a heat - exchanger tank consisting of a cover and a plate fixed at the opening of the cover , the plate being elongate and u - shaped , having a web portion and two flanges ; and the cover consisting of a u - shaped middle piece fixed with its flanges to the plate flanges , and two separately manufactured cup - shaped end pieces , the mouths of which are u - shaped for connection to the respective end of the middle piece ; and the end piece having two guide flanges connected to the flanges of the plate and arranged so as , when the heat - exchanger tank is mounted , to guide the end pieces into correct alignment with the middle piece .