For hybrid applications it also can warm the battery pack. The cooling system is connected to a heat exchanger placed in the exhaust gas transferring the thermal energy from the exhaust gas to the cooling system. When the engine is warmed up the exhaust gas is diverted to a by-pass pipe. http://gmauthority.com/blog/2015/04/2016-chevrolet-malibu-hybrid-exhaust-gas-heat-recovery-feature-spotlight/