Executive Summary
When it comes to oil separation in grease, TLT readers hold a wide range of perspectives on what is and isn’t acceptable. While some readers do not tolerate any separation in a grease, others find this to be a very normal condition and no cause for concern. A large number of readers fall somewhere in between, noting that quantifying the actual amount of separated oil is important. The application where the grease will be used is another critical factor, and the diversity of opinions on this topic likely reflects the many applications with which TLT readers work.

Q.1. Describe how you feel about a small amount of oil separation in a grease tube, and one being able to decant it (pour the oil “off”) and put the tube to work.

Slight concern but the question is what is a “small amount.” A mL or less, not worried.

I think that oil should not separate from the grease. It indicates that the emulsion is unstable. Pouring it off is a workaround.

Would rather mix in to the top with a clean utensil. One should know the product or seek information from their supplier.

This phenomenon makes me skeptical of the integrity of the grease.

So long as the amount of oil separated is not excessive, that is a perfectly normal practice, though not as wise as just stirring the grease a little to reincorporate some of the oil.

A small amount of oil may appear on top of a grease stored in a tube or cartridge, especially after long storage or exposure to temperature swings. This is normal. Grease is a structured blend of base oil, thickener and additives. Over time, a bit of the base oil can migrate out of the thickener matrix, a natural process called oil bleed or syneresis. It does not mean the grease has failed or that it’s unsafe to use. If the oil is dark, sour-smelling or the grease appears dry or cracked, discard the tube then, that indicates oxidation or thickener breakdown. Now excessive bleeding, though, signals the product has aged beyond serviceability.

A certain amount of oil “pop” is usually not a problem. Decanting the oil is not something everyone will do. Some customers just pump it into the application.

If the oil is separating from the grease while on the shelf, you have one of two problems. Either your storage area is not climate controlled or your inventory of grease is too large and not being used quick enough to avoid the separation.

Nonsense, some oil bleed is absolutely normal.

It is normal for this to happen, and the oil will reintegrate into the thickener once it is applied. No need to pour off the oil.

It is common to see a small amount of oil separation. I don’t think it is a good practice to decant the separated oil. In my work the suggestion is to mix the oil back in and then use.

Getting rid of oil from separation from the thickener in a tube causes an environmental problem.
Yes 45%
No 55%
Based on an informal poll sent to 15,000 TLT readers.

This phenomenon is more common particularly with certain types of thickener chemistries. The function of the grease matrix is for the oil to be released onto the lubricated surfaces with temperature and pressure under most circumstances.

I don’t think there should be any oil separation. I know sometimes hot weather temperatures may cause this.

Generally, this is not a deal breaker for myself, and if the bleed is minimal that could be acceptable if the end-use and application calls for a grease that needs some bleed. I look at it on a more case to case basis.

Instead of pouring it off, use a clean rod or clean screwdriver to mix the oil back into the grease.

I see it as a quality control issue. The liquid has a purpose and a role in what makes the grease up, and if it is being separated there is an issue.

Not recommended to see oil separation.

This is normal, if not excessive. PAO-based grease tends to be messy in storage if not properly handled. Decanting? Why would I want to get rid of the essence of the grease?!

Free oil indicates possible poor storage of the grease (too warm storage temperature), but it may also indicate poor manufacturing techniques (too short of a cooking time, but more likely indicates insufficient milling).

Never happened to me. We have very stringent quality control, i.e., expiration date, etc., in place. Don’t let that happen.

It’s something that happens. Usually in the summertime when it’s hot.

This is generally fine. A small amount of separation accounts for only a fraction of the oil phase in the product and should not greatly impact its utility.

I would prefer it be mixed back into the grease. 

No problem, I see it as normal within the storage process; at most, I would check if the quantity is very significant, and I would verify the storage or the batch date.

No, I would not do this.

I wouldn’t do it. If stored properly and the grease is not that old, it shouldn’t have happened.

If that small amount of oil is enough to pour off then it is not good. This doesn’t give a good impression of the product quality. Also there is chance of oil leakage that reduces the product appearance.

I would not recommend using a separate material. This allows the formulation and homogeneity of the formulation to change. This could cause the grease to potentially not function as prescribed and result in monetary damages. The product should be managed and supplied as a well-formulated, homogeneous system. That being said, if the product is separating, the customer should be aware and the effects in operation should be well described by the supplier as to potential issues.

Not a big concern.

It’s normal, especially in greases formulated with lower viscosity base oils.

