Best Lubricant : How to Select Lubricant for Bearings (2026)

Selecting the correct lubricant for a bearing is one of the most important decisions in machine maintenance. A suitable lubricant can reduce friction, control operating temperature, minimize wear, protect against corrosion and contamination, and help a bearing achieve its expected service life.

However, choosing a lubricant is not as simple as buying a general-purpose grease. The correct selection depends on several operating factors, including bearing type, load, rotational speed, operating temperature, environment, shaft orientation, vibration, contamination, and maintenance requirements. SKF specifically recommends considering these factors when selecting bearing grease.

The two major lubrication choices are grease and oil. Grease is widely used because it remains where it is applied and generally requires simpler equipment. NSK reports that grease is used in approximately 80% of rolling bearings. Oil can be preferable for certain high-speed applications, particularly where continuous circulation and heat removal are required.

This guide explains how to select lubricant for bearings, including grade-wise grease selection, grease-versus-oil comparison, application examples, maintenance practices, common mistakes, and frequently asked questions.

1. Why Correct Bearing Lubricant Selection Matters

A bearing operates under repeated rolling contact. Without adequate lubrication, the contacting surfaces can experience increased friction and wear.

The right lubricant helps create a protective film between surfaces.

Major benefits include:

• Reduced friction
• Lower heat generation
• Reduced surface wear
• Corrosion protection
• Smoother operation
• Reduced maintenance
• Improved reliability
• Longer bearing service life

Incorrect lubricant selection can have the opposite effect. A lubricant that is too thick can create excessive resistance, while one that is too thin may not provide sufficient film strength under the operating conditions.

Therefore, lubricant selection should always begin with the bearing and machine manufacturer’s recommendations.

2. The Basic Bearing Lubricant Selection Process

A simple selection process is:

Bearing Type → Load → Speed → Temperature → Environment → Grease or Oil → Grade/Viscosity → Quantity → Relubrication Interval

Let’s examine each factor.

3. Step 1: Identify the Bearing Type

First determine what type of bearing you are lubricating.

Common types include:

• Deep-groove ball bearings
• Angular-contact ball bearings
• Cylindrical roller bearings
• Tapered roller bearings
• Spherical roller bearings
• Needle roller bearings
• Thrust bearings

Different bearing designs have different contact conditions and lubrication requirements.

For example, a high-speed angular-contact bearing may require a lubricant with very different characteristics from a heavily loaded, slow-speed spherical roller bearing.

Always check the bearing designation and manufacturer’s technical documentation before choosing a lubricant.

4. Step 2: Check the Bearing Load

Load is another major consideration.

Bearings may experience:

• Radial loads
• Axial loads
• Combined loads
• Shock loads
• Continuous loads
• Variable loads

Heavier loads generally require a lubricant capable of maintaining an appropriate protective film under the operating conditions.

Base-oil viscosity is particularly important here. Remember that grease consistency and base-oil viscosity are different properties. NLGI explains that grease consistency is mainly determined by thickener type and concentration, while base-fluid viscosity is a separate characteristic.

General principle

Higher load → carefully evaluate base-oil viscosity and load-carrying capability.

Do not simply choose a higher NLGI number because the machine has a heavy load.

5. Step 3: Check Bearing Speed

Speed has a major influence on lubricant selection.

High-speed bearings can generate significant heat. Excessively viscous grease or too much lubricant can increase churning and friction.

General selection approach

Operating Condition	Possible Lubrication Choice
Low speed	Grease or oil
Moderate speed	Usually grease is practical
High speed	Specialized grease or oil
Very high speed	Often oil or specially formulated grease

For high-speed applications, consult the bearing manufacturer’s speed and lubrication recommendations rather than relying on a generic grease chart.

6. Step 4: Check Operating Temperature

Temperature affects both the bearing and lubricant.

Before selecting a lubricant, determine:

• Normal operating temperature
• Maximum operating temperature
• Minimum startup temperature
• Ambient temperature
• Temperature fluctuations

A grease designed for moderate temperatures may not be appropriate for a continuously hot bearing.

High temperatures can accelerate oxidation and lubricant degradation.

Low temperatures can increase lubricant resistance and make grease difficult to move.

Temperature rule

Select a lubricant whose operating-temperature capability comfortably covers the actual application range.

Do not use the grease’s dropping point alone as the operating-temperature rating.

7. Step 5: Consider the Operating Environment

Environmental conditions can dramatically influence lubricant selection.

Consider whether the bearing is exposed to:

• Water
• Humidity
• Dust
• Dirt
• Chemicals
• Salt
• Outdoor weather
• Wash-down operations
• Vibration

For wet environments, water-resistant grease may be important.

For dusty environments, contamination control and proper sealing become critical.

For chemical environments, the lubricant must be compatible with the chemicals and seals.

8. Step 6: Choose Grease or Oil

After evaluating the operating conditions, decide whether grease or oil is more appropriate.

Grease

Grease is often preferred when:

• Simple lubrication is required
• Lubricant retention is important
• Speeds are moderate
• Cooling requirements are not extreme
• Maintenance simplicity is important

NSK highlights grease’s ease of use, simpler sealing arrangements and reduced leakage/scatter compared with oil.

