Twenty minutes after a motor is relubricated, its bearing temperature begins to climb. Before anyone adds more grease, the team needs to determine whether the rise is stabilizing or continuing.
A brief rise can occur while fresh grease redistributes. A temperature that keeps climbing may point to excess grease, a restricted outlet, the wrong product, changed operating conditions or a fault that was already developing.
Temperature alone cannot identify the cause. Record the trend, load, speed and ambient condition, then compare vibration, noise, motor current and the observed outlet condition.
Next, verify the product, quantity, grease gun, feed point and outlet path.
Immediate checks
What to do before adding more grease.
Hold further lubrication while you establish the temperature trend and reconstruct the task.
- 01Follow procedure
Apply the asset operating and alarm procedure. Do not add more grease during the initial assessment.
- 02Record the trend
Note the pre-greasing value, current value, elapsed time and any change in load, speed or ambient conditions.
- 03Check related signals
Review vibration, ultrasound or noise, motor current, leakage and the specified outlet.
- 04Verify the task
Confirm product, compatibility, measured mass, grease-gun output, feed point and outlet path.
Why fresh grease can raise temperature
In many grease-lubricated arrangements, room is left in the housing for displaced grease. After replenishment, fresh grease redistributes through and away from the rolling path, temporarily increasing resistance and sometimes temperature.
If too much grease is present, or displaced grease cannot leave the working area, the elements continue to churn it. Churning consumes energy and generates heat. A short rise that settles is different from a climb that continues. Compare the curve with the asset's established baseline and operating limits.
Diagnostic map
Possible causes of a temperature rise after greasing.
Match the observed condition to the next check. Confirm the cause before changing the machine again.
| Possible explanation | Evidence to look for | Next controlled check |
|---|---|---|
| Excess grease or insufficient room for displacement | Rise begins after replenishment; the measured dose exceeds the instruction or cannot be reconstructed | Compare the controlled quantity with the OEM instruction; inspect the specified outlet condition |
| Blocked or incorrect outlet path | High gun resistance, hardened grease, a painted-over plug or the specified purge does not occur | Stop pumping; verify the feed and outlet route against the drawing or manual |
| Wrong or incompatible grease | Product changed, label is uncertain, leakage or stiffness appears after changeover | Stop the lubrication task; verify product approval, mix history and compatibility |
| Grease did not reach the bearing | Remote line, blocked fitting or misrouted passage; no expected change in companion signals after the task | Confirm the delivery route rather than assuming grease reached the rolling elements |
| Operating condition changed | Load, speed, ambient temperature, cooling or motor current changed with the trend | Compare readings at the same load, speed, ambient and cooling condition |
| Mechanical or bearing fault | Vibration, noise or motor current changes, or temperature continues to worsen after lubrication variables are verified | Escalate for mechanical condition assessment; do not add grease to suppress the symptom |
Excess grease or insufficient room for displacement
Blocked or incorrect outlet path
Wrong or incompatible grease
Grease did not reach the bearing
Operating condition changed
Mechanical or bearing fault
Temperature trend
Use the trend, not a single reading.
These curves are illustrative. They are not alarm limits and do not use a universal time scale.
Trace the lubrication event in order
Reconstruct the event before changing the machine again. Start with the grease cartridge or container: was it the approved product, clearly identified and within its storage controls? If the product changed, do not rely on a generic compatibility chart alone. Incompatible mixtures can soften and leak or stiffen and increase resistance.
Convert the delivered amount into a controlled unit. Stroke count is unreliable unless output from that gun, with that grease and a full stroke, has been verified by mass. Confirm that the fitting serves the intended bearing, the passage is open and the manufacturer-specified outlet was prepared correctly. Rising handle resistance can signal a restricted path. Do not use it to estimate quantity.
- Product name, grade and approval match the asset record
- Grease changeover and seal compatibility have been checked
- Delivered mass is based on the identified gun's current grams-per-stroke output
- The feed point and outlet path match the actual bearing arrangement
- Operating state and procedure match the equipment manual and site risk controls
Replenishment estimator
Estimate replenishment quantity from bearing dimensions.
This SKF-based estimate applies only to routine replenishment of applicable bearing arrangements. Confirm the feed route from the bearing drawing or machine manual before selecting a coefficient.
