Grease Thickener Compatibility

Mixing greases with incompatible thickeners can cause dramatic changes in consistency, leading to bearing damage or failure. Understanding compatibility is essential when changing lubricants or when multiple greases may come into contact.

Understanding Compatibility Categories

Compatible

Mixing causes minimal change to grease properties. The combined grease typically maintains adequate performance.

Borderline

Mixing may cause some property changes. Test the mixture before use in critical applications, or purge one grease before adding the other.

Incompatible

Mixing causes significant property changes—typically severe softening or hardening. Do not mix; complete purge required when changing.

Consequences of Mixing Incompatible Greases

Softening

Grease loses consistency and may leak from bearing or fail to stay in place. Dropping point may be reduced.

Hardening

Grease becomes too stiff to lubricate properly. May channel away from contact surfaces.

Oil Separation

Base oil separates from thickener structure, leaving dry thickener and free oil.

Additive Interference

Even “compatible” greases may have incompatible additive packages, reducing performance.

Changeover Procedure

When switching to a different grease type:

If compatible: Apply new grease until old grease is purged
If borderline: Increase purging frequency initially
If incompatible: Disassemble if possible, clean bearings, repack with new grease
For sealed bearings: Replace bearing rather than attempting to change grease

Compatibility Testing

If compatibility is unknown:

Mix greases in equal parts
Store at elevated temperature (70-100°C) for 24 hours
Check for consistency change, oil separation, or other abnormalities
Compare dropping point to original greases

Field Mixing Considerations

In real-world maintenance, some mixing is often unavoidable. To minimize risk:

Standardize on one grease type where possible
Label grease guns and fittings
Document which grease is used where
Monitor bearings after grease changes

Compatible Combinations

Thickener 1	Thickener 2	Compatibility	Notes
Lithium	Lithium Complex	Compatible	Most common combination
Lithium	Calcium	Borderline	Test before mixing
Lithium Complex	Calcium Complex	Borderline	Test before mixing
Calcium	Calcium Complex	Compatible	Generally safe
Calcium Sulfonate	Lithium Complex	Compatible	Generally safe
Aluminum Complex	Lithium Complex	Borderline	Test before mixing
Polyurea	Polyurea	Compatible	Same thickener type

Incompatible Combinations

Thickener 1	Thickener 2	Result of Mixing	Risk Level
Lithium	Polyurea	Softening, reduced dropping point	High
Lithium Complex	Polyurea	Severe softening	High
Calcium	Polyurea	Unpredictable consistency	High
Calcium Sulfonate	Polyurea	Hardening or softening	High
Aluminum Complex	Polyurea	Softening	High
Clay (Bentonite)	Most soaps	Softening, separation	High
Silica	Most soaps	Unpredictable results	Moderate
Barium Complex	Most others	Generally incompatible	High

Notes

- Compatible means mixing typically does not cause significant property change
- Borderline means performance may be affected—test in non-critical application first
- Incompatible greases may soften dramatically, harden, or separate
- Even 'compatible' greases should not be mixed if avoidable—unknown additive interactions
- When changing grease types, purge old grease completely when possible