Dependence of thermal stability of an engine lubricating oil on usage period

Mineral oil type lubricating oils have an important role in reducing engine wear. But after some period, depending on the oil quality, oil replacement is needed since the oil loses its properties. In this paper, an engine oil was tested in a 1300 cc engine car and the change of the thermal stability of the collected portions of oil at different usage periods were experimen ted by TG/DTG and DSC techniques. Results show that, as usage period increa ses lubricating oil contains more of the light components that distill at l ow temperatures. The increase in tine peak maximum temperature, T-max, of t he DTG, as usage period increases, proposes that the molecular mass of the oil increase, which presumably changes the viscosity characteristics. Moreo ver as the usage period increases some residue type components, which only can be destroyed at very high temperatures, are produced in oil phase.