“I Need an Equivalent Oil or Grease” — Why Khash Starts With the Machine, Not the Brand Name

A technical method for data collection, lubricant selection, compatibility testing and controlled changeover

One of the most common requests I receive is:

“Khash, the OEM recommends this oil or grease. Can you give me an equivalent from another brand?”

Many people expect an immediate product name. However, a responsible lubrication engineer should not begin with a cross-reference table. The process must begin with the machine, operating conditions, lubrication system and existing lubricant.

A cross-reference can identify possible candidates, but it cannot confirm that a lubricant is technically suitable, compatible with the lubricant already inside the machine, acceptable to the OEM, or safe to introduce without a controlled changeover.

My principle is simple:

An equivalent lubricant is not a product with a similar name, colour, ISO viscosity grade or NLGI grade. It is a lubricant that can perform the required functions in the specific machine, under the actual operating conditions, without creating an unacceptable compatibility or reliability risk.

I therefore separate every request into four engineering stages:

1. Collect the right information.
2. Select technically qualified alternatives.
3. Test compatibility and transition risks.
4. Implement and monitor a controlled changeover.

Oil and grease must be evaluated separately because they behave differently, are specified differently and require different changeover procedures.

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Part I — Replacing an OEM-Recommended Oil

1. Why “same ISO VG” does not mean “equivalent oil”

Two oils may both be labelled ISO VG 68 and still be fundamentally different.

They may use different:

• Base-oil families
• Viscosity indices
• Antiwear systems
• Extreme-pressure additive systems
• Rust and corrosion inhibitors
• Demulsifiers
• Foam inhibitors
• Detergent and dispersant packages
• Friction modifiers
• Seal-conditioning additives
• Oxidation inhibitors
• Tackifiers or solid lubricants

ISO 3448 establishes an industrial lubricant viscosity classification system. It does not establish that oils within the same ISO viscosity grade have equivalent oxidation life, wear protection, demulsibility, filterability, air release, material compatibility or OEM approval. (ISO)

Therefore:

ISO VG is only one line in the selection process—not the final selection.

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2. The information I collect before recommending an alternative oil

2.1 Confirm the equipment and lubricant function

I first identify exactly what is being lubricated:

• Gearbox
• Hydraulic system
• Steam or gas turbine
• Compressor
• Circulating-oil system
• Journal or thrust bearing
• Rolling bearing
• Vacuum pump
• Refrigeration compressor
• Chain or total-loss system
• Heat-transfer system
• Transformer or electrical equipment
• Engine or mobile equipment

The same viscosity grade may be used in several of these applications, but the required additive chemistry and performance tests can be completely different.

For example, an ISO VG 46 turbine oil, ISO VG 46 hydraulic oil, ISO VG 46 compressor oil and ISO VG 46 industrial gear oil are not automatically interchangeable.

2.2 Obtain the exact OEM requirement

I request:

• Equipment manufacturer
• Equipment model and serial number
• Year of manufacture
• Lubrication manual revision
• Lubricant table from the manual
• Recommended product name
• Required viscosity grade
• Required industry specification
• Required OEM specification
• OEM-approved lubricant list
• Ambient-temperature restrictions
• Oil-change requirements
• Warranty status

I separate the OEM requirement into two categories.

Mandatory requirements may include:

• Required OEM approval
• ISO viscosity grade
• DIN, ISO, AGMA, API or other performance category
• Fire resistance
• Food-grade registration
• Biodegradability
• Electrical properties
• Gas or refrigerant compatibility
• Prohibition of certain additive systems
• Seal-material restrictions

Preferences may include:

• The lubricant brand originally supplied with the machine
• A regional product recommendation
• A commercially preferred supplier
• A product that was available when the manual was written

This distinction is important. Sometimes an OEM names one lubricant as an example but permits any oil meeting the stated specification. In other cases, only formally approved products may be used.

I also distinguish carefully between the following supplier statements:

• OEM approved
• Listed on the OEM approval list
• Meets the OEM specification
• Recommended for applications requiring the specification
• Suitable for use
• Comparable with
• Similar to

These statements do not provide the same level of evidence.

During the warranty period, or for safety-critical machinery, written OEM acceptance may be necessary before using a product that is not formally approved.

2.3 Collect actual operating conditions

The lubricant must be selected for the machine’s real duty, not only its nameplate duty.

