Abstract: A heat exchanger is provided in which two header tanks (11,12) are structurally connected together by two spaced apart casing members (15,16) therebeing a number of fluid conduits (13) to provide a fluid transfer connection therebetween. Each of the header tanks (11,12) includes a plate member (18) a side wall member (19) which defines in combination with the plate member (18) a fluid manifold each end of which is closed by a respective end cap (20A,20B,21A,21B). Each of the end caps (20A, 20B,21A,21B) includes means (25) used during assembly as an assembly aid. A further feature of the invention is the use of extruded material for several of the structural components.