How to Choose Bearing Grease: NLGI, Temperature, Compatibility

Searches for “bearing grease” and “how to choose grease” usually expect one “best” brand. There isn’t one. There is a correct match for speed, temperature, load, and delivery method — plus a hard rule: do not mix incompatible greases.

What grease is made of

Base oil builds the film. Thickener holds oil in the cavity. Additives cover EP, corrosion, water resistance. The bearing needs the oil film first; thickener is delivery, not “more is better.”

NLGI grade

NLGI	Typical use
1	Low temperature, centralized systems, oscillating motion
2	Default for most industrial bearings
3	Large bearings, vertical shafts, strong vibration, high ambient heat

Thicker is not safer. Too stiff at high speed → churning and heat; too soft → runs out and leaves dry contact.

Temperature and base-oil viscosity

• Normal shop to ~+80…+100 °C — mineral lithium NLGI 2 often works.
• Above ~+120…+150 °C — lithium complex, polyurea, specialty HT greases; shorter intervals.
• Below −20…−30 °C — synthetic, low start torque, often NLGI 1–2.
• High DN — relatively lower base-oil viscosity or you get churning.

If a motor shield is “always hot” after greasing, check volume and consistency before blaming the brand — why motor bearings overheat.

Thickener and environment

Lithium / lithium complex — industrial default. Calcium complexes — better water wash-off resistance. Polyurea — common in motors and HT (check compatibility!). Dusty mining/cement — seals and nipple cleanliness matter more than a “miracle grease.”

Compatibility trap

Mixing incompatible thickeners can soften or harden the product, kill oil bleed, and create dry spots. Rules: one approved grade per point; changeover needs purge/flush per OEM; color is not compatibility. Details: grease incompatibility.

Five-minute selection

1. OEM datasheet / plant map first.
2. Note speed, size, load, temperature, moisture/dust, shaft orientation.
3. Pick NLGI (usually 2) and suitable base-oil viscosity.
4. Check seal and in-service grease compatibility.
5. Lock the grade in the map so the next shift does not “improve” it with another tub.

Right grease ≠ right dose

Even perfect grease kills bearings when over-applied. Formulas are ceilings; condition changes shift to shift — condition-based lubrication. LUBExpert does not pick the grade for you; it stops extra pumps once the film is restored.

KEG TRK helps plants in Kazakhstan build grade + dose + control programs. Consultation.