Greases / 6 min
Grease Equivalent Selection: NLGI, Thickener and Base Oil Compatibility
Grease isn't simply thickened oil — it's a complex chemical structure. Because of this, seeking an equivalent or alternative brand of grease carries far higher risk than with liquid industrial oils. Two greases having the same color or brand perception doesn't mean they can be substituted for one another.
Published by: Rotek Technical Content Team
Content is published based on manufacturer technical documentation and equipment requirements as the basis for final selection. This is general guidance and does not replace equipment-specific manufacturer approval.
Review our editorial guidelinesTable of Contents
- - Why Grease Equivalence Logic Is Different
- - Matching NLGI Consistency Classes
- - Thickener (Soap) Structure Compatibility
- - The Importance of Base Oil Type and Viscosity
- - Technical Matching and OEM Approval
Why Grease Equivalence Logic Is Different
In liquid oils, only viscosity and additive chemistry apply. In greases, a thickener (soap), which acts like a sponge, is added to this system. When the soap structures of two different brands' greases contact one another, incompatibility can occur, causing the grease to suddenly liquefy and abandon the bearing.
Matching NLGI Consistency Classes
The NLGI number indicating a grease's hardness (for example NLGI 2 or NLGI 3) is the first property to check. Central lubrication systems use more fluid greases like NLGI 0 or 1, while hand-pumped bearings typically use NLGI 2. The NLGI number of the equivalent product must exactly match the current one.
Thickener (Soap) Structure Compatibility
A grease's structure is formed by soaps such as lithium, calcium, polyurea or aluminum complex. For example, a lithium complex grease cannot be mixed with a polyurea grease. When looking for an equivalent, it's critical to identify your current grease's soap type and find an alternative with the same or fully compatible thickener structure.
The Importance of Base Oil Type and Viscosity
The base oil's viscosity inside the grease determines its load capacity and speed factor. A high-speed electric motor bearing requires a grease with a thin base oil viscosity (e.g. 100 cSt), while a heavily loaded furnace bearing requires a grease with a thick base oil (e.g. 460 cSt). This viscosity equivalence must always be sought during equivalent transitions.
Technical Matching and OEM Approval
Brand A's lithium complex may not have exactly the same chemical balance as Brand B's — so a direct brand equivalence cannot be claimed between the two products. For trouble-free operation, the machine manufacturer's (OEM) specifications must be followed before switching, and final suitability requires OEM approval. Send us your current product's brand, code and label information so our technical team can evaluate the safest match.
Frequently Asked Questions
Does lithium complex grease mix with polyurea grease?
No, it doesn't. These two thickeners are chemically incompatible and turn to sludge or suddenly liquefy when mixed.
Can NLGI 3 be used instead of NLGI 2 grease?
Generally not. NLGI 3 is a stiffer grease and can clog central lubrication systems or cause overheating in high-speed bearings.
Is grease color a criterion in equivalent selection?
No, it isn't. Color is only added via dye and isn't a technical standard determining the grease's quality, properties or application area.
Is checking only the dropping point sufficient for high-temperature greases?
It's not sufficient. Alongside dropping point, how quickly the base oil inside the grease evaporates at high temperature, and its oxidation life, must also be matched.