Executive Summary
While grease thickener and base oil viscosity are both important qualities for an effective grease, readers have mixed opinions on which is truly the most critical. The variety of opinions suggests that the answer likely depends on the application. Applications that require the use of a grease are broad, including those that require fill-for-life or where lubricant leakage is unacceptable.

Q.1. Greases can be very unique, and it is hard to have one grease that fits all applications. So, in all of your grease encounters that you have had in the past, overall, what was more important for the application, the type of grease thickener or the base oil’s viscosity? Why?

Both. They both play a role to match the application.

Base oil viscosity. I think that was a bigger determining factor in lubrication performance.

Base oil viscosity is always first to ensure adequate film thickness based on speed, temperature and load. Often greases of different thickener types can work in a given application.

Reaction with water or emulsified metalworking fluids.

Thickener as it is responsible for most of the critical parameters that are important for application.

Base oil viscosity is much more important to carry load based on application.

They are both very important depending on the application and operating conditions. High speed, low speed, high load, light load, high temp, low temp, wet conditions, dry conditions—the list goes on.

Both are equally important. Having the right base oil viscosity is the same consideration as for fluid lubricants. Having the right thickener and consistency is important for aspects like thermal operating range, pumpability, water resistance, etc. Don’t forget base oil type—mineral or synthetic. Same as for fluid lubes. 

Base oil viscosity. A change in the base oil viscosity can change a grease from a semi-fluid to a semi-solid.

They are both of equal performance. Thickener and base oil need to work together. Use the wrong base oil for the application and the quality of the thickener does not matter. The opposite is also true.

Thickener type is more important to meet specific (or demanding) performance requirements. 
 
Neither. The value of the proper grease is that it does the job of preventing wear and corrosion. In my opinion the most important quality is the overall performance, and that’s a combined function of the thickener, base oil and additives.

For a very long time, the general opinion was that base oil viscosity dictated performance for grease. That has been dispelled. There has been much work done showing that the base oil actually has very little to do with performance. The thickener and the surface active agents play a greater role than thought in the past. Flowability, shock load, wear and pressure protection can all be achieved through thickeners and some additives.

Type of grease thickener.

Both are very important.

Base oil viscosity. Ultimately it’s the base oil that does the lubrication.

Base oil viscosity. Operating temperature can allow for proper oil film thickness and dictate whether or not your grease is going to get where it is needed.

Both are important, with base oil’s viscosity being the most important one as it determines the film thickness. 

Grease thickener is more important than viscosity because the thickener is selected early in a project, or the manufacturer may only make certain types of grease. Viscosity can be fine-tuned later and has less impact on the potential performance of the grease than its thickener type.

The thickener, especially in high temp applications. Greases that melt will dissolve the thickener making the lubrication be only with an oil, not an oil and thickener as there will be no grease left. Same applies for cold temperatures. With the wrong thickener for the application, the thickener can harden up leading to lubricant starvation and/or catastrophic failure.

Both are important, application has significant influence on these. In the field, it does seem to ultimately come down to thickener for compatibility, followed by grade and oil viscosity.

The base oil’s viscosity is more important. The base oil is the one that provides adequate film thickness to carry load of the lubricated system and eventually prevents metal-to-metal contact from happening. Also, a suitable viscosity of the base oil is able to flow properly and carry additives to lubricate the metal parts when needed.

The type of thickener. The thickener introduces the performance characteristics needed to lubricate the application.

Always a combination—need oil viscosity based on load and speed. Need thickener depending on running environment at the bearing. We also have to be mindful of specific applications related to chemicals, extreme heat and non-bearing lube needs.

The base oil viscosity is the dominant factor when choosing a grease. Thickener choice is important in specific applications. Additionally, thickeners are often used as a marketing tool, which can confuse the compatibility issue.

They are both critically important. If the viscosity is too low or too high bearings will overheat and the grease will fail. If the thickener is not compatible the grease mixture can soften and run out leading to failure.

Base oil viscosity is always the most important component in a grease! The oil is what is doing the lubricating and protecting the surfaces from wear.

The additives.
 
Grease thickener, because it largely decides the property of the greases.

Base oil viscosity because the process conditions require specific base oil viscosity. Also in some cases the type of soap is important.

Base oil. Oil performance has a great influence on durability.

The application is most important.

Both are equally important. Proper thickener wrong base oil viscosity can result in starvation or overheating. Wrong thickener proper base oil viscosity can also cause those too.

Both are important, as they both contribute to the success of the product. For a bicycle, what is more important, the wheels or the handlebars? Both are needed!

