The analysis report of used Synthetic gear oil(VG 1000) indicated a high copper corroision(4a), while TAN and the viscosity drops slightly,this oil is only used for 2 days.

Please help to comment the above report.

If there is activity sulfur in the additive in gear oils, it could cause the copper corrosion.

by reductionin TAn the active sulfur has reacted with the Metal.

be careful

EP (Extreme Pressure) oil has sulfur or chlorine composition, which will react with metal at working temperature, said 60C, to form protective surface. Corrosive sulfur test (ASTM D130) normally is used for fuel. It's probably not very suitable for EP lubricants. It may be normal for your oil to be corrosive, if your application need EP oil. However,without detail information about your application, oil name, etc.,it's not easy to answer.

Regards,