I collect:

• Minimum and maximum ambient temperature
• Cold-start temperature
• Normal bulk-oil temperature
• Supply-oil temperature
• Return-oil temperature
• Bearing or gear hot-spot temperature
• Maximum observed operating temperature
• Speed and speed variation
• Load and load variation
• Shock loading
• Start-stop frequency
• Reversing or oscillating operation
• Duty cycle
• Equipment criticality
• Expected operating life
• Current oil consumption
• Leakage history
• Historical failure modes

An oil with excellent high-temperature properties may be too viscous during cold start. Another oil may pump easily but provide insufficient film thickness at the actual operating temperature.

For hydrodynamic bearings, gears and rolling bearings, I evaluate the lubricant’s viscosity at the actual contact temperature, not only its reported viscosity at 40°C.

2.4 Understand the complete lubrication system

I document:

• Total system volume
• Reservoir working volume
• Reservoir shape
• Suction-line arrangement
• Return-line arrangement
• Coolers and heaters
• Filter type and micron rating
• Filter Beta ratio
• Normal filter differential pressure
• Bypass-valve setting
• Pump type
• Operating pressure
• Flow rate
• Accumulators
• Servo valves
• Fine-clearance components
• Centrifuges
• Water-removal systems
• Electrostatic or varnish-removal systems
• Dead legs and low points
• Piping that cannot be drained
• Separate control and lubrication circuits
• Materials used in reservoir coatings, hoses and seals

The system design determines both the required oil performance and the amount of old oil likely to remain during the changeover.

2.5 Identify the current oil—not only the oil shown in the store

I request the exact current product name and supporting documents:

• Product data sheet
• Safety data sheet
• Batch information where available
• ISO viscosity grade
• Base-oil type
• Additive type
• OEM approvals
• Service hours
• Installation date
• Top-up history
• Previous lubricant changes
• Previous flushing method
• Quantity of oil added between changes

A common problem is that the name on the lubrication chart is not necessarily the oil currently inside the machine.

During years of operation, different oils may have been added. A machine may contain a mixture even before the proposed changeover begins.

Therefore, I compare:

• Store records
• CMMS records
• Lubrication tags
• Oil-analysis additive fingerprints
• Operator information
• Purchase history
• Drum and transfer-container identification

2.6 Identify material-compatibility risks

The candidate oil must be reviewed against all wetted materials:

• NBR
• FKM
• EPDM
• Silicone elastomers
• Polyurethane
• Neoprene
• PTFE
• Reservoir paints and coatings
• Adhesives
• Hose materials
• Filter media
• Copper and brass
• Bronze
• Silver-containing components
• White-metal bearings
• Aluminium
• Zinc-containing components

A base-oil change can affect seal swelling, shrinkage, hardness, leakage and coating integrity.

ASTM D4289 provides a method for assessing lubricant interaction with elastomer coupons by measuring changes in volume and hardness after controlled immersion. Where the actual seal compound is known, testing representative material is preferable to relying only on a generic statement such as “compatible with common seals.” (ASTM Store)

2.7 Collect a representative used-oil sample

I strongly prefer to receive a sample from the operating machine—not only a new-oil sample from an unopened drum.

Depending on the application, baseline analysis may include:

• Kinematic viscosity at 40°C and 100°C
• Viscosity index
• Acid number
• Base number where applicable
• Karl Fischer water
• Particle count
• Elemental spectroscopy
• Ferrous density or PQ index
• Analytical ferrography
• FTIR oxidation and contamination
• Insolubles
• Membrane patch inspection
• Demulsibility
• Foaming
• Air release
• Rust protection
• Copper corrosion
• Filterability
• Remaining antioxidant concentration
• Oxidation stability
• Varnish-potential testing

For turbine systems, I may additionally consider:

• Membrane Patch Colorimetry
• RPVOT
• Remaining antioxidant measurement
• Demulsibility
• Air release
• Foam tendency
• Water
• Particle count
• Electrostatic discharge history

For hydraulic systems, filterability and the condition of the existing fluid are especially important.

A new oil may be compatible with another new oil but react poorly with an aged oil containing oxidation products, water, cleaning chemicals or contaminants. Current ASTM practices for both turbine and hydraulic oils specifically recognize that in-service lubricant compatibility must be evaluated separately because ageing and contamination can change the result. (ASTM Store)

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3. How I technically select alternative oils

Once the information is complete, I build a compliance matrix.

Selection Gate 1: Mandatory specification and approval

A candidate is rejected or escalated for OEM review when it does not satisfy a non-negotiable requirement.

