Guide
Pump Lubrication
Proper lubrication is essential for bearing life. Learn about grease vs oil lubrication, relubrication intervals, common mistakes, and how to keep pump bearings running smoothly.
6 min readUpdated July 2026
Grease vs Oil
- Grease: Most common for smaller pump bearings. Easy to apply, stays in place, seals out contaminants. But cannot dissipate heat as well as oil. Over-greasing is a common problem.
- Oil: Better for high-speed or high-temperature applications. Oil bath, splash, or circulating oil systems. Provides better heat dissipation and can be filtered. Requires oil seals to prevent leakage.
- Oil mist: A thin film of oil is misted into the bearing housing. Provides constant lubrication and positive pressure that excludes contaminants. Used in large or critical pump installations.
Relubrication Intervals
| Bearing Type | Operating Condition | Relubrication Interval |
|---|---|---|
| Greased ball bearing | Normal temp, clean environment | 6 to 12 months |
| Greased ball bearing | High temp or contamination | 1 to 3 months |
| Oil bath | Normal | Change oil annually |
| Oil bath | High temp or contamination | Change oil every 3 to 6 months |
| Circulating oil | Normal | Change oil annually, filter continuously |
Over-greasing kills bearings
Adding too much grease to a bearing housing causes the bearing to run hot. The grease is churned, generating heat, and the excess pressure can blow out seals. Only fill the bearing housing about one-third to one-half full of grease. Leave room for the grease to expand.
Common Lubrication Mistakes
- Over-greasing: Pumping grease until it comes out the seal. This overfills the housing, causes overheating, and blows seals. Use a measured amount per the manufacturer's spec.
- Mixing incompatible greases: Different grease types (lithium, polyurea, calcium) can be incompatible. Mixing them can cause the grease to soften and leak out. Always know what grease is already in the bearing, or clean it out before adding new.
- Wrong oil viscosity: Too low viscosity: insufficient film, bearing wear. Too high viscosity: drag, heat generation, high starting torque. Use the manufacturer's recommended viscosity for the operating temperature.
- Ignoring oil condition: Oil degrades over time. It oxidises, accumulates water, and picks up wear particles. Test oil condition quarterly for critical pumps. Change when degraded.
- Not cleaning grease fittings: Pumping grease through a dirty fitting injects contaminants into the bearing. Always wipe the fitting clean before greasing.
Best Practices
- Use the manufacturer's recommended lubricant grade and quantity.
- Clean grease fittings before applying grease.
- Use a grease gun with a calibrated output so you know how much grease you are adding.
- For oil-lubricated bearings, check the oil level weekly. Maintain at the correct level on the sight glass.
- Replace oil when it becomes dark, milky (water contamination), or gritty.
- For critical pumps, consider oil analysis to detect bearing wear before failure.
- Keep lubricant containers sealed and clean. Store in a dry, cool location.
Tip: If a bearing runs hot after greasing, it is likely over-greased. Open the drain plug and let the excess grease escape while the pump runs. Once the temperature stabilises, close the drain and you are done.