A heat exchanger (10) according to the invention in the form of a plate comprises a plurality of cooling plates (20, 22, 24) arranged parallel to one another and connected to one another in such a way that cooling flow channels extending parallel to a direction of extension of the cooling plates extend between the cooling plates (20, 22, 24) (30, 32) extending transversely with respect to the extension directions of the cooling plates, the channel (30, 32) passing through a channel (30, 32) passing through the cooling plates (20, 22, 24) (46) which can be closed by means of a regulating element (56), in such a way that at least a partial quantity of the fluid to be cooled flows through this cooling plate into at least one cooling flow passage Bypassing bypass channel (52).