How to Prevent Greased Bearings from Overheating

Should all greased bearings be fitted with a vent (spring-loaded or other)?

Noria Overheatedbearing
Noria Corporation

Article originally published on

The issue of overheating is related to fluid friction, which is a result of fluid churning. This is a secondary effect of overfilling the cavity at the time of relubrication. Installing a relief vent port can help in this situation, but this would be only addressing the symptom rather than the cause.

Two issues need to be addressed. First is the matter of relubrication practices based on tribal knowledge. While the old-school guidelines can sometimes be correct, the evidence here is that something is not quite right. You need to calculate the volume and the frequency based on the bearing type, size, speed and operating environmental factors.

Second, you must consider the lubricant selection for the application.

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