In India, there is a large population of heavy duty diesel engine powered vehicles such as trucks and buses. Buses are operated under normal speed & load conditions whereas trucks are generally overloaded with high severity on engine oil and lugging operation is common. Higher loading of soot in engine oil results in increase in viscosity of oil and also affects the friction properties and also wear in engine components. The engine oil keep the soot dispersed in order to meet the basic function of lubricating and also keep the engine components clean.To study the impact of soot on diesel engine oil performance tests were conducted on a turbo charged diesel engine conforming to BSIII for 150 / 250 hours using commercial grade oils with increased test severity by changing the engine design parameters such as injection timing & injection pressure, intake air throttling and also operating conditions such as speed, torque, coolant and oil temperatures in order to generate 6% of soot level at the end of 250 hrs for simulating the field conditions of severe truck operation. For establishing the effect of soot loading on engine oil performance and coefficient of friction of engine oil, total 6 no. of lubricating oil samples were evaluated during the study.This study reports the effect of soot loading on performance of engine oil by analyzing of the engine oil properties and tribological studies using SRV and FZG test rigs. It is observed that there is significant change in engine oil kinematic viscosity with high level of soot loading and increase in co-efficient of friction thereby increasing the fuel consumption and also wear.