In a heavy commercial vehicle, the engine cooling package is designed by considering peak heat load on the vehicle cooling system from an engine end. In cooling systems, the major unit that consumes most power from the engine is the engine cooling fan. It was seen from the vehicle measured duty cycle data, for most of the time engine operates at part load condition. Regardless of demand from the engine cooling system, engine fan was operating continuously at equivalent speed of the engine. This results in continuous consumption of productive engine power from the fan end ultimately affecting vehicle fuel economy.The present study shows that low idle speed viscous fan has the potential to meet stringent engine cooling performance requirements and consumes less engine power throughout an actual vehicle duty cycle. Experiments were conducted on test vehicle with different fan speeds. At the end of these experiments, it has been concluded that the test vehicle fuel economy was improved by 3% with respect to base results.