shell 3 and the housing shell 5 so that a switching of a bypass flap element 43 of the bypass flap 33 is dependent on the temperature of the coolant flow the housing shells 2 3 4 5 are connected respectively via grooves 44 in which bars 45 of the respective other housing shell 2 3 4 5 engage whereby the permanent connection is achieved by adhering at these points in order also to connect the housing shells 4 5 in this manner the adhesion point with the grooves 44 and the bars 45 should be displaced in the area of the coolant jacket 42 for this purpose an extension in the form of a flange can be embodied at the ends of the housing shells 4 5 lying on top of one another at whose ends pointing towards the heat exchanger unit 15 a groove is formed in both housing shells 4 5 so that an air space is formed between the adhesion point i e in the area of the groove 44 and the bar 45 which air space protects the adhesion point from too great a thermal load from the exhaust gas this is not shown in the figures moreover it can be seen from fig1 that on the connector valve 19 a seal 46 is arranged via which the housing 18 22 against the connector housing part 25 in which the seal 46 is arranged in a groove 47 is sealed against the atmosphere an additional sealing ring 48 is arranged in a groove 49 formed at the upper and the lower outer housing.