Industrial bearing grease should be selected from the bearing’s real duty: load, speed, operating temperature, contamination exposure, sealing arrangement and relubrication method. NLGI grade is important for handling and delivery, but it does not by itself define oil-film capability, high-temperature life or compatibility with the grease already in service.

Start with the bearing duty and lubrication arrangement

Before comparing grease products, identify the bearing and the conditions that act on it. The bearing designation, size, arrangement and housing design affect both the lubricant requirement and the quantity that can be safely retained. Use the OEM or bearing manufacturer’s documentation where it specifies a grease family, initial fill, relubrication quantity or speed limit.

Collect the following information before ordering grease:

  • Bearing designation, internal clearance where relevant, and whether the bearing is open, shielded or sealed.
  • Radial and axial load, including shock loading, start-stop duty and periods at low speed.
  • Shaft speed, direction of rotation and expected operating temperature at the bearing location.
  • Housing orientation, available free volume, grease relief path and seal arrangement.
  • Ambient conditions, including washdown, humidity, outdoor exposure, dust, process chemicals and temperature cycling.
  • Current grease product, its technical data sheet, relubrication route and observed failure history.
  • Delivery method: manual gun, single-point automatic lubricator or centralized lubrication system.

This information matters because grease selection is a system decision rather than a product-label decision. SKF’s grease-selection process, for example, considers operating conditions, bearing type and arrangement, size, temperature, speed, interfaces, sealing and mounting conditions together. SKF’s selection guidance is a useful framework, but the applicable limits still depend on the exact bearing and machine arrangement.

If site records show overheating, leakage, blocked grease lines or repeated bearing damage, do not assume the grease is the root cause. Misalignment, excessive preload, electrical damage, ingress through failed seals, vibration and incorrect fill quantity can produce similar symptoms. Review the failure evidence before changing lubricant.

Match base-oil viscosity and additives to load and speed

The oil released from grease does the primary lubricating work at the rolling contacts. The grease thickener holds that oil in place and releases it under service conditions. For this reason, base-oil viscosity at operating temperature is usually more relevant to film formation than the grease’s NLGI consistency grade.

Higher load, shock loading or slow rotation can require a grease with a base oil viscous enough to maintain an adequate separating film. Higher speed can shift the balance in the other direction: excessive viscosity or excessive grease volume may raise churning losses and bearing temperature. A grease that is appropriate for a slowly rotating loaded bearing may therefore be unsuitable for a high-speed electric motor or spindle.

For electric-motor bearings, Mobil’s technical guidance states that oil viscosity should suit load and speed at operating temperature, while noting that the motor builder may provide a specific recommendation. That principle is useful beyond motors, but it is not a universal viscosity specification for every bearing application. Mobil’s electric-motor bearing lubrication guide should be read as application-specific context rather than as a substitute for bearing manufacturer guidance.

Do not confuse base-oil viscosity with NLGI grade

NLGI grade describes grease consistency, or relative firmness. It influences pumpability, channeling behaviour and whether a grease can be delivered through lines and metering devices. It does not tell you the base-oil viscosity, thickener chemistry, additive system or temperature capability.

Two NLGI 2 greases may have substantially different base oils, thickeners and intended duties. One may be formulated for general rolling bearings, while another may be designed for water exposure, high load or higher-temperature service. Compare the candidate product’s technical data sheet for at least:

  • Base-oil type and viscosity.
  • Thickener type.
  • NLGI grade.
  • Published operating-temperature range and stated limitations.
  • Corrosion protection, water resistance or washout information where relevant.
  • Any stated compatibility, material or application restrictions.

Extreme-pressure (EP) or anti-wear (AW) additives may be appropriate for some loaded bearing duties. SKF recommends verifying the lubrication condition and considering EP/AW additives in its selection process. However, additive selection should remain application-specific. Certain additives can affect corrosion behaviour, fatigue performance or material compatibility in particular bearing designs. Follow the bearing and grease manufacturers’ published guidance where it identifies restrictions or approved lubricant families.

Check temperature, thickener and consistency together

Temperature changes several grease properties at once. As temperature rises, base-oil viscosity falls, oxidation tends to increase and the thickener system can lose its ability to retain or release oil as intended. At low ambient temperature, grease may become difficult to pump, especially through long centralized-lubrication lines.

SKF states that standard greases commonly have a practical upper temperature limit of 100 °C at the hottest bearing ring; above that condition, special greases or automatic or centralized greasing may be needed because grease life may otherwise be too short. This is a general selection warning, not a design limit for every grease, bearing or housing. The exact product data sheet and bearing manufacturer’s limits take precedence. SKF’s guidance also advises checking the lubricant’s influence on operating temperature and speed as speed approaches recommended limits.

The grease thickener is part of this temperature decision. Lithium complex, polyurea, calcium sulfonate complex and other thickener systems can have different temperature behaviour, water resistance, mechanical stability and compatibility characteristics. No thickener type is automatically correct for every industrial bearing.

For a centralized system, confirm that the proposed grease can move through the actual installation. Obtain the lubrication-system supplier’s permitted grease consistency range, line-length limits, minimum ambient-temperature guidance, pump capability and metering-device requirements. A grease may be appropriate at the bearing but unsuitable for the pump, progressive divider or distribution lines used to supply it.

Account for water, dust, chemicals and bearing sealing

Environmental exposure can dominate grease choice. Water ingress may promote corrosion, reduce grease consistency or wash lubricant away. Fine dust and process solids can turn grease into an abrasive contaminant carrier. Chemical exposure can affect both grease and seal materials.

Begin with the source and path of contamination. Inspect seal condition, shaft surface quality, housing joints, grease-fitting condition, breather arrangement and the route by which washdown water or dust can enter. Changing to a grease with better water resistance may help in a documented wet-duty application, but it will not compensate for a damaged seal or an open contamination path.