Oil

Oil may be preferred when:

• High speed is involved
• Continuous cooling is needed
• Oil circulation is available
• Filtration is important
• Heat removal is a major requirement

Oil can circulate through a system and carry heat away from the bearing.

9. Grade-Wise Bearing Grease Selection

The NLGI grade describes grease consistency, or how soft/hard the grease is.

NLGI grades range from very soft 000 through very hard 6. The NLGI classification is based on worked penetration at 25°C.

NLGI Grade Comparison

NLGI Grade	Consistency	General Application Consideration
000	Extremely soft/fluid	Centralized systems, some gear applications
00	Very soft	Semi-fluid lubrication systems
0	Soft	Low-temperature/centralized applications
1	Soft	Pumpability and lower-temperature applications
2	Medium	Common general-purpose bearing grease
3	Firm	Certain bearing and higher-temperature applications
4	Very firm	Specialized applications
5	Very hard	Specialized applications
6	Extremely hard	Highly specialized uses

Important:

NLGI 2 does not mean “best grease.”

It only describes consistency.

NLGI itself explains that grease consistency and base-fluid viscosity are independent properties.

10. NLGI 000, 00 and 0 Grease

These are relatively soft or semi-fluid grades.

They may be appropriate where excellent flow or pumpability is required.

Possible applications:

• Centralized lubrication
• Certain gear systems
• Low-temperature applications
• Systems requiring easy grease movement

They are not automatically suitable for ordinary bearings simply because they flow easily.

11. NLGI 1 Grease

NLGI 1 is softer than NLGI 2.

It can be useful when:

• Pumpability is important
• Lower temperatures are encountered
• A softer grease is specified by the manufacturer
• Centralized lubrication is used

However, application-specific requirements remain more important than the grade number alone.

12. NLGI 2 Grease

NLGI 2 is one of the most widely encountered grades for general-purpose bearing lubrication.

SKF states that a mineral-oil/lithium-thickener grease with NLGI 2 consistency is sufficient for most applications, while also emphasizing that application, bearing type, load, temperature, speed, vibration and contamination must be considered.

Typical applications can include:

• Electric motors
• Fans
• Pumps
• Conveyors
• General industrial machinery

But a suitable NLGI 2 grease still needs the correct base-oil viscosity, thickener, additives and temperature capability.

13. NLGI 3 and Higher Grades

NLGI 3 is firmer than NLGI 2.

Higher grades such as 4, 5 and 6 are increasingly firm and are used for specialized applications.

They should not automatically be selected for bearings simply because they are “thicker.”

A grease that is too stiff can have poor distribution and may increase resistance, depending on the application.

14. Base-Oil Viscosity: An Often-Missed Factor

Many people select grease only by NLGI grade.

That is a mistake.

A grease is primarily composed of lubricating fluid, thickener and additives. NLGI consistency describes the grease’s consistency, but the base-oil viscosity determines an important part of the lubricant film behavior.

For bearing selection, consider:

• Base-oil type
• Base-oil viscosity
• Operating speed
• Load
• Temperature

Simplified principle

Higher speed → often requires lower-viscosity lubricant characteristics.

Higher load → may require higher-viscosity lubricant characteristics.

But actual selection should be made using the bearing manufacturer’s data.

15. Thickener Type Matters

Bearing grease can use different thickener systems.

Common examples include:

• Lithium
• Lithium complex
• Polyurea
• Calcium
• Calcium sulfonate complex
• Aluminum complex
• Other specialty thickeners

The thickener affects properties such as:

• Mechanical stability
• Water resistance
• Temperature performance
• Grease structure
• Compatibility

Two greases with the same NLGI grade can behave very differently because their thickener and base-oil systems differ.

16. Additives in Bearing Grease

Grease may contain additives designed to provide additional performance.

Examples include additives for:

• Anti-wear protection
• Extreme-pressure performance
• Rust protection
• Corrosion resistance
• Oxidation resistance

The correct additive package depends on the application.

Do not assume that a grease containing more additives is automatically better.

17. Grease vs Oil: Detailed Comparison

Factor	Grease	Oil
Physical form	Semi-solid	Liquid
Retention	Very good	Requires containment
Application	Usually simple	Often more complex
High-speed performance	Application dependent	Often advantageous
Heat removal	Limited	Excellent with circulation
Leakage	Generally lower	Higher potential
Filtration	Difficult	Easy
Lubricant monitoring	More difficult	Easier
Maintenance	Generally simpler	Can require equipment
Typical use	Motors, pumps, fans	High-speed/high-temperature systems

NSK notes that grease generally avoids the need for complex pumps and coolers, while oil lubrication can be advantageous where cooling is needed.

18. How to Select Lubricant for Electric Motor Bearings

Electric motors commonly use grease-lubricated bearings.

When selecting grease, check:

1. Motor manufacturer’s recommendation
2. Bearing type
3. Motor speed
4. Operating temperature
5. Grease compatibility
6. Relubrication interval
7. Required NLGI grade

Polyurea and lithium-complex greases are examples of grease families used in different motor applications, but the specific motor manufacturer’s specification should take priority.

