Preheater for preheating the fuel of an internal combustion engine with a heating medium, comprising: - a fuel transport unit with a fuel inlet and a fuel outlet as well as a fuel transport duct connecting the fuel inlet and the fuel outlet; - a heating medium transport unit with a heating medium inlet and a heating medium outlet as well as a heating medium transport duct connecting the heating medium inlet and the heating medium outlet, and/or at least one heating element, wherein the fuel transport unit and the heating medium transport unit and/or the at least the one heating element are in thermal contact with one another and thus form a heat exchanger, via which a fuel transported in the fuel transport unit can be heated by the heating medium transported in the heating medium transport unit, and/or by the at least one heating element, and wherein the heating medium transport unit and the fuel transport unit are arranged in a metal block and the fuel transport duct 25, which is arranged on a first side of the block and incorporated, milled or inserted in the metal block, and the heating medium transport duct arranged on a second side of the block, in particular opposite the first side and incorporated, milled or inserted into the second side, are each formed in the block with separate flows from one another in meander fashion in at least some portions, and/or the fuel transport unit is arranged in a metal block and the fuel transport duct incorporated, milled or inserted in the metal block is formed in meander fashion in at least some portions and the at least one heating element is arranged in or on at least one cover plate (11a, 11b) of the metal block, characterised in that the metal block contains copper or is made from copper, and that the fuel transport duct or the fuel transport duct and the heating medium transport duct is/are covered by in particular in each case at least one cover plate (11a, 11b), in the centre of which there is an elongated hole or an elongated depression which is placed in form-locking manner over a projection or guide web which is provided on an open side of the block on a centre web. - a fuel transport unit with a fuel inlet and a fuel outlet as well as a fuel transport duct connecting the fuel inlet and the fuel outlet; - a heating medium transport unit with a heating medium inlet and a heating medium outlet as well as a heating medium transport duct connecting the heating medium inlet and the heating medium outlet, and/or at least one heating element, wherein the fuel transport unit and the heating medium transport unit and/or the at least the one heating element are in thermal contact with one another and thus form a heat exchanger, via which a fuel transported in the fuel transport unit can be heated by the heating medium transported in the heating medium transport unit, and/or by the at least one heating element, and wherein the heating medium transport unit and the fuel transport unit are arranged in a metal block and the fuel transport duct 25, which is arranged on a first side of the block and incorporated, milled or inserted in the metal block, and the heating medium transport duct arranged on a second side of the block, in particular opposite the first side and incorporated, milled or inserted into the second side, are each formed in the block with separate flows from one another in meander fashion in at least some portions, and/or the fuel transport unit is arranged in a metal block and the fuel transport duct incorporated, milled or inserted in the metal block is formed in meander fashion in at least some portions and the at least one heating element is arranged in or on at least one cover plate (11a, 11b) of the metal block,