Abstract: A heat exchanger for recovering heat from exhaust gases which includes a plurality of separately divided portions, a fluid passage mechanism for a fluid disposed within each of the portions, a bypass mechanism for the fluid for bypassing each of the portions and a valve mechanism for selectively operating the fluid passage mechanism or the bypass mechanism. The plurality of portions may constitute at least two chambers separately provided in the heat exchanger or at least two parts independently provided ion the heat exchanger. In addition, discharge means for discharging the fluid in the plurality of portions is provided.