Standards explainer compiled by cBallast. 3-page PDF; the full content is on this page.
Compiled by
cBallast
Subject
Lubricating greases
Document type
Standards explainer
Reference
2026 edition
Issued
2026-10-04
Pages
3
Format
Web page and PDF
Which grease thickeners can be mixed and which must never meet, the NLGI consistency scale, base-oil compatibility, and the safe purge procedure when changing grease type in a bearing.
Thickener compatibility matrix
Li
Li-complex
Ca-sulfonate
Polyurea
Clay (bentone)
Al-complex
Lithium
—
C
C
I
I
I
Lithium-complex
C
—
C
B
I
C
Calcium-sulfonate
C
C
—
B
I
B
Polyurea
I
B
B
—
I
I
Clay (bentone)
I
I
I
I
—
I
Aluminium-complex
I
C
B
I
I
—
C = generally compatible · B = borderline, test or purge thoroughly · I = incompatible: the mixture softens or hardens and loses its oil. Matrices differ slightly between producers because additive packages matter as much as thickeners — when in doubt, treat the pair as incompatible. Base oils add a second layer: mineral and PAO mix; silicone and PFPE oils mix with nothing else.
Compatible pair (C): relubricate at half the usual interval twice, so the old grease is progressively displaced.
Borderline or incompatible (B/I): purge — grease through the bearing until fresh grease exits clean, or strip and wash the bearing and housing with solvent, dry, and repack 30–50 % free volume. Mark the housing with the new grease type.
Polyurea-filled electric-motor bearings deserve special care: most general lithium EP greases are incompatible with them — purge fully or replace the sealed bearing.
High-viscosity and special greases (e.g. SKF LGEM 2 for slow heavily-loaded bearings) follow the same matrix by their thickener family — the designation letter rarely says which, so check the datasheet line "thickener". Relubrication quantities and intervals per bearing size are in the bearing maker's tables; bearing dimensions themselves are in the bearing chart.
Frequently asked questions
Can I mix lithium and polyurea grease?
No — lithium and conventional polyurea thickeners are incompatible: the blend softens and bleeds oil. Purge the bearing completely before changing between them.
What does NLGI 2 mean?
The standard consistency grade for rolling-bearing grease: worked penetration 265–295 tenths of a millimetre — firm enough to stay in the bearing, soft enough to flow to the contacts.
Are lithium and lithium-complex greases compatible?
Yes, generally — they share the thickener chemistry; follow the shortened-interval top-up routine so the old fill is displaced.
How do I change to an incompatible grease?
Purge the bearing until only fresh grease exits, or dismantle, wash and dry the bearing and housing, then repack 30–50 % of the free volume with the new grease and label the point.
Do base oils affect compatibility too?
Yes: mineral and PAO base oils mix, but silicone and PFPE-based greases are incompatible with everything outside their own family regardless of thickener.