Grease in tube should not separate and not be enough to pour off.

Some oil separation is expected depending on the grease thickener and formulation. Many experts suggest that some oil being readily separated is healthy for the performance of the grease in application. Pouring it off is a bad idea; it should be mixed in if possible in order to perform as designed. Excess oil separation is undesirable, and poorly formulated or manufactured grease that bleeds excessively should not be used in important applications.

In my opinion a small bit of oil separation (bleeding) in a grease tube is not a problem. This is after all how grease works. Decanting the oil and then using the grease tube is fine. It depends though how much is meant by “a small amount.” The amount (percentage) of bleeding is an indicator of the quality of grease.
 
I am okay with it, especially for the softer greases, but I know it can create a concern with end-use customers.

If there is an oil separation, the grease is not homogeneous, and there is an improper manufacturing process.

Oil separation should be minimized, but a small amount is not really a cause for concern.
 
Grease needs some oil separation in use to be an effective lubricant. It depends on how small is small.

If there is a minute amount of oil present in a tube of grease, and the grease is not over hardened, this practice is 100% okay.

Not ideal, but it would be a problem if you don’t notice the separation and oil goes into the joint instead of the grease.

Not a big deal if it’s a small amount.

If by small you mean less than 5%-6% of the mass of the grease I’m not worried. I just stir the grease to reincorporate the oil with the thickener and move on. I’m an engineer; I don’t “feel,” I think!

It is ok.

No big deal. The grease we use is over 80% oil and the separation is needed so the oil can do the lubricating.

I’ve never had an issue in field applications using greases with small amounts of separation.

It is normal to see a little oil in a tube of grease, depending on the grease, the time and the storage temperature since its production. It is not a problem to decant or remove the oil, provided that the separation is small (no more than 6% of the total amount of grease in calcium or lithium greases and their complex variants) and to use the grease for its intended application.

Oil separation up to a few percent is not a high cause for concern. If you can decant it, you should since separated oil will bleed out faster from the grease and negatively influence the lubrication. But this needs to be done in a safe way to not cause negative environmental impacts.

I view it as normal, not unusual.

I do not worry about a little bit of oil separation in grease because there is much more oil in grease than there is thickener. A small amount of separation is almost the norm.

It doesn’t matter; it’s normal.

Even a small amount of oil loss from oil separation should be cause for concern of the grease.
Yes 36%
No 64%
Based on an informal poll sent to 15,000 TLT readers.

I don’t like separation.

The oil content of grease is much higher than the solid content, so a small amount of oil separation has little effect on the performance of the grease.

This is bad practice. By removing the oil, you are affecting the ratio of oil and thickener and effectively impacting the grease performance.

Small oil separation would be a concern, but I would probably use it. I would not use it if I had to pour oil out of the tube.

I consider a small amount of oil separation in a grease tube to be a normal phenomenon, as long as it remains within acceptable limits according to product specifications (e.g., ASTM D1742). This slight bleed often indicates the physical stability of the formulation during storage. However, when the amount is such that it can be poured off, it is no longer a desirable condition. That level of separation suggests an incompatibility between the thickener and the base oil, or a deficiency in mechanical stability, which can affect consistency and retention in the lubrication points. In such cases, I would not use the tube without first verifying whether the grease regains a homogeneous texture when mixed again, or if the separation reappears quickly after application.

I would question the thickener/oil coupling. To have separation with only environmental stress would raise questions for me on the performance under actual work. Is the soap reversible? What would my relubrication interval need to be to ensure sufficient oil available to do the work? I would not pour it off. I would try and work it back in.

Q.2. Describe the outcome that a piece of equipment had after you decanted oil separation from a tube of grease and used the decanted tube of grease in service. You may also tell a story that you have been told of this situation.

I have not encountered this. I dispose of separated grease.

I once found a tube of grease with a thin layer of oil on top. Someone said it had “gone bad.” I held it to the light; the oil was clear and clean. The grease underneath looked fine. So I poured off the oil, worked the grease a bit and used it to pack a fan bearing. That fan ran smooth, cool and quiet for months. The next inspection showed the grease still healthy, no drying or crusting. I’ve seen it time and again: a little oil separation isn’t failure—it’s the grease relaxing. As long as the oil’s clear and the body’s pliable, it’ll do its job.

I have asked that question many times. I have never had anyone mention any use problems due to it.

I keep my grease stored in a climate-controlled area and keep my inventory at a low level so it is being used within one year. I have not had an instance of grease separation.

I would not do that.

