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How Much Grease is Too Much for My Electric Motor?


2020-04-lubrication of electric motors-ultraprobe 201 grease caddyYou are responsible for getting as much as possible out of the electric motors in your facility -- and you know that proper lubrication for your electric motors is a big part of that equation. You've heard that there can be issues with too much grease, but how much is too much? And how do you know when grease needs to be added?

The Purpose of Grease

Grease is a semisolid lubricating material comprised of oil suspended in a thickener. Grease does more than just reduce friction in bearings: it helps conduct heat away from the bearing, protects it from contaminants such as dust or moisture, and protects the surface finish by preventing corrosion. The thickener in grease helps it to stay in place and act as a seal for the bearings. Basically, the oil is held within the grease until the motor begins to operate. Once it starts to operate, the oil begins to flow and compress between the various bearing surfaces.

The Results of Too Much Grease

There's an old saying about how you can never have too much of a good thing. Grease is a good thing, but too much grease can result in several issues, starting with an increase in friction -- the very thing that grease is supposed to reduce. This friction leads to elevated temperatures which can cause the oil in the grease to begin to separate from the thickener and lead to premature bearing failure. Overheating will lead to a reduction in the overall effectiveness of the grease. In addition, the presence of too much grease means that the anti-friction bearing elements have to push through this excess grease, making it harder for the bearing to do its job. That means more losses and even less efficiency.

There are more complications that can arise from using too much grease, however. If the grease cavity becomes too full and a grease gun is used to add more grease, that excess grease has to find a place to go. It typically ends up between the shaft and inner bearing cap. Even more pressure is applied by the greasing gun, and that grease will end up inside the motor. Once there, it can lead to more than bearing failures: when grease begins to cover the end windings, insulation failure is not far behind. And that means expensive repairs and downtime.

How Often You Should Grease

Your first instinct may be to follow a certain schedule for how often you grease bearings, but that isn't the best approach because there is more than just time intervals involved. Parameters such as RPM, bearing size, vibration levels, operating hours, environmental cleanliness, and operating temperatures can all impact when you should grease bearings. Tables are available to give you an idea of how often to lubricate based on motor RPM, motor frame size, and operational usage (e.g., 8 hours a day vs running continuously). However, consider these "rules of thumb" as just that and understand that there are many variables.

How Much Grease is Enough?

There are grease tables -- many of which are posted online -- that will indicate the correct amount of grease to use on certain bearings. You can also calibrate your grease guns so that you know how much grease is added per pump. But how can you really know how much grease is enough for your equipment? One very interesting answer lies in the use of ultrasound.

Ultrasonic tools can be used to verify that the correct volume has been added and to provide verification as to how frequently the bearings need to be greased. When grease levels begin to fall, it results in friction; that friction then produces localized, directional waves that can be easily detected with the right equipment.

A skilled technician can formulate a baseline from the ultrasonic data and use it to, over a period of time, determine the optimum amount of grease to use and the frequency at which it needs to be added. The Ultraprobe 201 Grease Caddy is an example of just such technology because it allows you to add grease and monitor the grease levels using ultrasound. This supports predictive maintenance and a much more tailored, effective approach to maintaining your motors and power trains.


There are a host of reasons why you want to avoid over-greasing the bearings in your electric motors. When you take a smart approach, optimizing how much and when the grease is added, you will see an improvement in the useful life of your equipment, better efficiency, and reduced maintenance costs (both in terms of downtime and electric motor repairs).

Author and contact information:

Hunter Shields: 

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