- Gp
- estimated replenishment quantity, grams
- D
- bearing outside diameter, mm
- B
- bearing width, mm, for the applicable radial bearing arrangement
No estimate is calculated until the required fields are complete.
Use the machine manufacturer's quantity when available. This SKF-based estimate covers routine replenishment only. Do not use it for sealed-for-life bearings, initial fill, relubrication intervals, automatic-system settings, flushing or product changeover. This version does not cover the T and H dimension conventions used for tapered roller and thrust bearings.
Give excess grease a safe exit path
A metered quantity still needs a viable path through the arrangement. A blocked, painted-over, hardened or incorrectly configured outlet can trap grease and pressure. Preparation, operating state, outlet handling and the time before reclosing vary by machine. There is no universal purge procedure or drain-open time.
Follow the instruction for the specific machine. Rotate or run only when that procedure authorizes it and the site controls permit the task. Open, clean and reclose the outlet as specified. Do not improvise with a wire or pump until fresh grease appears unless the manufacturer calls for a flushing procedure.
Escalation signals
When to stop monitoring and escalate.
Apply the site's operating, alarm or condition-monitoring response when any of these conditions appears.
- Temperature continues to rise or settles outside the asset's documented normal operating range
- A site or manufacturer alarm, trip or operating limit is reached
- Vibration, ultrasound, audible noise or motor current changes with the temperature
- The grease identity, amount or compatibility cannot be verified
- Grease leakage, smoke, an abnormal odor or visible seal distress appears
- The fitting or outlet path appears blocked, damaged or incorrectly configured
Update the work order after the event
If the team cannot reconstruct the product, amount, gun, time, load and outlet condition, the lubrication record is incomplete.
After the immediate event is addressed, update the task instructions with the approved grease, the quantity in the OEM-specified unit or verified grams where appropriate, the identified tool, feed point, outlet method, operating state, required observations and escalation rule.
Plant-floor record
Details to record on the work order.
- 01
Asset and bearing location
- 02
Approved grease product and batch/container identity
- 03
Measured grams delivered
- 04
Grease-gun ID and verified grams per full stroke
- 05
Time, load, speed and ambient condition
- 06
Temperature values with timestamps, including the peak
- 07
Vibration, ultrasound or audible noise, motor current, and outlet or purge observations
- 08
Action, owner and evidence required for closure
Record the deviation, action owner and closure evidence. If the point was inaccessible or the outlet unclear, correct the task design before the next route.
Common questions
Common questions about post-greasing temperature rise.
Is a temperature rise after greasing always overgreasing?
No. Excess grease and a restricted outlet are possible explanations, but a brief rise can occur while grease redistributes. Wrong or incompatible grease, a blocked feed route, seal drag, changed load or cooling, misalignment and bearing damage can produce similar symptoms. Use the trend and companion condition signals before deciding.
How hot is too hot for a greased bearing?
There is no single safe number for every bearing, grease, motor and operating condition. Use the equipment manufacturer's limits, the site's alarm response and the asset's established baseline. A continuing rise or a stable temperature above the asset's normal range should be investigated.
Should the outlet be left open for 30 or 60 minutes?
Do not apply a universal time. Motor and bearing procedures differ. Follow the machine-specific instruction for opening, cleaning, operating and reclosing that outlet.
Can we grease the bearing while the machine is running?
Only when the equipment procedure explicitly authorizes live relubrication and the guarding and site risk controls permit it. Some arrangements benefit from rotation during replenishment, while some motor manuals require a stationary, warm motor or prohibit live greasing.
Is the SKF Gp formula the exact grease dose?
No. It is a guideline replenishment quantity for defined delivery arrangements. The equipment nameplate, bearing arrangement and manufacturer instructions take priority. Use the formula as an engineering starting estimate only when the required dimensions and feed route are confirmed.
Primary references
These sources support the numerical guidance and procedure cautions used in this article.
- SKF: Grease relubrication procedures and replenishment quantities
- SKF: Rolling bearings, selecting grease or oil
- ABB: Installation and maintenance instructions for motors
- Timken: Bearing maintenance guidance
- NLGI: Grease compatibility and seal-compatibility FAQs
- NSK: Bearing operation inspection and abnormal-temperature checks
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