Emerging trend in the automotive industry all around the world is to develop vehicles to consume less fuel and to meet stringent emission norms by using engines of higher power to weight ratio and higher thermal efficiency. These advanced technology engines designed for high power output will use low viscous oil to reduce frictional losses and will operate at elevated temperature levels. Hence, the various auxiliaries and parts of these engines should be adaptable for the use of low viscous oil and should withstand higher temperatures. Oil pump is one such auxiliary which will be subjected to work with low viscous oil at higher temperatures levels. The oil pump taken for study and design improvement is an internal gear type positive displacement oil pump, used in a passenger car diesel engine. The un-meshing of the gears causes the inflow and meshing causes the outflow of lubricating oil. This process occurs continuously for providing a smooth pumping action. The oil pump designed for higher viscous oil will exhibit low performance when low viscous oil is used. The performance of these pumps will further go down at the elevated thermal levels of engine. The parameters selected to study this effect on oil pump performance are i) Clearances between the moving elements and the housing, ii) Passages for flow of oil inside the pump and from the pump to the engine. Each element was modified and the pump with the modifications- separately and in combinations-was tested for flow and pressure characteristics. From the experimental results, it was observed that the Oil flow rate improved around 15% for the given pressure specifications with the modification of the design parameters. In addition to the flow improvement the power consumption by the oil pump decreased by more than 15%.