Grease is a design element of complex nature. The application decides which properties are necessary to fulfill the expected performance of the component/equipment. However, to decide which is the most important I would prefer to have the option of different thickeners and additives than choosing the viscosity of the base oil. This would give you the opportunity to serve a lot of different tribological systems. 

Grease thickener—compatibility.

Base oil viscosity for sure. This will be the relevant parameter for the elastohydrodynamic lubrication (EHL) film.

Grease thickener, as it governs durability across time and temperature.

Thickener would be the more important choice. Thickeners can very quickly break down if used in the wrong application, which will result in immediate oil loss, which can cause immediate equipment issues. Using the wrong oil viscosity may cause issues, but not as quickly, which will allow you time to address any issues related to incorrect viscosity.

The base oil viscosity, because oil viscosity is what really lubricates, what really prevents the surfaces contact.

When comparing a non-melt grease and its base oil viscosity, is it more important that the grease stays intact, allowing for lubrication, or that its base oil viscosity is correct?
A grease that will maintain its composition. 37%
It should be somewhere in between. 38%
The base oil viscosity is more important. 25%
Based on an informal poll sent to 15,000 TLT readers.
 
Viscosity of the base is a critical component, but the thickener can make or break the application, especially considering compatibility, if the customer can purge or not.

The grease thickener is more important because: 1.) It is responsible for delivering the lubricant to the application. Wrong thickener or wrong consistency can result in poor lubrication. 2.) Thickener influences the grease temperature range from cold to hot. 3.) Thickener can deliver additive-like properties or enhance properties such as antiwear (AW) and extreme pressure (EP) and rust protection. 4.) Thickener is responsible for water resistance.

I will say both the grease thickener and the base oil’s viscosity are all important. This is because each has its own role to play. The thickener brings about the purpose and the application of the grease while, without the base oil, the grease cannot be formed or produced.

Grease thickener because of compatibility with prior grease.
 
Base oil chemistry is very important to fit applications. That is probably more important than base oil viscosity or thickener type.
 
Energy saving performance.
 
Of course, the type of grease thickener matters because compatibility, pumpability and mechanical stability are critical for the best performance.

Thickener. Compatibility. Water resistance. 

The base oil viscosity.

There is a lot to the equation in selecting the proper grease. Base oil viscosity is a good place to start since viscosity is critical for proper lubrication. The base oil type often plays a part in selecting the proper viscosity with consideration given to ambient and operating temperature. Operating temperature is also a consideration when selecting the thickener type. Other factors in selecting thickener type include resistance to water ingression, potential contamination with a product in the production line where the grease is applied, rolling or sliding load and frequency of relubrication. 

When comparing a highly water spray off/washout resistant grease and its base oil viscosity, is it more important that the grease stays intact, allowing for lubrication, or that its base oil viscosity is correct?
A grease that will maintain its composition. 60%
It should be somewhere in between. 31%
The base oil viscosity is more important. 9%
Based on an informal poll sent to 15,000 TLT readers.
 
You will need to consider both thickener and base oil viscosity based on the application. Different types of thickener deliver different performance, and the oil film thickness is critical for providing the necessary protection.

It needs to be a balancing act. The type of grease thickener sets the foundation for the grease’s performance, while the base oil’s viscosity fine-tunes its lubricating properties and operating range. By carefully selecting both components, you can create a grease that meets the specific demands of your application.

Both, because they interact with each other.

The importance of the type of thickener or the viscosity of the lubricant determines the application of the lubricant. These parameters have a complex influence on the friction and wear of the contact pair.

Both the thickener type and the base oil viscosity are important for selecting the correct grease for the application. They impart different properties, and both required for effective lubrication.

Both grease thickeners and base oils are important. If you understand the thickeners and their chemical/physical interaction with base oils/additives, you could design excellent greases. In general, the higher the oil viscosity, the thicker the lubrication film between two contact surfaces. At the same time, it is also important to provide good performance at low and high temperatures.

The type of grease thickener because of the application temperature. If you choose the wrong type of thickener according to the temperature behavior, your application will fail.

Base oil viscosity.

Although it isn’t a choice, I would say the performance of the thickener is most important. In many applications, you can use alternate thickeners as long as they meet the performance specs.

The more important among those options is, by far, the type of thickener. The base oil’s viscosity is not a relevant factor because it is not common that the OEMs make a recommendation based on it. For us, the lube engineers, viscosity is maybe the most important characteristic of a grease, as it is when we select an oil, and we spread this idea among the users, but the change of concepts takes more time and requires other voices like the OEMs one.

Type of grease thickener—gives the temperature range and water resistance.

Base oil viscosity—that determines the load capacity of the lubricant and speed.

