●  Grease Separation – Oiling
Specific performance: The grease becomes thinner in consistency and flows out from the bearing.
Reason: The grease can not withstand high temperature and shear environment for a long time, the structure of soap base in the grease is destroyed, the oil and soap are separated, so it is softened and lost.

●  Grease carbonisation – Coking
Specific performance: bearing wear is serious or directly hold dead, similar to dry friction. After opening the bearing, it is found that the grease is no longer in semi-fluid state, instead of black charcoal.
Reason: The hydrocarbons in the grease, which play a role in lubrication, undergo a chemical reaction such as oxidation at high temperatures and eventually turn into carbides.

●  Insufficient lubrication – Wear and Seizing
Specific symptom: During regular maintenance, there is semi-fluid grease on the bearing, but the bearing is severely worn.
Reason: Insufficient lubrication capacity of the grease prevents the formation of boundary lubrication or extreme pressure lubrication between the friction parts. This means that the grease has no or limited lubricating effect and the bearings are still in direct contact with each other.