New for 2025
Ask the Expert is a feature that expands on real-world technical questions submitted by individuals, detailed, in-depth answers are provided from industry professionals. It not only addresses the query at hand but also delves into the underlying concepts, practical applications, and best practices, offering a comprehensive resource for anyone seeking to understand and solve issues related to lubricants and grease products.

Ask the Expert Question: 

Q: Sometimes when a container of grease is opened, there is noticeable oil sitting on the top. Is that a problem and would there be consequences to using it? Is there a certain amount of time when this noticeable oil present, that the product shouldn’t be used? Finally, could NLGI provide a reference source that discusses this sort of occurrence?  

A: A common term used to describe the presence of oil, as described, is oil bleed. A small amount of oil sitting on top of, or in voids within, greases are not uncommon. Grease bleed can sometimes be worse with softer penetration grades or with some thickener types vs. others. A good recommendation is to contact the manufacturer of the grease if the amount of bleed seems excessive. They would have good familiarity with what is a normal amount of bleed for this grease. Based upon that, they would also be able to make a recommendation whether it is safe to use the grease and how to manage the bleed. Various things have been recommended, such as pouring off the excess oil or mixing it into the grease prior to use. Some may determine it is too much and recommend replacement of the grease. 

A second part of this question was asking whether there is a certain amount of time that grease can be stored before the grease bleed occurs and after a certain amount of time it should be discarded. The term for this is sometimes called the product “shelf-life.” Once again, shelf-life seems to be variable from manufacturer to manufacturer and possible even from product to product from the same manufacturer. Therefore, when in question, ask the grease manufacturer for advisement on this subject. Although some may have an established shelf-life, it may not mean they will suggest the grease must be discarded. They may recommend testing to requalify it. Shelf-life can be heavily dependent upon the storage environment; indoors, vs. outdoors, extreme heat or cold, etc.

Finally, the third part of this question was whether NLGI could recommend a reference to learn more about grease bleed. There is an ASTM standardized test method, D1742 Standard Test Method for Oil Separation from Lubricating Grease During Storage. This method is used to evaluate the tendency of a grease to separate oil during storage in filled and partially filled containers. This method is not recommended for any greases softer than an NLGI Grade #1. Many grease manufacturers are familiar with this test and may even possess data for some of their greases. Another source of grease information, including for information on bleed, consult the NLGI Lubricating Grease Guide.

Bottom line, some bleed is normal, too much may be a concern. When in doubt, contact the manufacturer for further advice.