Abstract:The vehicle engine can obtain more dynamic and economy by using low viscosity engine oil.By taking the 1.5 L—L4 naturally aspirated gasoline engine for an example,the influence was studied on engine performance by using low viscosity oil SM 5W20 to replace SM 5W30.By using the lubrication system model of engine established by Flowmaster software,the influence of oil viscosity on pressure,flow and oil pump power dissipation of engine lubrication system was analyzed.It is showed that,oil flow of the system is increased by 0.83%—6.72% ,oil pressure is decreased by 1.45%—5.98% and oil pump power dissipation is decreased by 1.4%—6.58% by using low oil viscosity of SM-5W20 to replace SM-5W30.The influence oil viscosity on engine friction,power,torque and fuel consumption was studied on engine test platform.The results show that,engine friction power is more lower by using SM-5W20 than using SM 5W30,and engine fuel economy is improved in the low to middle speed.