Increasingly stringent fuel economy and emissions regulations around the world have forced the further optimization of nearly all vehicle systems. Many technologies exist to improve fuel economy; however, only a smaller sub-set are commercially feasible due to the cost of implementation. One system that can provide a small but significant improvement in fuel economy is the lubrication system of an internal combustion engine. Benefits in fuel economy may be realized by the reduction of engine oil viscosity and the addition of friction modifying additives. In both cases, advanced engine oils allow for a reduction of engine friction. Because of differences in engine design and architecture, some engines respond more to changes in oil viscosity or friction modification than others. For example, an engine that is designed for an SAE 0W-16 oil may experience an increase in fuel economy if an SAE 0W-8 is used. However, if this same SAE 0W-8 oil is evaluated in an engine designed for SAE 5W-30, friction may increase and fuel economy could actually worsen. This hypothetical example illustrates the need for optimization of engine oils to specific hardware. In this paper, a motor-driven engine test is developed to investigate the effects of specific engine component friction on total engine friction. This data is then combined with the work from two previous papers to select an engine oil that optimizes fuel economy in a specific engine. Fired engine and vehicle test results are then presented that demonstrate the fuel economy improvement from the optimized engine oil.