Review the candidate grease manufacturer’s documentation for claims related to water resistance, corrosion protection or chemical exposure. Treat those claims as product-specific, and confirm applicability to the actual concentration, temperature and contact duration. Also check the seal manufacturer’s guidance for the installed elastomer or other seal material. A grease can be suitable for the rolling elements yet unsuitable for a particular seal material or operating environment.

Where a bearing is regularly exposed to contamination, review whether relubrication is intended to replenish lubricant, purge contaminants or both. Purging requires a defined exit path. If expelled grease cannot leave the housing safely, adding more grease can increase churning, leakage and temperature instead of improving cleanliness.

Do not mix greases without a compatibility review

Do not assume two greases can be mixed because they have the same colour, NLGI grade, brand or a broadly similar application label. Compatibility depends on the interacting thickener systems, base oils, additive packages, mixing ratio and service conditions.

Grease compatibility charts can be useful screening tools. For example, Chesterton publishes a grease compatibility quick reference. A chart result does not demonstrate that a specific mixture will perform acceptably in a particular bearing. It cannot establish the effects of residual grease quantity, high temperature, high speed, water ingress or additive interactions in your service.

This caution is especially important for high-speed, high-temperature, precision, sealed-for-life and critical-service bearings. ASTM’s F2489 guide recommends evaluating replacement grease before use in precision-bearing applications. That recommendation should not be expanded into a universal test requirement for all industrial bearings, but it illustrates why a grease change needs more than a visual comparison.

For a planned conversion, obtain guidance from the outgoing and incoming grease manufacturers and from the bearing or machine OEM where available. Review:

  1. Thickener type, base-oil type and base-oil viscosity of both products.
  2. Additive differences and known restrictions for the bearing application.
  3. Expected residual quantity of the old grease.
  4. Required purge, cleaning or disassembly procedure.
  5. Relubrication quantity and monitoring steps after conversion.

If compatibility remains uncertain, do not treat a chart as approval. Use manufacturer guidance and a controlled change plan appropriate to the equipment’s criticality.

Set fill quantity and relubrication method before ordering

A suitable grease can still fail in service if the housing is overfilled, underfilled or relubricated at an unsuitable interval. Initial fill and ongoing relubrication are separate decisions. They depend on bearing type, size, speed, housing free volume, orientation, seal arrangement and whether excess grease can escape.

Timken’s Grease Lubrication Tool Help Guide separates grease selection, initial grease fill and relubrication quantity and frequency. That separation is useful in maintenance planning: a selected grease does not supply the correct fill volume or interval by itself.

Set the following before purchasing or changing grease:

  • The approved grease product and product revision, supported by its current technical data sheet.
  • Initial fill quantity or housing fill condition from OEM or bearing manufacturer guidance.
  • Relubrication quantity and interval for the actual duty.
  • Delivery method and the lubrication-system limits for the chosen consistency.
  • Condition of fittings, lines, injectors, relief points and collection arrangements.
  • The intended monitoring method, such as documented temperature trend, leakage observation, ultrasonic route, vibration programme or grease-consumption record.

Do not apply a generic relubrication interval across different machines simply because they use the same grease. Bearing speed, temperature, contamination and housing design can change the required interval substantially.

Before manual lubrication or work on an automatic system, follow site procedures for isolation, lockout or tagout, guarding, hot surfaces and pressurized grease lines. Do not assume that greasing while equipment is running is safe or permitted. Use the OEM’s specific instructions and the site’s approved maintenance procedure.

Verify the selection with a short bearing-grease review

Use this review before approving a purchase order, a grease conversion or a preventive-maintenance route:

  • Confirm the exact bearing designation, arrangement, seals and machine duty.
  • Record actual load, speed, bearing temperature and environmental exposure where data is available.
  • Compare base-oil viscosity, thickener, NLGI grade, temperature range and additive information from the candidate grease data sheet.
  • Confirm pumpability and dispensing suitability for the manual, single-point or centralized system.
  • Review compatibility with residual grease and document the conversion procedure if changing products.
  • Set initial fill, relubrication quantity, interval and relief or purge provisions from product-specific guidance.
  • Define escalation criteria using OEM, bearing manufacturer or lubricant supplier limits rather than invented temperature, vibration or service-life thresholds.

Is NLGI 2 grease suitable for every industrial bearing?

No. NLGI 2 is a common consistency grade, but it does not establish base-oil viscosity, thickener chemistry, additive package, temperature capability or suitability for a specific lubrication system. Confirm the product against the bearing duty and manufacturer guidance.

Can you mix lithium-complex and polyurea bearing grease?

Do not assume they are compatible. A compatibility reference can screen the combination, but the exact products, residual grease, temperature, speed and bearing criticality still require review. Obtain guidance from the grease manufacturers and follow the OEM’s conversion instructions.

How do load and speed affect industrial bearing grease selection?

Load and speed influence the base-oil viscosity needed at operating temperature and the risk of churning or heat generation. Higher load may require stronger film formation or an appropriate additive system, while higher speed can make viscosity, grease volume and operating temperature more restrictive.

How often should an industrial bearing be relubricated?

Use the interval and quantity for the exact bearing, housing, speed, temperature, contamination level and grease method. Manufacturer tools and published guidance can provide a starting point, but site conditions and condition-monitoring records should determine whether the plan remains suitable.

Choose industrial bearing grease only after the bearing duty, environment and delivery method are defined. Where bearing manufacturer guidance, lubricant manufacturer guidance and site practice conflict—or where the application is outside published limits—escalate the decision to the bearing or lubricant manufacturer before changing products or intervals.