Global warming due to exhaust pollution and rapid depletion of petroleum reserves, has given us opportunity to find bio fuels. Bio diesel is an alternative diesel fuel that can be produced from renewable feedstock such as edible and non-edible vegetable oils, wasted frying oils and animal fats. Bio diesel is an oxygenated, sulphur free, non-toxic, biogradable and renewable fuel. Use of karanja oil methyl ester (KOME) biodiesel in a compression ignition engine was found highly compatible with engine performance along with low emission characteristics. A Military 780 hp, CIDI engine was operated using biodiesel (KOME) and diesel fuel respectively. These were subjected to 100 hours long term endurance tests. Lubricating oil samples drawn from engine after a fixed interval (20 hours), were subjected to elemental analysis. Metal debris concentration analysis was done by atomic absorption spectroscopy. Wear of metals were found to be about 30% lower for biodiesel operated engine. The additional lubricating property of biodiesel fuel due to higher viscosity as compared to diesel fuel resulted in lower wear of moving parts and thus improved the engine durability with a biodiesel fuel.