ABSTRACT The application of efficient variable output sub-systems for light, medium and heavy duty vehicle propulsion is a common pursuit in the interest of increasing engine performance and efficiency by decreasing parasitic losses. Many modern power steering pumps, automatic transmission and engine oil pumps, and air conditioning compressors provide variable output to meet variable load conditions independent of engine speed. Despite this trend, conventional cooling system pumps are not variable independent of engine speed and coolant flow is throttled by a conventional thermostat. The controllable variable flow (CVF) system described herein combines higher hydrodynamic pumping efficiency with thermally responsive integrated flow control capability thus exploiting the opportunity for fuel savings and lower emissions without requiring increased system complexity, materials, or space required. Comparative fuel economy and emissions testing on a first in-vehicle prototype confirmed 1.2% improved fuel economy plus measured emissions reductions relative to the series production pump and thermostat cooling system. The prototype system installed in a 3.0 litre V6 gasoline powered passenger vehicle has since completed 250,000km of all-season road testing trouble-free. This second paper on this topic reviews the technology, development, and vehicle testing results and also studies the attributes of this technology as applied to advanced internal combustion (IC) and new and emerging hybrid propulsion systems for light, medium and heavy vehicles applications. The hydrodynamic and operational principles, early development and prior test results have also been reported in an earlier paper by Fulton et. al. [1].