I verify:

• Exact viscosity grade
• Application category
• Performance specification
• OEM approval status
• Regulatory requirement
• Food-grade status where required
• Biodegradability where required
• Fire-resistant-fluid category where required
• Gas or refrigerant compatibility
• Electrical or dielectric requirement
• Restrictions relating to metals and elastomers

Selection Gate 2: Viscosity at operating temperature

I compare:

• Kinematic viscosity at 40°C
• Kinematic viscosity at 100°C
• Viscosity index
• Low-temperature viscosity
• Pumpability
• Expected viscosity at the minimum start temperature
• Expected viscosity at the normal and maximum operating temperatures
• Shear stability where viscosity-index improvers are present

Pour point is not a complete measure of cold-start suitability, and flash point is not the maximum continuous operating temperature.

For rolling bearings, gears and journal bearings, the objective is to achieve sufficient operating viscosity and film thickness without creating excessive churning, friction, heat generation or start-up resistance.

Selection Gate 3: Base-oil chemistry

I identify whether the existing and proposed oils are based on:

• Conventional mineral oil
• Highly refined mineral oil
• Hydrocracked base oil
• PAO
• Ester
• PAG
• Oil-soluble PAG
• Silicone
• Phosphate ester
• PFPE
• Vegetable-derived or other biodegradable base stocks

The base-oil family affects:

• Miscibility
• Seal behaviour
• Solvency
• Deposit removal
• Paint compatibility
• Thermal stability
• Oxidation resistance
• Volatility
• Water behaviour
• Lubricity
• Density
• Heat transfer

Even oils from nominally similar base-stock families can be incompatible because of additive interactions.

Selection Gate 4: Additive architecture

I determine what the machine actually requires:

• Rust and oxidation-inhibited oil
• Zinc-containing antiwear oil
• Ashless antiwear oil
• Sulfur-phosphorus EP gear oil
• Micropitting-resistant gear oil
• Detergent or dispersant oil
• Non-detergent circulating oil
• Compounded oil
• Tackified oil
• Friction-modified oil
• Solid-lubricant-containing oil

For example, replacing an R&O turbine oil with a detergent hydraulic oil simply because both products are ISO VG 32 could create serious problems with air release, water separation and deposit behaviour.

Selection Gate 5: Application-specific performance

Different applications require different performance evidence.

Application	Important properties beyond ISO VG
Hydraulic system	Filterability, antiwear performance, air release, foam control, seal compatibility, oxidation stability and water separation
Industrial gearbox	Scuffing protection, micropitting resistance, bearing wear protection, copper compatibility, foam control, demulsibility and shear stability
Turbine system	Oxidation resistance, varnish tendency, air release, foam control, demulsibility, rust protection and filterability
Compressor	Base-oil compatibility with the compressed gas or refrigerant, deposit tendency, volatility, oxidation resistance, seal behaviour and separator compatibility
Circulating-oil system	Rust protection, demulsibility, air release, filterability, oxidation stability and deposit control
Journal or thrust bearing	Operating viscosity, oxidation stability, air release, foam control, cleanliness and material compatibility

A single four-ball result, flash point or oxidation-test value cannot represent total lubricant performance.

Selection Gate 6: Evidence quality

I evaluate the strength of the supporting evidence:

• Formal OEM approval
• Product qualification against an industry specification
• Independent laboratory data
• Supplier laboratory data
• Relevant field experience
• Written technical recommendation
• Product data-sheet comparison
• Marketing claim

Product data-sheet values are useful for screening, but many are typical values rather than guaranteed manufacturing limits.

Selection Gate 7: Classify the proposed alternative

I normally classify a candidate as one of four types:

Direct replacement:
The candidate meets the mandatory requirements, has the required approvals, uses a technically comparable chemistry and presents a low transition risk.

Conditional alternative:
The candidate is technically suitable but requires compatibility testing, OEM clarification, flushing or intensified monitoring.

Engineered upgrade:
The product is intentionally different—for example, moving from mineral oil to PAO or another synthetic technology—to improve temperature capability, oxidation life, energy efficiency or drain interval. It requires a formal engineering justification and changeover plan.

Not recommended:
The candidate fails a mandatory requirement or presents an unacceptable compatibility, material, operational or warranty risk.

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4. Oil compatibility testing before changeover

Compatibility is not the same as equivalence

This distinction is essential.

Two oils may be compatible when mixed but the mixture may still provide inadequate:

• Wear protection
• Load-carrying capability
• Oxidation life
• Demulsibility
• Foam control
• Filterability
• Seal performance

Conversely, two individually excellent oils may react badly when mixed.

