5, 6) including at least one outlet (3, 4), and in that both modules (5, 6) are hydraulically connected together by a male end-piece (7) of a first module interacting by insertion with a female end-piece (8) having a complementary shape of a second module (5).