Motor Bearing Lubrication: A Case Study on Temperature and Vibration Issues
Introduction
Motor bearings are critical for smooth operation, but lubrication problems can cause unexpected issues. Recently, several engineers asked about motor bearing lubrication, and one case stood out.
To help you learn from real-world experience, I’m sharing this story—without revealing specific names or locations to respect privacy.
The Case: What Happened of Motor Bearing Lubrication?
In mid-January 2025, a factory in northern China performed maintenance on a 250 kW motor. The motor uses double deep groove ball bearings, model 6316/C3, and was originally lubricated with a well-known international brand’s No. 2 grease. During maintenance, workers added about 10 grams of grease.
After lubrication, the motor bearings started showing problems:
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Vibration increased.
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Temperature rose from around 25°C to 39°C over nearly two hours.
Just as the team prepared to shut down the motor, the temperature and vibration began to drop, and the motor returned to normal. No shutdown was needed.
Past Incidents:
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November 2024: A similar issue lasted about 3.5 hours.
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September 2024: Another incident, but milder, lasted 40 minutes.
The engineers wanted to know: What caused this?
Analyzing the Problem of Motor Bearing Lubrication
Since the issue started after lubrication, let’s focus on what could have gone wrong during grease replenishment.
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Was the Grease Mixed Incorrectly?
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What to check: Did they mix different grease brands or types? Mixing incompatible greases can cause chemical reactions, ruining lubrication.
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In this case: No mixing occurred. The issue also resolved itself without intervention, which wouldn’t happen if grease incompatibility was the problem.
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Was Too Much Grease Added?
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How much is right?: For bearing 6316, the recommended grease amount is calculated using:
Grease quantity (grams)=0.005×D×B
Where D is the outer diameter and B is the width.
- For 6316, this is 33 grams. They added only 10 grams—less than needed. So, over-lubrication isn’t the issue.
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Was the Grease Added Properly?
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What to look for: Contamination or poor application can cause problems.
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In this case: The process seemed fine—grease was brought in, injected, and done. Plus, the motor recovered on its own, suggesting no lasting damage or contamination.
So, what was the real problem?
The Key Clue: Temperature Differences
Here’s where things get interesting. The incident happened in mid-January in northern China—a cold region. The motor took about 3 hours to return to normal. This pattern matched previous incidents: November (cold) had a similar 3.5-hour issue, while September (warmer) had a shorter, milder problem.
The Insight: The grease wasn’t pre-warmed before adding it to the motor. In cold weather, grease is thicker. Adding cold, thick grease to a warm motor can cause temporary issues.
Why Does Temperature of Motor Bearing Lubrication Matter?
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Grease behavior: Grease gets thicker when cold and thinner when warm.
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Inside the motor, the grease is warm (same as the bearing temperature).
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In cold weather, the new grease is much colder and thicker.
When cold grease is added:
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It doesn’t mix well with the warm grease.
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It may clump or resist spreading, causing temporary stirring and poor lubrication.
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This leads to increased vibration and temperature.
But after a few hours, the cold grease warms up, mixes properly, and the problem disappears—if no damage was done.
Conclusion: Pre-Warm Your Grease
In cold climates, especially in winter, it’s crucial to pre-warm the grease before adding it to the motor. This means letting the grease sit indoors for a while to reach a similar temperature as the motor.
Why? It prevents the temporary mismatch in grease consistency, avoiding unnecessary stress on the bearings.