Quick Answer: For most industrial bearings, the default is an NLGI #2 lithium-complex EP grease. Choose the grade by speed — NLGI #1–2 for higher speeds, #2 for general duty, #3 for slow and hot service — and the thickener by duty: polyurea for electric motors and sealed-for-life bearings, lithium complex for general industrial, calcium sulfonate for wet and corrosive sites. Fill only 30–50% of the free space, and never mix thickener families without a purge.
Putting this into practice? See our grease pump range — OEM-compatible hardware, full specifications, fast quoting.
Bearing failures blamed on “bad grease” are usually bad matching: the right chemistry in the wrong grade, or the right grade with the wrong base-oil viscosity for the speed. This guide maps bearing grease types and grades to the three variables that actually decide the choice — speed, load, and environment.
Bearing Grease Types: Thickener Families Compared
The thickener is the sponge that holds the oil — it controls water resistance, temperature ceiling, mechanical stability, and compatibility:
| Thickener | Dropping Point | Water Resistance | Best Bearing Use | Compatibility Warning |
|---|---|---|---|---|
| Lithium | ~190°C | Good | General-purpose, light-to-medium duty | Mixes with lithium complex; not polyurea |
| Lithium complex | ~260°C | Good | The industrial default: motors, pumps, fans, conveyors | Widest compatibility of any family |
| Polyurea | ~250°C | Good | Electric motor bearings, sealed-for-life, long-life applications | Incompatible with most soap greases — purge before switching |
| Calcium sulfonate | ~300°C | Excellent | Wet, washdown, marine, and corrosive environments | Check chart; generally good with lithium |
| Clay (bentonite) | Non-melting | Fair | High-temperature ovens, kilns (slow speeds only) | Poor pumpability; not for centralized systems |
Two rules save more bearings than any brand choice: polyurea for motor bearings (it resists oxidation through long service life — which is why most motor builders fill with it at the factory), and calcium sulfonate wherever water lives. For sliding-dominated joints rather than rolling bearings, see our molybdenum grease guide — moly helps pins and bushings but adds nothing to a high-speed rolling bearing.
NLGI Grades: Choose by Speed First
NLGI grade is consistency — how stiff the grease is. For bearings, speed is the primary selector:
| NLGI Grade | Consistency | Bearing Application |
|---|---|---|
| #0 / #1 | Soft to very soft | Cold climates, centralized systems, some high-speed bearings |
| #2 | Medium (peanut butter) | The default for ~80% of industrial bearings |
| #3 | Stiff | Slow speeds, higher temperatures, vertical shafts where grease must stay put |
The physics: at high speed, stiff grease channels and churns — the bearing runs hot and the grease oxidizes early. At low speed under load, soft grease squeezes out of the contact zone. When in doubt at normal speeds and temperatures, NLGI #2 is the answer.
Base Oil Viscosity: The DN Rule
Bearing speed is expressed as DN (bore in mm × RPM). Match base-oil viscosity to it:
| Speed (DN) | Base Oil Viscosity (40°C) | Typical Service |
|---|---|---|
| Low DN (<100,000) | ISO VG 220–460 | Slow, heavily loaded bearings, crushers, kilns |
| Medium DN (100k–500k) | ISO VG 100–220 | General industrial motors, pumps, gearboxes |
| High DN (>500,000) | ISO VG 32–100 | High-speed spindles, machine-tool bearings |
Most fleet EP2 greases sit at ISO VG 150–220 — the workable middle. The classic mistake is using a heavy VG 460 grease in a fast motor bearing: the bearing runs hot from churning, and the fix is a lighter base oil, not more grease.
Fill Quantity and Relubrication
- Initial fill: 30–50% of free space. High-speed bearings go to the lower end (~30%); slow, dirty, or wet applications may fill 50–75% of the housing for the sealing effect. A packed-full bearing churns, overheats, and blows seals.
- Relubrication interval depends on speed, size, type, temperature, and contamination — from hours at extreme speed to a year in cool, clean service. Our bearing grease calculator computes quantity and interval from bore, speed, temperature, and load.
- Quantity per relube matters as much as interval — small, regular amounts purge contaminants; large rare shots overheat the bearing. If starvation is already suspected, the warning signs are in our bearing grease starvation guide.
Mixing Greases in Bearings
Thickener incompatibility is the silent killer: polyurea mixed into lithium complex can soften the blend until it leaks out, or harden it until it channels. Rules: one grease per bearing; when changing families, purge by relubricating at shortened intervals until the old grease is displaced (or clean the bearing at the next teardown); when the thickener is unknown, treat it as incompatible.
Choosing the grease is half the job — it still has to reach the lube point. The complete grease pump guide covers pump types, pressure ratios, and selection by NLGI grade; or browse the grease pump range for pail, drum, and automated options.
Frequently Asked Questions
What is the best grease for ball bearings?
For most industrial ball bearings at normal speeds: an NLGI #2 lithium-complex EP grease with ISO VG 100–220 base oil. Electric motor bearings do best on polyurea NLGI #2; high-speed spindles need softer grades and lighter base oil; slow heavy bearings want VG 220–460. The application table above maps each case.
What NLGI grade should I use for high-speed bearings?
NLGI #1–2 with a light base oil (ISO VG 32–100). The goal is minimal churning: softer grease and lower viscosity both reduce heat. Fill only about 30% of free space at high speed — overfilling is the most common high-speed lubrication error.
Is polyurea or lithium grease better for electric motors?
Polyurea is the motor-industry favorite for its oxidation resistance and long sealed-for-life capability — most premium motor greases are polyurea NLGI #2. Lithium complex is an acceptable alternative in many motor applications and is more forgiving on compatibility. Never mix the two families in the same bearing.
How full should I pack a bearing with grease?
30–50% of the bearing’s free space for general duty; ~30% for high speed; up to 50–75% of the housing for slow, contaminated, or wet service where the grease mass also seals. A completely packed bearing overheats and can fail seals.
Can I mix two different bearing greases?
Only within compatible thickener families — and even then, expect some performance change. Polyurea with lithium or lithium complex is the classic incompatibility. When switching families, purge the old grease with shortened relubrication intervals or clean the bearing at teardown.
Need Help Specifying Bearing Grease — or the System to Deliver It?
IsoHiTech supplies industrial greases, automatic greasers for bearings, and complete centralized lubrication systems. Tell us your bearing list and conditions and our engineers will match grease and delivery as one spec.
