Heat exchanger comprising: a coolant housing having a border which defines an opening; and a header plate arranged to cover the opening; wherein the header plate crimps the border of the coolant housing by encompassing a free edge portion , an outer side surface portion and an outer upper surface portion on at least two opposing locations on the border ; whereby a closed cavity for coolant is defined by the coolant housing and the header plate ; and wherein the header plate is provided with apertures , each aperture receiving a tube for guiding coolant from or to the closed cavity ; the heat exchanger further comprising: a reinforcing plate extending between two opposing locations on the border of the coolant housing , and extending on the outside of the header plate in view of the closed cavity , the reinforcing plate being made of the same material as the header plate and the tubes ; wherein the reinforcing plate is joined, at each of said opposing locations, to an outer surface portion of the header plate encompassing a corner C2 between the free edge portion of the coolant housing and the outer side surface portion of the border ; wherein the reinforcing plate is provided with at least one aperture embracing more than one of the tubes which are received by the header plate ; and wherein the reinforcing plate is arranged to provide a gap between the reinforcing plate and the more than one tubes embraced by the apertures of the reinforcing plate . a coolant housing having a border which defines an opening; and a header plate arranged to cover the opening; wherein the header plate crimps the border of the coolant housing by encompassing a free edge portion , an outer side surface portion and an outer upper surface portion on at least two opposing locations on the border ; whereby a closed cavity for coolant is defined by the coolant housing and the header plate ; and wherein the header plate is provided with apertures , each aperture receiving a tube for guiding coolant from or to the closed cavity ; the heat exchanger further comprising: a reinforcing plate extending between two opposing locations on the border of the coolant housing , and extending on the outside of the header plate in view of the closed cavity , the reinforcing plate being made of the same material as the header plate and the tubes ; wherein the reinforcing plate is joined, at each of said opposing locations, to an outer surface portion of the header plate encompassing a corner C2 between the free edge portion of the coolant housing and the outer side surface portion of the border ; wherein the reinforcing plate is provided with at least one aperture embracing more than one of the tubes which are received by the header plate ; and wherein the reinforcing plate is arranged to provide a gap between the reinforcing plate and the more than one tubes embraced by the apertures of the reinforcing plate . a reinforcing plate extending between two opposing locations on the border of the coolant housing , and extending on the outside of the header plate in view of the closed cavity , the reinforcing plate being made of the same material as the header plate and the tubes ; wherein the reinforcing plate is joined, at each of said opposing locations, to an outer surface portion of the header plate encompassing a corner C2 between the free edge portion of the coolant housing and the outer side surface portion of the border ; wherein the reinforcing plate is provided with at least one aperture embracing more than one of the tubes which are received by the header plate ; and wherein the reinforcing plate is arranged to provide a gap between the reinforcing plate and the more than one tubes embraced by the apertures of the reinforcing plate . <EOS>