Does lubricating grease “go bad” if it is stored for too long?  How long can unused grease be stored?

Unused lubricating grease can “go bad” if it is stored for an excessively long period of time, or under poor storage conditions.  Most manufacturers place a date of manufacture on their product labels and publish shelf-life information for their products.  The grease manufacturer’s shelf life guidelines should be followed.  Grease can have a shorter than stated shelf life if it is stored improperly.  Grease containers that are stored outside can accumulate dirt, dust, and water on the lid, which can enter the container during the natural “breathing” that the container does upon heating and cooling.  In addition, as oil tends to separate from grease over time, it can separate excessively if stored for a long time, to the point that the oil cannot be remixed into the grease.  Solid additives can also separate from grease, resulting in a grease that is not suitable for use.  Both the oil and solids separation phenomena can be aggravated by the improper storage of the grease container in direct sunlight or near a heat source.