Both are important. They create a system, and it is better to consider whether there is a possibility of their synergy.

It should be a combination of both to have the proper lubrication. But the most important to me is the thickener.

The base oil viscosity is most important. This controls the lubrication film. The thickener is then the next most important—the delivery system.

The grease thickener was top of mind. The thickener is primarily chosen due to the application and the environment that the grease will be used.

When only the liquid lubricant is left because a thicker can melt away, etc., then, the liquid has no means to stay in place in most grease applications, making the liquid lubricant go away. This, then, leads to lubricant starvation and/or catastrophic failure.

The type of grease thickener because of issues of adhesion to surfaces and its resistance to water washing away.



Q.2. In which applications is it important to use a grease?

Rolling element bearings that do not exceed the speed factor rating.

High load, low speed reciprocating motions.

For applications that are hard to seal or the OEM does not want to design a good seal.

Mostly where oil cannot be retained inside chamber or housing.

Sealed-for-life bearings, for example.

Bearings mostly but any application where the lubricant needs to stay in place like your sunroof.

Any self-contained application.

Everywhere you need to control friction and control undesirable contaminants getting into the system being lubricated.

Rolling bearings and mechanical joints. 
 
Off highway, heavy duty construction/mining.

Many applications benefit from using a grease or are suitable for using a grease as a lubricant.

Large mining equipment.

Any application that a liquid lubricant is not suitable. It is almost always preferable to use a liquid lubricant for cooling, length of lubricant life, etc.

In general, we follow the OEM’s recommendation; if the asset is built for utilizing grease, that is what we do.

Rolling element bearings.

Which statement describes choosing the best grease for an application?
Easy peasy!         11%
I think I’ve got this!         33%
I’m leaving that for the experts! 56%
Based on an informal poll sent to 15,000 TLT readers.

Greases are primarily used in applications that are sealed-for-life, hard to reach or impractical to lubricate with an oil bath. Obvious applications are wheel bearings on vehicles or electric motor bearings. But we also see many sliding applications using greases like rack and pinion gear operations or heaving equipment that would be impossible for oil to stay on the application.

Where the proper viscosity oil will not stay in place.

High temperature applications, extreme water washout environments and I suspect some industrial applications where incidental chemical contact may occur.

Any application that is not sealed or where the seals are likely to leak or fail.

Any application that requires some lubrication between two moving parts.

I use greases for rail track curves.
 
Open bearing.

Lubrication of moving/rotating parts.

Lubricated for life systems do well with greases.

Equipment, e.g., tractors, mower decks, hydraulic buckets.

Anywhere where an oil cannot be used or will leak out. Extreme temperatures as well or if the plant cannot supply air/oil type based on need.

Bearings.

Fill-for-life applications are the go-to choice on when to use a grease.

Start-stop. Low heat transfer. Excluding contaminants and sealing. Sealed-for-life. 

Wherever a grease is called for! 

In so many applications: 1.) gears lubrication, 2.) bearings lubrication, 3.) clearance adjustments, 4.) tracks tensioning and many more.

Wheel bearings.

In applications where it’s not possible to hold liquid lubricants.

Low rotation gear systems.

For machine lubrication in automotive use and in industrial applications.

Inaccessible parts, long relubrication frequency.

No leakage applications.

Those applications in which it is not possible to have an oil bath or an automatic lubrication system.

It is important to use a grease when the stiffness of the product allows it to stay in place. Where sealing is important and where oils will not function due to design or environment.

Whenever it is necessary to reduce the destructive effects of friction forces, a lubricant should be used. The type of lubricant is determined by the application.

Using grease in places that are not suitable for liquid lubrication and may cause design confusion will give better results.

Bearings and gears.

Lower speed areas, applications without sealings.

Grease should be used in lower speed applications that require a lubricant that stays in place.
 
All. Not many that escape grease in some capacity.

Anywhere you cannot use oil bath.

Rolling bearing, guides.

High load, low speed, very long change intervals, low accessibility, bearings.

Grease is primarily oil that stays in place. Applications that do not require heat transfer, filtration or power transfer can use grease.

In applications where you are trying to lubricate moving parts where the lubricant (base oil) has to be kept in place.

In applications where liquid lubricant cannot hang on the surface and drip away.

Having a high washout resistance is important for maritime usage; there are many applications on the deck for corrosion proofing and greasing for low load gear but the need to keep contamination out.

Extreme temperature (high and low temperature) applications, fill-for-life, automotive, aerospace, aviation, wind energy, mining and construction, metal processing (e.g., steel), biodegradable, heavy duty, rail, textile, petrochemical, agriculture, pulp and paper, food and beverage and general industrial manufacturing.

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.