ASTM D7752-26 explicitly states that hydraulic-fluid compatibility does not prove equivalent oxidation resistance or wear protection. Its primary protocol evaluates mixtures at 2:98, 10:90 and 50:50 ratios using wet-filterability testing. (ASTM Store)

For turbine oils, ASTM D7155-20(2026) uses a tiered approach covering:

1. Visual compatibility
2. Interfacial properties
3. Physical and chemical properties
4. Specific performance properties

The standard also warns that passing only a visual examination is not an adequate compatibility assessment. (ASTM Store)

My oil compatibility matrix

Where possible, I request testing of:

• New current oil
• New proposed oil
• Representative used oil from the machine
• New-current/new-proposed mixtures
• Used-current/new-proposed mixtures

The blend ratios should represent credible field conditions. These may include:

• A small top-up concentration
• The predicted residual after draining
• A partially completed displacement flush
• A 50:50 worst-case mixture
• A high concentration of the proposed oil containing a small residual of the old oil

The applicable ASTM, ISO or OEM method should take priority where one exists.

Primary compatibility observations

After controlled mixing, conditioning and heat-storage cycles, I inspect for:

• Haze
• Cloudiness
• Sediment
• Flocculation
• Gel formation
• Layering
• Phase separation
• Colour change
• Surface skin
• Filter deposits
• Abnormal odour
• Precipitated additive material

A clear bottle does not prove acceptable compatibility. Some reactions become visible only after heating, cooling, water exposure, ageing or filtration.

Secondary physical and chemical tests

Depending on the application, I compare:

• Viscosity at 40°C and 100°C
• Acid number
• FTIR spectra
• Elemental additive fingerprint
• Insolubles
• Water separation
• Foam tendency and stability
• Air release
• Filterability
• Rust protection
• Copper corrosion
• Elastomer response
• Oxidation performance
• Antiwear or EP performance
• Varnish tendency

Acceptance limits must be defined before the test. The mixture should not be approved merely because it “looks acceptable.”

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5. Selecting the correct oil-changeover method

Method A: Controlled top-up transition

This method should only be considered when:

• The products are demonstrably compatible
• They have the same required application category
• The viscosity grades are suitable
• There is no major base-oil or additive-system change
• The OEM permits mixing or gradual transition
• The machine is not highly sensitive or safety critical

Even then, I define the maximum top-up concentration, sampling frequency and monitoring requirements.

Method B: Drain and refill

This may be suitable when:

• Compatibility is confirmed
• The residual old-oil concentration is acceptable
• The system drains effectively
• The chemistry difference is limited
• Deposits and contamination are under control

Coolers, filter housings, piping low points, cylinders and accumulators must be considered. Draining the reservoir alone does not necessarily remove most of the old oil.

Method C: Displacement flush or repeated drain-and-fill

This is required when:

• The lubricant chemistries differ significantly
• Compatibility results are marginal
• The system retains a high residual volume
• Fine servo valves or filters are present
• The current oil is contaminated or degraded
• A high cleanliness level is required
• The OEM specifies a residual-oil limit

A simplified residual calculation can be useful.

If the fraction of oil remaining after each complete drain is $r$, the theoretical remaining old-oil fraction after $n$ identical drain-and-refill cycles is:$$\text{Remaining old-oil fraction}=r^n$$

For example, if 10% remains after each drain:

• After one cycle: 10%
• After two cycles: 1%
• After three cycles: 0.1%

Real systems may retain more because mixing is imperfect and old oil can remain in dead legs, coolers, bearings, cylinders and low-flow areas.

Method D: Complete cleaning or specialist flushing

This is considered when:

• Base oils are immiscible
• Severe varnish or sludge is present
• A phosphate ester, PAG, silicone or PFPE conversion is involved
• The new lubricant has strong solvency and may release deposits
• Coating compatibility is uncertain
• Safety-critical or high-temperature systems are involved
• The OEM requires complete removal

Chemical cleaners should not be introduced without confirming their compatibility with the new oil, seals, coatings and filtration system.

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6. Correct oil-changeover execution

A controlled oil change should include the following sequence.

Before shutdown

• Approve the management-of-change document.
• Record the machine’s normal temperature, pressure, vibration, flow and filter differential pressure.
• Take a representative baseline oil sample.
• Prepare the required quantity of new oil and flushing oil.
• Prepare new filters, breathers, seals and sampling containers.
• Verify that transfer equipment is clean and dedicated.
• Establish acceptance limits and stop criteria.

