A multi-mode powertrain system is described, and includes an internal combustion engine having stop/start capability. A method for controlling the multi-mode powertrain system includes circulating coolant to a heater core via an engine fluidic circuit that includes a water jacket of the internal combustion engine when temperature of the coolant is less than an engine fluidic circuit upper temperature threshold and the engine is in an ON state. Coolant is circulated to the heater core via a bypass fluidic circuit that excludes the water jacket of the internal combustion engine when temperature of the coolant is greater than a bypass fluidic circuit lower temperature threshold when the engine is in an OFF state.