Effect of ageing automotive gear oils on scuffing and pitting

The aim of this work is to compare automotive gear oils of different performance levels (API GL) from the point of view of their resistance to degradation due to ageing. The influence of the gear oil degradation on scuffing and rolling contact fatigue (pitting) has been assessed. Two automotive gear oils of API GL-3 and GL-5 performance levels were tested. They were contaminated with dust, water and oxidation residues.It has been concluded that from the point of view of the resistance to scuffing the most dangerous contaminant is water. For the resistance to rolling contact fatigue the most dangerous are dust and water. In general, GL-5 oils are less vulnerable to deterioration due to ageing than GL-3 oils.