During draining and cleaning

• Drain the oil warm where safe and permitted.
• Open designated low-point drains.
• Drain coolers, filters, piping and auxiliary reservoirs.
• Inspect the reservoir floor and magnetic plugs.
• Remove sludge, water and settled debris.
• Avoid lint-producing cleaning materials.
• Replace filters where required.
• Inspect seals, hoses and coatings.
• Confirm that drains and return paths are open.

During flushing

• Use a flushing lubricant approved for the system and final oil.
• Circulate through all normal and auxiliary flow paths.
• Operate valves and actuators where safe to displace trapped oil.
• Monitor filter differential pressure.
• Replace loaded filters as required.
• Sample the flushing fluid.
• Continue until the defined cleanliness, water, viscosity, residual chemistry and visual criteria are achieved.

Filling and commissioning

• Filter the new oil during transfer.
• Use sealed, clean transfer containers.
• Fill to the correct operating level.
• Prime pumps and bleed trapped air.
• Confirm oil flow before applying full load.
• Check for foam, abnormal noise, leakage and unstable pressure.
• Monitor temperature and filter differential pressure closely.
• Inspect the system for released deposits during the first operating period.

Post-change monitoring

A risk-based monitoring schedule may include:

• A sample after initial circulation
• A sample after the first operating shift or first few days
• A sample after several weeks
• A sample after the first significant operating interval
• Return to the normal oil-analysis schedule only after stability is confirmed

The post-change tests should verify:

• Correct viscosity
• Water control
• Particle cleanliness
• Absence of abnormal filter plugging
• Stable additive fingerprint
• Acceptable wear trend
• No unexpected oxidation or deposit formation
• Stable machine temperature, pressure and vibration

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Part II — Replacing an OEM-Recommended Grease

1. Why grease cross-referencing is even more complex

A grease is not simply a thick oil.

Its performance depends on the interaction of:

• Base oil
• Base-oil viscosity
• Thickener
• Thickener concentration
• Additive package
• Solid lubricants
• Mechanical structure
• Oil-release behaviour
• Manufacturing process

Two greases may both be NLGI 2 lithium-complex greases and still behave differently in a bearing.

They may differ in:

• Base-oil viscosity by several times
• Mechanical stability
• Oil bleeding
• Pumpability
• Low-temperature torque
• Water resistance
• Corrosion protection
• EP performance
• High-speed suitability
• Bearing noise
• Seal compatibility
• Relubrication interval

NLGI grade describes consistency through penetration classification. It does not define base-oil viscosity, load capacity, speed suitability or expected grease life.

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2. The information I collect before recommending an alternative grease

2.1 Identify the component exactly

I request:

• Bearing or component manufacturer
• Bearing designation
• Bearing type
• Bore diameter
• Outside diameter
• Bearing width
• Cage type
• Internal clearance
• Open, shielded or sealed design
• Housing type
• Shaft orientation
• Locating or non-locating position
• Number of bearing rows
• Lubrication groove and hole arrangement
• Seal design
• Free internal volume

The recommendation for a high-speed deep-groove ball bearing can be very different from that for a slow, heavily loaded spherical roller bearing.

2.2 Collect speed information

I calculate or review the bearing speed factor:$$n\times d_m$$

where:

• $n$ is rotational speed in revolutions per minute
• $d_m$ is the bearing mean diameter, normally calculated from bore and outside diameter

This is important because high-speed bearings generally require:

• Lower base-oil viscosity
• Suitable grease consistency
• Controlled oil release
• Low internal friction
• Good channeling behaviour
• Low torque
• Carefully controlled grease quantity

A grease selected only because it has a high four-ball weld load may be unsuitable for a high-speed motor bearing.

2.3 Collect load and motion information

I request:

• Radial load
• Axial load
• Combined load
• Shock loading
• Vibration
• Oscillation
• Small-amplitude movement
• Frequent starts and stops
• Reversing motion
• Bearing load ratio where available
• Misalignment
• Potential skidding or sliding
• Fretting exposure

Low-speed, highly loaded or oscillating applications may need a different base-oil viscosity and additive package than a continuously rotating bearing.

2.4 Measure the real temperature

I distinguish among:

• Ambient temperature
• Housing-surface temperature
• Outer-ring temperature
• Estimated inner-ring temperature
• Grease supply-line temperature
• Minimum start-up temperature
• Maximum transient temperature
• Continuous operating temperature

Dropping point should not be treated as the grease’s maximum continuous operating temperature. Grease life, oxidation, oil release and thickener stability normally become limiting factors well before the dropping point is reached.

