In tropical conditions, twelve numbers of ten ton intermediate commercial vehicles run at regular interval from zero to 60000 kilometer. Vehicle field run data were composed and analyzed with intended duty cycle for engine oil drain life estimation.The intermediate commercial vehicle trucks with sump capacity 0.083- 0.104 liter/HP and SAE 15W40 viscosity of oil meeting API CH-4, API CI-4+ from group-I and group-II base stocks are considered. The engine wear is more a function of silica concentration, load factor and age than the API category of the oil. Oil drain interval is found to be proportional to the sump volume for the same stress on the oil. Iron concentration and kinematic viscosity decide to be useful oil life with respect to the limits fixed by the engine manufacturer. In tropical conditions, field trials are carried out on 10 ton payload vehicles at higher temperature, humidity, dust levels and payload factor. API CI-4+ oil provide higher level of protection against soot related viscosity increase and viscosity loss due to shear. Kinematic viscosity @100 degree Celsius is within the limiting range of 11.5 to 18.5 centistoke. Total base number of a minimum of 9 and Max 11.5 is sufficient for BS-III and BS-IV fuel without affecting the oil drain interval. Wear elements like ferrous; copper; chromium; lead; aluminum and silicon Dirt (external) are also within limits. The analysis shows that the CI-4+ oils are best suited for the subject engines.The fresh new oil filter and oil filter run on reliability vehicle has been tested on filter test rig and comparative data have been analyzed. Also the effect of organic sludge; such as unburned fuel, soot, fuel deposits; solvents; and inorganic contamination; like dirt, dust, core sand and wear metal contamination on the filtration of engine oil have been investigated. Pressure drop across the filter and dust holding capacity were measured with respect to oil flow rate and analyzed.