The vegetable oil has become a frontier area of research in rural and remote areas for small or decentralized power generation applications. However, the biggest challenge in use of straight vegetable oil (SVO) in a diesel engine is the problem of injector deposits. Soy-lecithin has been identified as bio-additive to overcome the deposits problem due to its natural surfactant and emulsifying properties. Though short-term performance test using soy-lecithin as bio-additive with non-edible karanj oil showed quite good results, its effect on engine performance during long-term test needs to be experimentally investigated for its reliability. The key objective of the current work is to examine the performance of diesel engine operated with karanj oil (Pongamia pinnata) by adopting a novel strategy of periodic dosing of bio-additive during a long-term test. This study also intends to focus on lubricating oil analysis to evaluate the effectiveness of soy-lecithin as bio-additive with karanj oil. Longterm engine test was performed on a Cummins DXP, direct injection diesel genset at a constant speed and load for 130 h. A test was conducted by adopting a novel strategy of periodic dosing of bio-additive in karanj oil in a repeated cycle during engine running condition. Experimental results showed that immediately switched over to additive improved the performance of engine but its continuous use lead to degradation of engine performance. Thus, running of engine continuously with either additive or w/o additive independently would lead to degradation of the engine performance but with periodic dosing of soy-lecithin as bio-additive improved the performance of the engine. The present work suggests the strategy of running the engine with bio-additive in discreet dosages for 2 h after every 7-8 h of engine run without additive in a repeated cycle. This approach would lead to smooth running of the engine which is an improvement over the baseline performance of karanj oil either with or without soy-lecithin alone. The lubricating oil analysis revealed the normal physicochemical properties and normal wear metal level within the discarding limit after 130 h of the long run test. The information coming out of this research would be helpful to researchers working with SVO to overcome the engine problems for its long-term durability or endurance test by adding an additive in a strategic manner.