A customer once asked us: “The gearbox temperature keeps rising during operation, and even changing to new oil didn’t help. What’s going on?” Today, let’s talk about gearbox overheating.
First, what counts as “too hot”?
Under normal operating conditions, gearbox bearing temperatures typically range between 50–70°C. In summer, if bearing temperatures consistently exceed 85°C, or in winter, consistently exceed 75°C, it indicates abnormal overheating that requires investigation.
What usually causes high temperatures?
Based on the frequency we encounter in the field, here are the most common causes:
- Lubricant issues (most common, but not the only cause)
Too little oil, too much oil, or the wrong oil grade can all lead to temperature rise.
· Too little oil: Gears and bearings don’t get adequate lubrication, causing friction heat to spike.
· Too much oil: Increased churning resistance causes the oil itself to generate heat from repeated agitation.
· Wrong oil grade: High-load applications require EP gear oil, e.g., ISO VG 320. If the viscosity is too low, the oil film breaks down under high pressure, metal-to-metal contact occurs, and temperatures rise rapidly.
- Bearing problems
As bearings wear, internal clearance increases, and rolling elements no longer run smoothly. Abnormal friction generates heat. If a bearing housing feels significantly hotter than other areas, bearing damage is likely the culprit.
- Overload operation
When actual operating torque exceeds the gearbox’s rated torque, gears and bearings are forced to work beyond their design limits, generating excessive heat. This is commonly seen when customers change their material formulation (e.g., increasing filler content) without upgrading the gearbox accordingly.
- Poor cooling conditions
High ambient workshop temperatures, poor ventilation, or excessive dust accumulation on the gearbox housing can all impede heat dissipation and contribute to temperature rise.
How does Kunka test on the test stand?
We monitor temperature throughout the entire test run of every gearbox. After a cold start, the temperature curve should rise steadily and then stabilize. If the temperature at any point keeps climbing without leveling off, we stop immediately to inspect bearing preload, gear mesh clearance, and lubrication condition — ensuring every gearbox leaves the factory with all parameters within specification.
Recommendations for customers
If you encounter temperature rise issues:
· Check oil level and oil grade – confirm they meet specifications.
· Feel the bearing housings – check whether temperatures are evenly distributed. A localized hot spot often points to bearing or gear damage.
· Check operating parameters – compare actual torque and speed against the gearbox rating.
· Inspect cooling conditions – improve ventilation and clean the housing if needed.
Still not sure what’s causing your gearbox to overheat? Send your model and operating data to Kunka Tech — we’ll help pinpoint the issue.