2.5 Understand contamination and environment

I collect information about:

• Water ingress
• Condensation
• Steam
• Washdown
• Seawater
• Dust
• Cement
• Coal
• Scale
• Process chemicals
• Acids or alkalis
• High humidity
• Vacuum
• Radiation
• Oxygen service
• Food or pharmaceutical contact
• Electrical current
• High vibration

The environment influences thickener selection, corrosion protection, sealing strategy and relubrication frequency.

2.6 Understand the grease-delivery system

I document:

• Manual grease gun or automatic system
• Single-point lubricator
• Single-line or dual-line centralized system
• Injector or divider-block type
• Pump type and pressure
• Grease-line length
• Grease-line internal diameter
• Lowest line temperature
• Metered quantity
• Relief-valve setting
• Feed-point location
• Grease-discharge path
• Purge outlet
• Bearing rotation during relubrication
• Existing blocked or hardened lines

A grease may perform well inside the bearing but fail to reach it through a long centralized line.

2.7 Identify the current grease completely

I request:

• Exact product name
• NLGI grade
• Thickener type
• Base-oil type
• Base-oil viscosity at 40°C and 100°C
• Solid lubricants
• EP and AW additives
• Operating-temperature range
• Relubrication quantity
• Relubrication frequency
• Time in service
• Top-up history
• Grease consumption
• Leakage or purge history

Colour is not a reliable basis for grease identification. Different greases may have the same colour, while the same grease may darken during service.

2.8 Inspect the used grease and failure symptoms

Where possible, I request an actual grease sample and inspect for:

• Excessive softening
• Hardening
• Oil separation
• Dry thickener
• Contamination
• Water
• Metallic particles
• Oxidation
• Colour changes
• Burnt odour
• Mixed-grease appearance

I also ask whether the application shows:

• Rising bearing temperature
• Grease leakage
• Motor-current increase
• High vibration
• Bearing noise
• Frequent relubrication demand
• Grease starvation
• Grease churning
• Blocked relief passages
• Hardened grease in the housing
• Purging from seals
• Central-system high-pressure alarms

These observations often reveal whether the original problem is the grease selection, the amount, the interval, the delivery path or the bearing condition.

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3. How I technically select an alternative grease

Selection Gate 1: Base-oil viscosity and film formation

The base oil provides the lubricating film. The thickener primarily retains and releases that oil.

I therefore compare:

• Base-oil viscosity at 40°C
• Base-oil viscosity at 100°C
• Viscosity-temperature behaviour
• Expected base-oil viscosity at bearing operating temperature
• Bearing speed
• Load
• Contact geometry
• Lubrication regime

A grease with the correct NLGI grade but the wrong base-oil viscosity can produce either starvation and inadequate film or excessive churning and heat.

Selection Gate 2: NLGI consistency

I select consistency according to:

• Bearing retention
• Orientation
• Seal configuration
• Pumpability
• Centralized-system requirements
• Ambient temperature
• Churning risk
• Leakage risk

NLGI 2 is common, but it is not automatically correct for every bearing.

A centralized system operating in a cold environment may require a softer grease, while a vertical or poorly sealed arrangement may need greater retention. The final decision must consider both pumpability and bearing behaviour.

Selection Gate 3: Thickener system

I compare thickener technologies such as:

• Lithium
• Lithium complex
• Calcium
• Calcium sulfonate complex
• Aluminium complex
• Polyurea
• Clay or bentonite
• Barium complex
• Sodium
• Other specialty thickeners

The thickener affects:

• Mechanical stability
• Water resistance
• Oil release
• Pumpability
• High-temperature behaviour
• Compatibility with the existing grease
• Corrosion protection
• Grease life

However, thickener name alone cannot prove compatibility or performance.

Selection Gate 4: Oil release and mechanical stability

A grease must release enough oil to lubricate the contact without bleeding excessively.

I review:

• Oil separation during storage
• Oil separation at elevated temperature
• Prolonged worked penetration
• Roll stability
• Shear stability
• Structural recovery where relevant
• Leakage and channeling behaviour

Excessive hardening may prevent oil release. Excessive softening may cause leakage and loss of grease from the bearing.

Selection Gate 5: Water and corrosion performance

For wet environments, I compare:

• Water washout
• Water spray-off
• Wet roll stability
• Rust protection
• EMCOR performance
• Saltwater performance
• Copper corrosion

Water resistance is not represented by thickener type alone.