Knowing what I know, if I had to “pour off” any oil from a grease tube I would not use it.

The oil separation is often asked about by the customer but rarely have I heard of them pouring it off.

I have not had such a situation. In my opinion, the remaining grease would have higher thickener, so the stiffness can be higher and the flowability would be reduced.

I haven’t experienced this with tubes. In the instances that have been shared with me, the grease was stored under pressure in a pressure dispenser or the grease tube was beyond its shelf life and stored in an environment hostile to lubricant performance.

Hardening of the applied grease.

There was usually a shorter service interval for the grease.

The only issue we have seen here is when the grease has to be applied through a long run of tubing. We have had the tubing plug off as the grease can separate over the long run and then we will have to pressure through the lines with a high pressure pump to clear the blockage.

Nothing different because if decant was so big, I would not use and find a better tube of grease to use.

No issues with this practice generally. If the separation is excessive, it should be discarded.

I don’t have direct experience with this, but my feeling would be there would be performance loss due to the reduced oil concentration.

This happens with cheap grease found in hardware and commodity stores. I have used it out of necessity on tractor steering, and the grease dried out prematurely, losing the oil to the environment instead of into the application. Afterward, it was not fluid or tacky enough to stay in the application.

If you have decanted any oil separation from the grease you have permanently changed the consistency to a “harder or stiffer” grease, which may make it unacceptable for high speed applications.

The grease, once the oil is separated, cannot be mixed without the proper machinery. The oil separated is scrap, so the only thing to do is use the grease as it is. It will be a little bit dryer and harder.

I have seen it happen. In most cases, I would anticipate that the lubricator does not even notice or take any action. Most likely they will put the tube into the gun and proceed without any reaction as long as it is indeed a “small” amount.

Equipment functioned as was designed.

If oil separation occurs, one should check the technical data referring to the tube of grease and decide from estimates of the separation and technical data whether the tube of grease is safe for use.
Yes 81%
No 19%
Based on an informal poll sent to 15,000 TLT readers.

Oil leaked out of the back of the grease tube when pressure applied.

I never notice a problem related to using a grease with a small amount of oil separation.

I never decant oil that has separated. Oil separation is expected with the type of grease/applications I have dealt before.

I don’t understand why anyone would be worried when a “small amount” is separated. The typical tube of grease is around 25 cubic inches, about 14 fluid ounces, so there’s 20 cubic inches (about 11 ounces) of oil. So a tablespoon of separated oil (and that’s a lot) is less than 5% of the oil in the tube.

I’ve never had or heard of a situation where decanting oil had caused a failure of such equipment.

Such situations may be taken for separate purposes: one for grease, second for oil.

I have been working as a lubrication technician for three decades and have not found any variations in the performance of lubricated equipment after decanting the grease tube in standard lubrication applications with calcium and lithium greases and their complex variants. I always take care to ensure that the amount of oil separated does not exceed 6% of the total amount of grease. For lubricated equipment to function properly, it is more important to control the amount of grease used to start up the machine or the element to be lubricated, as well as the frequency of regreasing and the amount of grease used in each regreasing.

Acted normally, no issues.

I have never had a problem with using a decanted tube of grease.

The outcome of using a decanted tube of grease in equipment service is potential equipment damage and premature failure due to inadequate lubrication. By decanting the separated oil, you remove the essential base oil needed for lubrication, leaving behind a material that is predominantly thickener and has an improper consistency.

I have never experienced or seen this myself, but I was told that the grease might harden due to the oil loss.

The grease was dry more quickly.

In one case, a field technician decided to pour off the separated oil from a tube of complex lithium grease before applying it to an electric motor bearing. Initially, the grease seemed to perform normally; however, after a few weeks, the bearing temperature and noise levels increased noticeably. Subsequent analysis revealed a significant loss of oil content within the grease structure, reducing its ability to form an adequate lubricating film. In other words, the grease had lost its balance between the oil and thickener phases, leading to poor lubrication and premature wear. Since then, this case has served as an example that visible oil separation should not be corrected by decanting, but rather by reviewing storage conditions, batch control or reformulating if the issue is recurrent.

Nothing to tell as I usually look for an alternative lubricant that would not bleed under storage conditions.

Q.3. Describe the quantity of oil separation allowed in a tube of grease for it to be used in service.

1 mL.

2-3 drops.

5 mm or less at the top of the tube.

2%-3%.

