Degradation of Gear Oils

The first set of additives to decrease in gear oils is often the antiwear or extreme pressure additives. This is no surprise, as these oils are subjected to high levels of wear and must withstand extreme pressures. One can also notice a decline in the rust and oxidation additives or even a change in the air release values.

 

All these properties significantly impact how a gear oil functions. As such, they should be monitored when establishing the health of the oil.

When monitoring the health of these lubricants, some guidelines can be utilized. If there is a change in viscosity of either ±10%, one should look for any other correlating changes.

Typically, if the viscosity increases by 10%, we’re looking at increases in wear metals or the risk of oxidation and development of some deposits in the oil or even contamination of the oil with some water. However, for a decline of 10%, one can expect some form of contamination, typically fuel or another substance which will thin out the lubricant.

The lubricant’s warning levels for wear metals will vary depending on the manufacturer/OEM. However, any consistent rise in wear metals indicates that some component on the inside of the equipment is slowly wearing away.