MRO Magazine

How to get the most out of your grease


June 1, 2005
By PEM Magazine

A lab technician tests grease from a problem bearing and finds that, although the grease meets all specifications, it’s not performing as it should. A hot-strip steel mill changes over to a grease that has won high praise from other mills, but complaints are pouring in.

During a rush production run, a critical motor fails, even though it has been properly lubricated as specified in the maintenance manual.

What happened? In every case, the company had changed from one grease that met specifications to another type, which also met specs. All were victims, however, of grease incompatibility. Some grease can’t be mixed with others, even when both types meet specifications. And unless incompatibility is understood and accounted for, a switch to a different grease can be disastrous.

Incompatibility occurs when a mixture of two greases shows properties or performance significantly inferior to those of either grease before mixing. Some grease bases are intrinsically incompatible. Different fatty acids and/or additive packages also affect compatibility. To make it even more confusing, sometimes two types of greases are manufactured as a mixed-base grease, although they’re incompatible when mixed in operation.


Usually, problems aren’t obvious until the bearing is in use. By this time, however, they can be serious. It’s best to know in advance which types of greases can be used together and which shouldn’t. Why doesn’t everyone see more problems when greases are mixed either deliberately or accidentally? Even a soupy mix of incompatible greases may work for a while when the bearings are in good shape if shock loading isn’t too severe, the seals are adequate and demands aren’t extreme.

What if changing the grease is necessary? There are ways to ensure a safe changeover:

  • Ask the supplier about compatibility. It should have the information or be willing to run tests;
  • Use up as much of the old grease before bringing in the new grease. If possible, completely drain and clean the system before changing over; and
  • Once the new grease is added, grease consumption should be increased temporarily. This will move the interface (the area of grease mixing) through the system and out as quickly as possible. The increased grease flow also assures good lubrication and proper sealing, while overly soft grease may be in the bearing.

Courtesy of NSK Canada Ltd. For more information visit