If the oil layer is thin, clear and less than about 5% of the tube volume, the grease is fine. Pour off the excess and put it to work. Anything beyond that, or showing discoloration or odor, means it’s past its shelf life.

In my experience, with a properly manufactured grease there is usually very little to no separation. Time in storage can be a big factor. Date the tubes and see where the “pop” becomes too excessive. Proper inventory management is also important: first in, first out (FIFO).

Very minimal. Just a sheen of oil is cause for concern.

I would say approximately 3%.

Very minimal (slight film if any) and depends on the ambient temperatures of the grease storage and/or environment it is used in.

The air gap in the top of a grease cartridge in small, so the visible amount is minimal. I’d be more concerned of the manufacturing date of the grease and whether or not the product is expired.

The separation usually depends on the manufacturer and thickener.

I would say very minimal.

I would not want any; however, less than a milliliter or two would be acceptable.

A small amount of oil bleed is to be expected. There is a reason the grease industry has an oil bleed test and limits.

If <1 %, it is acceptable under normal conditions. If high temperatures are seen oil separation can increase.

Just a few tablespoons.

Teaspoon, but again depends on how old the tube of grease is.

<5% total volume.

A third of an ounce or a medium spoon.

Perhaps a light sheen on the top.

Extremely small.

It should be less than 2%.

That is a guessing game. Personally, I would change suppliers and find another grease!
 
I would think just an eighth of an inch or so to be acceptable.

A light oil film on top.

I work on a maximum of 10% oil by weight of the tube.

By percent I would estimate 2%-4%.

In a good quality grease, no oil at all.

I have not determined an exact number.

1 to 2 grams would be no concern in my opinion, but I have tubes that have been stored properly for years and had no separation.

5% is “safe for use.”

Not much. Maybe 1% (1-2 mm) if the application isn’t critical.

2% of the tube volume.

I deal with drums, not tubes. Oil separation is expected and normal after the drum being in storage. How much separation I allow is something that is negotiated with the grease manufacturer before sourcing.

1%.

I’ve never looked for a standard on what is allowable, but, when opening a new tube, I have never seen as much as a teaspoon or two of oil. (I also know our grease guns are always slowly leaking oil.)

I’d limit it at around a .125” layer on a standard sized grease tube.

The outcome from oil wetted grease or colloids of grease.

In general, a small visible film of oil—just enough to slightly wet the surface or form a few drops—is considered normal and acceptable for use. If the amount is large enough that oil can be poured off or runs freely, the grease should not be used until it’s remixed or requalified.
 
From my point of view, I do not accept more than 6% of the total amount of grease, in tubes stored for long periods of time or in high temperature conditions (storage temperatures between 30°C and 50°C, which can be found in many environments). If the oil content exceeds 6%, in certain applications, especially in bearings operating at high speeds or high temperatures, we may encounter low grease stability and oil loss above the desired value, which would result in poorer bearing lubrication. On the other hand, for low-performance applications, such as leaf spring or vehicle chassis lubrication, I could tolerate up to 12% grease separation in calcium greases without any problem.

<3% by weight is a generic value that can be used as a rule of thumb. However, this is very dependent on the type of application and the frequency of relubrication. Lubricated for life or low frequency relubrication applications set higher demands on the state of the grease. In a loss lubricated application the demand is lower as the grease is frequently replenished.

Oil bleed is normal as it all depends upon the storage condition, temperature, etc.

Less than 2-3 mL.

5%.

A normal amount of grease bleed separation is expected, with small pools of oil collecting within the surface layer of the grease.

3% max.

Although there are no clear standards, why not check whether the consistency of the grease from which the oil has separated is within the standard?

Slight amount.

The quantity of oil separation should be minimal.

A small amount of oil separation is acceptable, as long as it stays within normal limits defined by the manufacturer or ASTM standards. In general, oil loss of no more than 3%-5% according to ASTM D1742 (Oil Separation from Lubricating Grease During Storage) is considered permissible and does not affect product performance in service. If the separated oil accumulates on the surface or can be poured off, the grease should not be used without prior evaluation. This condition indicates possible colloidal instability or a loss of balance between thickener and base oil, which can compromise lubrication and lead to premature bearing or component failure.

A light sweat.

Editor’s Note: Sounding Board is based on an informal poll sent to 15,000 TLT readers. Views expressed are those of the respondents and do not reflect the opinions of the Society of Tribologists and Lubrication Engineers. STLE does not vouch for the technical accuracy of opinions expressed in Sounding Board, nor does inclusion of a comment represent an endorsement of the technology by STLE.