Engine is a complex machine; it consists of a hundreds of moving parts. The parts of engine are operated under a wide temperature ranges and pressure. The basic idea of using oil in any machine is reducing friction and wear, so the friction power drop in any machine depends on oil conditions and specifications, the most important property of oil is viscosity, viscosity shows the amount of forces between oil particles. In this paper experimental apparatus is used to simulate the relation between oil viscosity and temperature, the experiment data are used to produce mathematical formula for different engine oils with different conditions. Engine oils 10W-40, 5W-30, and 20W-50 are selected for testing and simulation because these types are widely used in Kuwait market for engines. The SVM 3000 viscosity measuring unit is used to measure viscosity and density of engine oils 10W-40, 5W-30, and 20W-50 in new and used conditions, the results show that there is no change in oil viscosity for new oil and used oil