Disclosed herein is an exemplary supplemental heating system including a liquid heat generator having a hydrodynamic chamber for selectively heating a fluid. The supplemental heating system further includes a manifold having an inlet passage fluidly connectable to a discharge passage of a heat exchanger, a first discharge passage fluidly connectable to an engine cooling system, and a second discharge passage fluidly connected to an inlet passage of the hydrodynamic chamber. A control valve comprising a spool slideably disposed within the manifold controls distribution of the fluid between the manifold inlet passage and the first manifold discharge passage, and the manifold inlet passage and the manifold second discharge passage.