19. How to Select Lubricant for Pumps

For pumps, consider:

• Pump speed
• Bearing load
• Temperature
• Water exposure
• Seal arrangement
• Continuous or intermittent operation

Water-resistant grease may be important for applications where water contamination is possible.

20. How to Select Lubricant for Conveyors

Conveyor bearings often operate at moderate speeds but can experience:

• Dust
• Moisture
• Continuous operation
• Variable loads

A suitable grease should therefore provide appropriate contamination resistance, temperature performance and relubrication characteristics.

21. How to Select Lubricant for High-Speed Bearings

High-speed applications require extra attention.

Consider:

• Bearing speed factor
• Base-oil viscosity
• Grease consistency
• Heat generation
• Lubricant quantity
• Cage design
• Operating temperature

Oil may be preferable when continuous heat removal is required.

Do not simply use a “high-temperature grease” and assume it is automatically suitable for high speed.

22. How Much Lubricant Should Be Used?

Correct quantity is just as important as correct lubricant selection.

Under-lubrication

Too little lubricant can cause:

Friction → Heat → Wear → Bearing damage

Over-lubrication

Too much grease can cause:

Churning → Heat → Energy loss → Possible premature failure

The correct quantity should be based on the bearing and equipment manufacturer’s instructions.

23. Lubricant Compatibility

Compatibility is a major issue when changing grease.

NLGI advises that it is best practice not to mix different greases when the compatibility is unknown. It recommends appropriate displacement/purging procedures when changing products and monitoring the bearing for signs of incompatibility.

Possible warning signs include:

• Excessive softening
• Excessive hardening
• Increased temperature
• Grease leakage
• Poor lubrication performance

Always document the lubricant currently being used.

24. Common Mistakes in Lubricant Selection

• Mistake 1: Selecting grease only by NLGI grade
• NLGI grade does not describe the complete lubricant.
• Mistake 2: Choosing the cheapest lubricant
• Low purchase cost can become expensive if bearing life decreases.
• Mistake 3: Ignoring speed
• A lubricant suitable for slow machinery may not be suitable for high-speed bearings.
• Mistake 4: Ignoring temperature
• Always consider actual operating temperature.
• Mistake 5: Mixing greases
• Do not mix products without compatibility information.
• Mistake 6: Over-greasing
• More grease does not mean better lubrication.
• Mistake 7: Ignoring contamination
• Water and dust can rapidly affect bearing and lubricant performance.

25. Practical Lubricant Selection Chart

Application	Common Starting Point	Important Checks
Electric motor	Bearing grease	Speed, temperature, compatibility
Pump	Grease or oil	Water, load, speed
Conveyor	Grease	Dust, water, load
Industrial fan	Grease	Speed, temperature
High-speed spindle	Oil/specialized grease	Speed, cooling
Heavy-load bearing	Specialized grease/oil	Load, viscosity, EP requirements
Wet environment	Water-resistant grease/oil	Corrosion and water resistance
High-temperature machinery	High-temperature grease/oil	Actual operating temperature

This table is a selection starting point, not a substitute for the bearing manufacturer’s specification.

26. Simple Five-Step Method

If you need a quick method for selecting a lubricant, follow these five steps:

• Step 1 : Identify the bearing.
• Step 2 : Measure operating speed and temperature.
• Step 3 : Determine radial/axial load and environmental conditions.
• Step 4 : Choose grease or oil and select the appropriate viscosity/grade.
• Step 5 : Confirm the lubricant against the bearing manufacturer’s recommendation. This approach reduces the risk of selecting a lubricant based solely on marketing claims.

27. Best Practices for Bearing Lubrication

For reliable bearing operation:

• Follow OEM specifications.
• Keep lubricant containers clean.
• Use clean grease guns and tools.
• Avoid mixing incompatible products.
• Apply the correct quantity.
• Maintain proper relubrication intervals.
• Monitor bearing temperature.
• Monitor vibration and noise.
• Check seals for contamination.
• Record lubricant type and maintenance dates.

A documented lubrication program can help prevent avoidable bearing failures.

Conclusion

Selecting the correct lubricant for bearings requires more than choosing a popular grease or an NLGI number. The correct decision should consider bearing type, load, speed, operating temperature, environment, shaft orientation, vibration, contamination and maintenance requirements.

For many general-purpose applications, NLGI 2 grease is a common starting point, and SKF notes that a mineral-oil/lithium-thickener NLGI 2 grease is sufficient for many applications. However, this should not be interpreted as a universal recommendation.

NLGI grade describes grease consistency—not overall lubricant quality. Base-oil viscosity, thickener type, additives, temperature capability and compatibility are equally important.

Grease is often preferred because it is easy to apply, stays in place and generally requires simpler equipment. Oil can be advantageous for high-speed applications or systems where continuous cooling and circulation are important.

The simplest rule is:

Choose the right lubricant for the right bearing, under the right operating conditions, in the right quantity.

Correct lubricant selection can reduce friction, control temperature, minimize wear, improve reliability and help extend bearing service life.

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