The invention relates to an outer pipe (1) of an outlet (4) of a volute (3) of a heat transfer pump (2), particularly arranged in a recess defined in a heat engine of a vehicle, the outer pipe (1) being provided on an outer surface (9) of the cylinder housing (8) of the engine and comprising a first component (5a) capable of guiding the heat-transfer fluid from said outlet (4) to an inlet (6) of an inner circuit (7) for circulating the heat-transfer fluid defined in the cylinder housing (8).