Grease Compatibility Chart: Can You Mix Greases?
Topping up a bearing with whatever grease is on the shelf is one of the most common — and most expensive — maintenance mistakes. Mixing two incompatible greases can break down the thickener structure, soften the grease until it runs out of the bearing, or harden it until it starves the bearing entirely. This guide explains what drives compatibility and gives you a practical chart to check before you mix.
What determines grease compatibility?
A grease is base oil held in a thickener (a soap or non-soap structure) plus an additive package. Compatibility is mostly governed by the thickeners: combining two greases with chemically incompatible thickeners can collapse the structure. Base-oil type (mineral vs synthetic such as PAO or PAG) and additives matter too — PAG-based greases in particular are generally incompatible with mineral and PAO greases.
"Compatible" does not mean the mix performs as well as either original grease — it means the blend will not fail dramatically. Even compatible greases should only be mixed when unavoidable.
Grease compatibility chart
Use this as a quick reference for common thickeners. C = generally compatible, B = borderline (test first), I = incompatible. Always confirm with the manufacturer for your specific products.
| Thickener | Lithium | Li Complex | Calcium | Ca Sulphonate | Polyurea | Aluminium Complex |
|---|---|---|---|---|---|---|
| Lithium | C | C | B | B | I | B |
| Lithium Complex | C | C | B | B | I | B |
| Calcium | B | B | C | C | I | B |
| Calcium Sulphonate | B | B | C | C | B | B |
| Polyurea | I | I | I | B | C | B |
| Aluminium Complex | B | B | B | B | B | C |
How to switch greases safely
- Purge, don't top up. Pump fresh grease through the bearing until only the new grease emerges from the relief or seal.
- Increase frequency temporarily. Re-grease at shorter intervals for the first few cycles to flush residual old grease.
- Clean on a full service. For critical equipment, dismantle and wash out the old grease with a suitable solvent before repacking.
- Label the change. Record the new grease on the equipment so the next technician doesn't reintroduce the old type.
Signs of an incompatible mix
Watch for grease that has softened and is leaking from seals, grease that has hardened or crusted at the fitting, rising bearing temperatures, or unusual noise shortly after a grease change. Any of these after switching products points to incompatibility — stop, purge, and standardise on one grease.