Bearing grease compatibility: mixing & changeover
Grease colour does not identify its chemistry or establish compatibility.
On this page9 sections ⌄
What to check
Identify both products
Obtain exact old and new product names, base oils, thickeners and compatibility evidence. A generic thickener matrix is only a screening aid.
Plan an approved changeover
Follow the equipment and lubricant changeover procedure. Mixing can change consistency or oil release; a purge must be compatible with the bearing, seals and waste handling.
Unknown old grease
Do not declare an unknown fill compatible. Record the uncertainty and investigate the original maintenance specification before adding a different grease.
Direct answer
Do not approve a grease mixture from its colour, NLGI grade or thickener name. Identify both complete products, check product-specific compatibility evidence and use a controlled changeover plan. A generic chart cannot verify every formulation sold under one thickener category.
A compatibility decision needs more than one matching label
On a small screen, scroll the table sideways to read every column.
| Observation | What it establishes | Decision |
|---|---|---|
| Both are blue / red / white | A visual description | Not compatibility evidence |
| Both are NLGI 2 | A consistency classification | Not compatibility evidence |
| Both say lithium or polyurea | A broad thickener description | Check exact formulations |
| A chart says compatible | A preliminary screening result | Obtain evidence for the actual pair |
| The actual pair has been tested | Evidence under the test conditions | Confirm those conditions cover the application |
| The old fill is unknown | Product identity is missing | Keep the changeover unverified |
NLGI identifies ASTM D6185 as a method for evaluating grease mixtures. Base fluid, thickener and additives all matter. The test result and the equipment procedure must be considered together; a label match does not replace either.
Before changing the lubricant
- Record the full old and proposed product names, revision and available technical sheets.
- Obtain the approved removal, cleaning or purge procedure for the bearing and housing; do not use a generic volume multiplier.
- Keep clean tools and dedicated or correctly cleaned delivery equipment. Prevent residual grease in a line from becoming an unrecorded third product.
- After the approved change, record the quantity and operating observations. Unexpected hardening, softening, leakage or temperature rise requires investigation, not repeated topping-up.
Can lithium and polyurea greases mix?
There is no single yes/no answer for every product carrying those names. Mobil describes compatibility tests for specified Polyrex products and selected other greases; that statement is not a blanket approval for all polyurea/lithium mixtures. With an unidentified pair, BearingScope records compatibility as unknown.
Reference scope
Manufacturer and technical-institute records reviewed for this page: NLGI technical FAQs; Mobil Polyrex EM / EM 103 product data; Mobil industrial lubricant FAQs; retrieved 2026-10-01 UTC. Values are a dated reference snapshot, not an OEM approval or a substitute for the current technical and safety documents. Original source addresses and retrieval evidence are retained in the private content audit.
Continue with real catalogue data
Preserve the full model, source description and unknown fields when making your shortlist. This reference website does not sell bearings or certify a replacement.
Related questions and tools
Grease vs oil bearing lubrication
Choose the lubrication system before choosing a product name.
Read and apply →Bearing grease viscosity vs NLGI consistency
NLGI grade and base-oil viscosity describe different properties.
Read and apply →Lithium, polyurea & moly bearing greases
A thickener or additive name alone does not define an approved bearing lubricant.
Read and apply →Bearing regreasing quantity & interval
A useful maintenance schedule needs the actual equipment duty, not a universal number of pumps or months.
Read and apply →Sealed-for-life bearings: lubrication & maintenance
Sealed-for-life describes a maintenance concept, not infinite bearing or grease life.
Read and apply →High-temperature bearing lubrication checklist
Check the whole bearing system at temperature: lubricant, seals, cage, clearance and material stability.
Read and apply →Low-temperature bearing grease & starting torque
A bearing that runs acceptably when warm may struggle at a cold start.
Read and apply →High-speed bearing grease, oil-air & oil-mist checks
High-speed selection combines bearing geometry, lubricant supply, heat and preload.
Read and apply →Water exposure & food-grade bearing lubrication
A food-contact category and water resistance answer different questions.
Read and apply →Cleaning bearings before relubrication
Cleaning is a controlled maintenance operation, not a cure for damaged raceways.
Read and apply →Plain, linear & solid-lubricated bearing maintenance
Not every component in a bearing catalogue follows a rolling-bearing greasing procedure.
Read and apply →Wheel-bearing grease: NLGI ratings, types & product comparison
Choose wheel-bearing grease from the hub specification and service conditions, not its colour or the word 'premium'. Compare documented automotive and marine examples, then check the exact assembly before use.
Read and apply →Reference basis & data limits
Manufacturer terminology is retained in the product records. Technical reference basis: JTEKT Basic Bearing Knowledge (boundary dimensions, tolerance classes and lubrication); NSK Bearing ABCs (lubrication, designations and clearance); NTN technical FAQs (closure codes and component interchange); SKF rolling-bearing selection and maintenance references.
Selection workflows and catalogue grouping are BearingScope editorial aids. Verify the current drawing and application requirements before using a candidate. Missing database information is not converted into an assumed match.