receptacle containing an oil exchanger 16 water reservoir 12 is mounted in the traditional manner at one end of a cluster of tubes 18 by means of a collector or tubes plate 20 fig1 cluster 18 in the traditional manner comprises an assembly of parallel tubes 22 which pass through an assembly of radiating flanges 24 which are parallel to each other and perpendicular to the lengthwise alignment of tubes 22 one end of each of tubes 22 is mounted in a sealed manner in holes 26 fig1 formed in the collector 20 at the other end of cluster 18 is mounted a water reservoir 28 provided with an inlet pipe 30 water reservoir 12 of device 10 is provided with a discharge pipe 32 fig3 water reservoir 12 includes a side wall 34 of semicircular upright cross section fig2 which is joined to a peripheral flange 36 which is rectangular having two long sides 38 and two short sides 40 flange 36 with lateral wall 34 thus defines an open surface of rectangular shape which is suitable to be joined in a sealed manner with collector 20 for instance by welding if this collector and the water reservoir are formed of plastic material appended receptacle 14 is of generally cylindrical shape of which the axis 42 fig1 and 2 extends parallel to the two long sides 38 which are defining the open surface of water reservoir 12 appended receptacle 14.