Grease incompatibility: why you must not mix greases in a bearing

The maintenance store often holds three "almost identical" tubs. The fitter tops up with whichever is nearest. Weeks later the bearing is noisy, hot or failed — and the "bad grease" gets the blame, when the real cause is incompatibility.

In industrial practice the question "can I mix greases" almost always has the same answer: no, unless compatibility has been proven.

What actually clashes

Incompatibility is usually driven not by colour or the brand on the label but by the thickener type and the additive package. Mixing can cause:

• sharp softening (grease runs out and the bearing goes dry);
• hardening / clumping (channels blocked, grease never reaches the contact);
• degraded oil bleed — the film in the rolling zone disappears;
• loss of water resistance and anti-wear properties.

Visually the mixture can look "fine" for the first few hours. The problems appear under load and temperature.

A simplified practical matrix

Exact tables come from the grease manufacturers — check against them. General store rules:

Situation	Action
Same brand, same specification	Usually acceptable
An "equivalent" with no compatibility sheet	Treat as incompatible
Lithium ↔ calcium / complex / polyurea / bentonite	High risk — do not mix
Food-grade H1 ↔ ordinary industrial	Prohibited by site procedure
Unknown grease in the assembly	Do not top up by guesswork

Colour (blue / red / green) does not equal compatibility.

How to change brand safely

1. Record the current brand on the lubrication point map.
2. Obtain a compatibility sheet from the supplier of the new grease relative to the old one.
3. If compatibility is not confirmed:
   • strip and clean the assembly per the OEM procedure, or
   • perform a controlled purge with a large volume of the new grease through the drain (where the design allows), recording it in the log.
4. Rename the point in the CMMS: new brand, changeover date, responsible person.
5. Remove the "similar" tubs from the store shelf next to the route — physically separate them.

Half of all "grease changeover" incidents are not sabotage but a missing note on the point map.

The link to dose and over-greasing

Incompatibility and over-greasing reinforce each other. A thickened mixture in the channel prompts the fitter to "pump some more", pressure rises and the seal is pushed out. The symptoms resemble the consequences of over-greasing, but the root cause lies in chemistry, not only in grams.

Correct material selection — choosing a grease. Correct technique — how to grease bearings.

How a monitoring programme catches the problem before the failure

After a brand change, or when a "foreign" tub is suspected, it helps to compare the acoustic friction level before and after the service against the point history. A sharp unexplained rise in the signal at the same load is a reason to stop the route and check whether an incompatible mixture got in.

LUBExpert keeps the history per asset and stops you from blindly finishing off the bearing, but it does not replace store discipline. First one approved brand per point — then the precise dose.

KEG TRK helps build the lubrication programme: point map, brands, training personnel in acoustic control. Get in touch.