Staburags NBU 8 EP vs Mobilux EP 2: Heavy-Duty EP Grease Comparison

Staburags NBU 8 EP vs Mobilux EP 2: Heavy-Duty EP Grease Comparison

When selecting a heavy-duty extreme pressure (EP) grease for industrial rolling bearings, the choice of thickener chemistry and additive package directly influences bearing service life, relubrication intervals, and operational reliability. Two widely specified NLGI Grade 2 greases in this category are Staburags NBU 8 EP from Kluber Lubrication and Mobilux EP 2 from ExxonMobil. Although both are mineral-oil-based greases designed for high-load applications, they diverge significantly in thickener type, solid lubricant content, temperature capability, and water resistance characteristics. This article provides an educational, specification-driven comparison to help maintenance engineers and procurement professionals understand the technical trade-offs between these two products. We examine published datasheet values, relevant industry test standards, and the practical implications of each formulation for real-world bearing applications.

Technical Specification Comparison

Comparative Analysis: Load Capacity, Water Resistance, and Thermal Performance

Load-Carrying Capacity and EP Mechanisms

The two greases achieve extreme-pressure protection through fundamentally different mechanisms. Staburags NBU 8 EP relies on a combination of a barium complex soap thickener which itself contributes to load-carrying performance through the formation of a polar lubricating film on metal surfaces and molybdenum disulfide (MoS2) as a solid lubricant additive. MoS2 has a lamellar crystal structure that shears easily under load, providing emergency lubrication under boundary and mixed-film conditions where the fluid oil film collapses. This dual mechanism is particularly valuable in applications experiencing start-stop cycles, oscillating motion, or shock loading where full hydrodynamic film formation is not reliably maintained.

Mobilux EP 2, in contrast, employs a lithium hydroxystearate thickener combined with chemically active EP additives (typically sulfur-phosphorus compounds). These additives react with metal surfaces at elevated contact temperatures to form a sacrificial tribofilm that prevents welding and adhesive wear. The published quantitative EP values a Four-Ball Weld Point of 250 kgf (ASTM D2596) and a Timken OK Load of 40 lb (ASTM D2509) provide a standardized, repeatable benchmark for its EP capability. While the two greases cannot be directly compared via four-ball wear scar values (they are tested under different standards: NBU 8 EP at 1000 N for 1 minute per DIN 51350-5 versus Mobilux EP 2 at 392 N for 60 minutes per ASTM D2266), both demonstrate adequate load protection for heavy-duty industrial bearing applications within their respective design envelopes.

Water Resistance and Corrosion Protection

Water resistance is a critical property for bearings operating in wet, humid, or washdown environments, and here the thickener chemistry is decisive. Barium complex soaps are inherently hydrophobic and form a tenacious, adhesive structure that resists displacement by water. This gives NBU 8 EP robust water resistance without requiring supplementary additives, and the barium complex framework contributes simultaneously to corrosion inhibition. The product is described in Kluber documentation as water-resistant with reliable corrosion protection, though no quantitative washout or Emcor values are published in the standard datasheet.

Mobilux EP 2 uses a lithium thickener, which in its basic form has only moderate inherent water resistance. However, ExxonMobil formulates this grease with dedicated water-resistant additives that substantially improve its performance. The published SKF Emcor rust test result of 0-0 with distilled water (ASTM D6138) is a strong quantitative indicator of corrosion protection capability.

The product is described qualitatively as having excellent resistance to water wash-out. For applications where water resistance is paramount, Mobil also offers a specialized variant Mobilux EP 2-WR which achieves a water washout loss of approximately 4% at 79 C (SH/T 0109, equivalent to ASTM D1264). The standard EP 2 grade, while lacking a published washout figure, is widely accepted for use in wet industrial environments such as marine, mining, and pulp-and-paper operations.

