Active control of engine-cooling systems over the full range of operating conditions including warm-up, peak-load, and part-load conditions is a fundamental requirement for today's advanced thermal management systems. The controllable Variable Flow (CVF) cooling system described herein combines efficient hydrodynamic performance with modulated output and flow control. Conventional hydrodynamic layouts for engine-cooling pumps are based on a uniform spin-free fluid flow into the impeller. This CVF system introduces an upstream pre-swirl to the flow thus changing the pump output, its magnitude is controlled in response to the varying heat rejection requirement thus providing efficient cooling on demand, for all operating conditions. The underlying principles, development test results, and the benefits for both gasoline and diesel engine cooling systems are presented and explained.