Selection Gate 6: Wear and load-carrying performance

Depending on the application, I review:

• Four-ball wear
• Four-ball weld load
• Timken load
• SRV wear or EP performance
• Fretting protection
• False-brinelling resistance
• Bearing-specific test data
• Gear or coupling performance where applicable

A high EP result does not automatically make a grease suitable for a high-speed rolling bearing.

Selection Gate 7: Special application requirements

I verify whether the application requires:

• Low-noise grease
• Electric-motor grease
• High-speed spindle grease
• Food-grade registration
• Biodegradability
• Conductive or electrically insulating behaviour
• Solid lubricants
• Silicone-free formulation
• PFPE chemistry
• Oxygen compatibility
• Radiation resistance
• Vacuum suitability
• Resistance to process chemicals
• Compatibility with automatic lubricators

Modern grease specifications demonstrate why a grease cannot be judged from one or two values. The NLGI HPM framework, for example, evaluates consistency, prolonged working, elastomer response, oxidation, oil separation, water resistance, wear, EP performance and corrosion, with additional performance categories for specific environments. (NLGI)

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4. Correct grease-compatibility testing

Why a compatibility chart is not enough

Grease compatibility charts are useful for preliminary screening, but they are not final approval documents.

Greases with similar thickener types are often compatible, but ASTM D6185 notes that compatibility cannot be predicted with certainty from composition alone. Additive interactions can make even apparently similar greases incompatible. (ASTM Store)

Incompatibility may produce:

• Severe softening
• Hardening
• Excessive oil separation
• Partial thickener collapse
• Complete separation of oil and thickener
• Leakage from the bearing
• Blocked grease lines
• Poor oil release
• Reduced load-carrying performance
• Accelerated bearing failure

ASTM D6185 mixture ratios

ASTM D6185-24 evaluates binary grease mixtures and identifies three useful ratios:

• 50:50
• 10:90
• 90:10

The 50:50 mixture represents a situation in which a new grease is added without effective removal of the old grease. The 10:90 and 90:10 mixtures represent conditions that may occur during purging. Importantly, a 50:50 mixture can pass while a more dilute mixture fails, so testing only one ratio may miss a compatibility problem. (ASTM Store)

Primary ASTM D6185 testing

The primary protocol evaluates:

• Dropping point
• Prolonged 100,000-stroke worked penetration
• Elevated-temperature storage stability through penetration change

The greases should be considered compatible under the practice only when all required mixtures pass the relevant primary tests. (ASTM Store)

Additional application-specific tests

For critical applications, I may add:

• Oil separation
• Roll stability
• Wet roll stability
• Water washout
• Water spray-off
• Rust protection
• Copper corrosion
• Low-temperature torque
• Pumpability
• Grease mobility
• Four-ball wear
• EP performance
• Fretting tests
• Elastomer compatibility
• Bearing test-rig evaluation

Compatibility testing should include both neat greases as references. A mixture result without comparison to the two original products can be misleading.

Where possible, I also evaluate the proposed grease against an actual used-grease sample. Used grease may contain oxidation products, wear debris, water or process contaminants that are not represented by a new-grease-to-new-grease test.

Compatibility does not prove equivalent performance

A mixture may remain mechanically stable but still have:

• An unsuitable base-oil viscosity
• Diluted additives
• Reduced corrosion protection
• Reduced EP performance
• Poorer grease life
• Inadequate water resistance
• Poor pumpability

Therefore, grease selection and grease compatibility are two separate approvals.

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5. Selecting the correct grease-changeover method

Method A: Complete removal and cleaning

This is the preferred method when:

• Compatibility is unknown or unacceptable
• The bearing is highly critical
• The grease chemistries are substantially different
• The old grease contains solids
• PFPE, silicone or another specialty chemistry is involved
• Contamination is present
• The bearing can be safely opened
• The existing grease has hardened
• The discharge route is blocked
• The OEM requires complete cleaning

The bearing and housing should be cleaned using a method acceptable to the component and lubricant manufacturers. The cleaning agent must be completely removed before the new grease is installed.

Method B: Controlled purge conversion

This may be used when:

• Laboratory compatibility is acceptable
• The bearing is relubricatable
• A functional grease outlet exists
• The old grease can be displaced
• The OEM permits purging
• Overgreasing can be controlled
• The bearing can be monitored

The objective is not merely to pump until the colour changes. The objective is to replace the old grease while controlling temperature, pressure, seal damage and churning.