Temperature Range and Thermal Stability

Thermal capability is one of the clearer differentiators between these two products. NBU 8 EP barium complex thickener provides a higher dropping point (>= 220 C) and a higher continuous upper service temperature (140 C) compared to Mobilux EP 2 190 C dropping point and 130 C upper limit. This temperature advantage is confirmed by the SKF-R2F Run B test at 140 C, which NBU 8 EP passes a demanding bearing test that evaluates grease performance at elevated temperature under load. NBU 8 EP also demonstrates approximately 4,000 operating hours in the SKF-ROF test at 120 C, providing a useful benchmark for estimating relubrication intervals in high-temperature rolling bearing applications. Mobilux EP 2 can be used above its 130 C recommended ceiling, but ExxonMobil advises that relubrication frequency must be increased accordingly a practical consideration for maintenance planning.

A notable difference in base oil viscosity also affects low-speed, high-load behavior. Mobilux EP 2 higher base oil viscosity (160 cSt at 40 C versus NBU 8 EP ~97 cSt) provides a thicker fluid film at low rotational speeds, which can be advantageous in slow-turning or heavily loaded plain bearings. NBU 8 EP lower viscosity, combined with a published speed factor of approximately 500,000 mm/min, makes it well-suited for higher-speed rolling bearing applications within its temperature range.

Application Guidance

Selecting between these two greases should be driven by the specific operating conditions of the application rather than a generalized preference for one product over the other.

Consider Staburags NBU 8 EP when the application involves continuously elevated temperatures above 130 C, when oscillating or start-stop motion demands the insurance of a solid lubricant (MoS2), or when mechanical stability at high temperature is a primary concern. The barium complex thickener inherent structural stability, combined with the MoS2 solid lubricant reserve, makes this grease a strong candidate for traction motors, hot-running electric motor bearings, kiln car bearings, and other applications where temperature and load combine to challenge conventional lithium greases. Applications involving journal bearings in rail vehicles, where the FAG FE9 and SKF-ROF data provide relevant validation, are also well-served by this formulation.

Consider Mobilux EP 2 when operating temperatures remain within the -20 C to 130 C window, when the published EP metrics (250 kgf weld, 40 lb Timken) align with the application load requirements, and when the extensive industry approvals (DIN 51825 KP 2 K-20, Volvo 97718, SEW-Eurodrive) simplify specification compliance. Its higher base oil viscosity offers advantages in slower-speed plain bearings, bushings, and pins where a thicker fluid film is desirable. The broad availability and competitive pricing of lithium-complex greases also make Mobilux EP 2 a practical choice for general heavy-duty industrial applications including construction equipment, mining machinery, and marine deck equipment where water exposure is intermittent rather than continuous.

Both greases require standard compatibility precautions. Barium complex and lithium thickener greases should not be mixed without verifying compatibility, as incompatibility can lead to softening, oil separation, and loss of lubricating performance. A thorough purging and cleaning procedure is recommended when switching between thickener types.

Key Takeaways

Staburags NBU 8 EP differentiates itself through its barium complex/MoS2 chemistry, delivering a higher continuous temperature ceiling (140 C versus 130 C), solid-film emergency lubrication, and a published bearing-life dataset (FAG FE9, SKF-ROF) that supports extended relubrication interval planning. Mobilux EP 2 counters with standardized, published EP metrics (250 kgf Four-Ball Weld, 40 lb Timken OK Load), a higher base oil viscosity favorable for low-speed applications, an Emcor 0-0 rust rating, and broad industry-approval coverage that simplifies procurement specification. Neither product carries H1 food-grade registration; NBU 8 EP is NSF-H2 registered for incidental non-food contact. The final selection should turn on the application specific temperature profile, speed range, water exposure, and whether solid lubricant content provides a meaningful operational safety margin.

KOEED Support

For technical inquiries, product availability, and pricing on Staburags NBU 8 EP, Mobilux EP 2, or alternative industrial greases, contact our team at Moritta@KOEED.COM. KOEED supplies industrial lubricants worldwide with global shipping options. Our technical team can assist with thickener compatibility assessments, application-specific grease selection, and cross-reference recommendations for legacy and obsolete specifications.