Do you have oil on the deck plate beneath your wind turbine generator and wonder where it is coming from? Or why does it keep coming back? That oil is often the first visible sign of a grease lubrication problem in your generator bearings, and it usually points to one root cause: grease oil and thickener separation.
What Grease Bleed Means
Grease is a blend of base oil, a thickener system, and performance additives. Oil separation, also known as “grease bleed”, occurs when the oil bleeds out of the thickener. Most greases exhibit some level of oil separation, which is required to lubricate moving components, especially under high loads where the grease is exposed to pressure between two connecting surfaces and the oil is effectively pushed out of the grease This oil‑bleeding property is also an essential performance characteristic for grease used in high‑speed applications. While some oil separation is normal and beneficial, excessive grease bleed can skew the ratio between oil, thickener, and additives, leaving behind a heavier, drier residue that can no longer maintain a reliable lubricating film in the bearing. This could also lead to line blockages within auto-lubrication systems and subsequent bearing starvation, as the fresh relubricating grease is prevented from reaching all critical contact surfaces. Once grease separates, the bearing is effectively running with insufficient lubrication even though “grease” is present.
A grease may exhibit more severe oil separation for a variety of reasons including
- Poor mechanical stability of the grease. High loads, vibrations, and additional application demands can break down its structure.
- High temperature exposure can cause excessive oil bleeding and accelerate the oxidation of the grease, especially when it is subjected to temperature peaks.
- Unbalanced formulations with limited thickener efficiency, low‑quality base oils, or insufficient additive content.
In wind turbine generators, high speeds and elevated temperatures accelerate this process. That is why it is critical to use grease specifically designed and engineered for wind turbine generators.
Why Oil on the Deck Plate is a Warning
Oil in the grease catch tray or on the deck plate, combined with the presence of grease lumps and the darkening of the running grease, generally indicates that the installed grease is breaking down and that the lubricating barrier in the generator bearing is compromised.
As more oil separates, the remaining grease dries out and the bearing must work harder to turn, driving up friction, heat, and further oil bleed. Simply adding more of the same grease does not fix the root cause; it only adds more grease that will separate in the same way.
The Risk of Ignoring Separation
If grease separation is not addressed, rising temperatures and vibration accelerate wear and can lead to premature generator bearing failure. Beyond repair costs, unplanned outages reduce production and require additional service climbs to rectify the issue.
A Grease Engineered for Generator Bearings
To break this cycle, generator bearings need a high-quality lubricant designed specifically for high-speed, high-temperature conditions. FUCHS developed GLEITMO XHD 2for wind turbine generator bearings and tested it extensively in generator applications and approved by both generator OEMs and turbine OEMs alike.
GLEITMO XHD 2 combines a full synthetic base oil with a high-temperature polyurea thickener to deliver low oil bleed while maintaining a stable, grease-like consistency at elevated temperatures. Additional benefits of GLEITMO XHD 2 include:
- Broad operating temperature range: -40 / +180°C; -40°F / +356°F
- Withstands short-term temperature spikes up to +200 °C/ 392 °F, providing additional safety margin compared to many standard generator greases.
- Excellent stability against ageing
- Excellent lubricity under vibrations, oscillations, shock loads
- Very good water resistance
- Good corrosion prevention
How GLEITMO XHD 2 Helps Reduce Downtime
In service, GLEITMO XHD 2 is engineered to resist oil separation, keeping the oil within the grease structure and at the rolling contacts instead of bleeding into grease traps or onto deck plates.
Dried out lithium synthetic grease in a wind generator bearing.
Wind generator bearing after using GLEITMO XHD 2 for 5 months.
In one documented case study, a customer was experiencing frequent generator bearing replacements because their existing grease was caking and hardening as oil separated. After switching to GLEITMO XHD 2, the grease maintained a stable consistency, significantly extending bearing life, increasing uptime, and reducing unplanned downtime.
Practical benefits for operators include:
- Improved bearing protection at high speeds and temperatures through low oil separation and stable grease consistency
- Fewer unplanned climbs and outages due to reduced relubrication needs and a lower risk of temperature alarms and premature bearing failure
- Reduced slip hazards and downtime due to less oil on the deck plate.
Oil on the deck plate or in the grease catch tray is more than a housekeeping issue—it is an early warning that grease separation is already putting generator bearings at risk. With GLEITMO XHD 2, operators can address the root cause, protect critical components, and keep turbines producing reliably over the long term.
Experiencing Similar Issues?
Seeing oil on the floor under your generator or in your generator slip ring box/housing? Let’s fix the cause, not the symptom. Stop grease separation before it stops your turbine. Talk to our experts.