Method C: Direct top-up

Direct top-up is normally appropriate only when:

• The same approved grease is being used
• The product identity is certain
• The grease is clean
• The quantity and interval are correct

Introducing a different grease as a routine top-up without compatibility evaluation is not a controlled changeover.

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6. Correct grease-changeover application steps

Before the change

• Record baseline bearing temperature.
• Record vibration and noise.
• Record motor current where relevant.
• Inspect seals and grease outlets.
• Confirm that the relief path is open.
• Verify the correct grease point.
• Clean the grease nipple and surrounding area.
• Use a dedicated, correctly labelled grease gun.
• Confirm the calculated quantity and temporary purge quantity.
• Establish stop limits for temperature, pressure and vibration.

During a purge conversion

Where the OEM procedure permits:

• Add the new grease slowly.
• Rotate the bearing where safe and operationally permitted.
• Allow time for grease movement through the bearing.
• Observe the discharge grease.
• Monitor bearing temperature.
• Monitor grease-gun or centralized-system pressure.
• Stop if pressure rises abnormally.
• Do not force grease through blocked passages.
• Do not damage seals by excessive pressure.
• Do not assume that visible new grease at the outlet means no old grease remains elsewhere in the housing.

A temporary increase in relubrication frequency may be necessary during the transition, but the quantity and interval must be controlled to avoid overgreasing.

Centralized lubrication systems

For centralized systems, I evaluate the lines separately from the bearing.

The changeover plan may require:

• Draining the reservoir
• Cleaning the pump reservoir
• Removing hardened grease
• Flushing main and branch lines
• Confirming injector or divider-block movement
• Verifying pressure at the furthest point
• Checking grease mobility at the minimum ambient temperature
• Confirming the metered output
• Purging each point individually
• Inspecting pressure alarms and relief valves

Purging a bearing does not necessarily flush a long grease line.

After the change

I monitor:

• Bearing temperature
• Vibration
• Noise
• Motor current
• Seal leakage
• Grease purging
• Grease consumption
• Central-system pressure
• Injector or divider operation
• Grease condition at the outlet

After the transition is stable, I optimize the normal grease quantity and relubrication interval. The temporary changeover quantity should not automatically become the permanent lubrication quantity.

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The Final Recommendation Package I Provide

When I recommend an alternative oil or grease, the responsible deliverable should contain more than a product name.

My technical recommendation normally includes:

1. Application data sheet

A record of the machine, operating conditions, environment, lubrication system and current lubricant.

2. Compliance matrix

A side-by-side comparison of:

• OEM requirements
• Current product
• Proposed product
• Mandatory approvals
• Important physical properties
• Relevant performance tests
• Identified gaps

3. Recommendation classification

The product is identified as:

• Direct replacement
• Conditional alternative
• Engineered upgrade
• Not recommended

4. Compatibility-test plan

This defines:

• Samples required
• Blend ratios
• Conditioning procedure
• Tests
• Acceptance criteria
• Laboratory responsibility
• Required OEM or supplier review

5. Changeover procedure

This defines:

• Top-up, drain-and-fill, purge, flush or complete cleaning
• Expected residual concentration
• Filters and consumables
• Sampling points
• Commissioning procedure
• Stop criteria
• Waste handling

6. Field-trial plan

For a conditional alternative or upgrade, I prefer a controlled trial on a suitable asset with:

• Baseline operating data
• Defined trial duration
• Temperature and vibration limits
• Oil- or grease-analysis schedule
• Inspection requirements
• Success criteria
• Failure and rollback criteria

7. Documentation update

After approval, the plant should update:

• Lubrication charts
• CMMS records
• Machine tags
• Storage labels
• Transfer equipment
• Grease-gun identification
• Training documents
• Procurement specifications
• Oil-analysis reference data

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My Final Principle

When someone asks me for an equivalent lubricant, I do not see only two product names.

I see:

• A machine
• A lubrication regime
• A required film thickness
• A chemical system
• An operating environment
• A maintenance process
• A compatibility risk
• A controlled changeover
• A reliability result that must be verified

The right alternative can reduce cost, improve availability, simplify inventory and extend equipment life. The wrong alternative—or the right lubricant introduced using the wrong changeover procedure—can cause filter blockage, leakage, deposit formation, lubricant starvation, overheating, wear and premature failure.

Cross-referencing identifies candidates. Engineering selects the lubricant. Laboratory testing manages compatibility. Correct application completes the change. Condition monitoring proves the result.

Khashayar Hajiahmad
MLE, CLS, MLA III, MLT II, VIM, VPR
Lubrication & Reliability Consultant | Noria Approved Instructor