Plate heat exchanger without casing

The motor vehicle exhaust gas heat exchanger has a flow switching valve (20) in one manifold (4,5). At least the main part of the gas stream passing through the cooled flat tube (3) or through at least one non-cooled flat tube is steerable via the valve. Separation between the cooled tubes and at least uncooled tube is through a closure for the channels in at least one of the plates (1,2).