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Motor Bearing Grease: How to Choose and How Often to Regrease

Release Date ：2026-09-15

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Bearing failures account for over 40% of all electric motor failures, and more than half of those are lubrication-related - wrong grease, over-greasing, under-greasing, or simply waiting too long between regreasing. This guide covers grease selection, regreasing intervals, correct fill volume, and the most common mistakes, so you can extend bearing life to its design value.

SHANGDIAN motor bearing grease

1. Select Grease by Three Metrics, Not Just Brand

Consistency (NLGI grade). Most motor bearings use NLGI 2. Medium-speed heavy-duty applications use grade 3; high-speed light-duty use grade 1. Higher numbers mean firmer grease; too soft and it leaks out.

Dropping point. Must be at least 20C above the maximum bearing operating temperature. Standard lithium grease drops around 180C, suitable for bearing temperatures up to ~120C. For hotter environments use complex lithium or polyurea grease.

Base oil type and viscosity. Mineral oil is fine for normal duty; synthetic oils (PAO, ester) handle higher temperatures and last longer, but cost more. Match viscosity to speed: lower viscosity for high speed, higher for slow heavy loads.

2. Common Motor Bearing Greases Compared

Type	Temp range	Characteristics	Best for
Standard lithium	-20 to 120C	Good value, water resistant	General-purpose LV motors, moderate running hours
Complex lithium	-30 to 150C	High temp, good mechanical stability	Continuous-duty main motors, warm environments
Polyurea	-30 to 180C	High temp, antioxidant, long life	Hot environments, sealed bearings, maintenance-free motors
Synthetic oil-based	-40 to 200C	Wide temp range, long life, premium price	Extreme temperatures, precision equipment, critical stations

3. How Often to Regrease? Three Factors Decide

There is no universal "every three months" rule. The interval depends on:

Running hours: For 24/7 continuous duty with NLGI 2 lithium grease, regrease every 2000-3000 hours. For motors running only a few hours a day, extend to 6-12 months.
Speed and load: Higher speed and heavier load consume grease faster. 2-pole motors (3000 rpm) need more frequent regreasing than 6-pole (1000 rpm).
Ambient temperature and contamination: Above 40C, or in dusty/wet environments, shorten the interval by 30-50%.

The most reliable approach is a lubrication log per motor: record date and quantity of each regreasing, then fine-tune the interval based on bearing temperature and vibration trends.

4. How Much Grease? Over-Greasing Does Harm

Many people assume more grease is better. It is not. Fill the bearing housing to 1/2 to 2/3 of its free volume: 1/2 for high-speed (3000 rpm) motors, 2/3 for medium and low speed.

Too much grease causes churning heat, accelerated oxidation, higher bearing temperature, leakage, and even seal damage. When regreasing, add a small amount at a time and rotate the shaft by hand to distribute it evenly.

5. Three Most Common Mistakes

Mixing grease types: Mixing lithium and polyurea can cause soap-base reactions that soften and leak the grease. When switching type, clean out all old grease completely.
Using expired or degraded grease: Once opened, shelf life shortens. If it shows oil separation, hardening, or discoloration, discard it.
Only topping up, never replacing: Old oxidized grease and carbon deposits build up and block the bearing. Do a full clean and repack at least once a year.

SHANGDIAN (Shanghai Electric Motor Factory) low-voltage induction motors are factory-filled with matched lubricant, and the nameplate or manual specifies the recommended grease type and regreasing interval. If your motors run in high-temperature, dusty, or continuous heavy-duty conditions, contact us for a tailored lubrication plan and explosion-proof motor selection advice.