How to Read a Grease Datasheet
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How to Read a Grease Datasheet
Every industrial maintenance technician eventually faces the same moment: a grease datasheet lands on the desk, packed with numbers, abbreviations, and test method references that seem designed to confuse rather than inform. Worked penetration, dropping point, four-ball weld load, Timken OK load, water washout, oil separation -- these terms represent specific engineering tests that, when understood, paint a clear picture of how a grease will perform in service. Misreading them, on the other hand, leads to bearing failures that cascade into unplanned downtime. A pump bearing seizes because someone selected a grease with a dropping point far above the process temperature but base oil viscosity far too thin for the load. A conveyor bearing washes out in a food plant because the datasheet water washout number was never checked. This article walks through each major section of a typical grease datasheet, explains what the numbers mean in practical terms, and provides the framework needed to match grease specifications to real operating conditions. Every test method referenced here corresponds to published ASTM, ISO, or DIN standards that are maintained and updated by industry bodies; the interpretation guidance draws on bearing manufacturer engineering manuals, lubricant supplier technical publications, and established tribology literature.
Frequently Asked Questions
Q1: What are the main sections of a grease datasheet, and what does each one tell me?
A well-structured grease datasheet is organized into distinct functional blocks, each answering a different engineering question. The thickener and base oil section identifies the grease's chemical family -- lithium, lithium complex, calcium sulfonate, polyurea, aluminium complex, bentonite clay, or PTFE for the thickener, and mineral, PAO, ester, silicone, or PFPE for the base oil. This section tells you about compatibility with other greases, inherent temperature capability, and water resistance even before you see the numbers. The physical properties block covers worked penetration (NLGI grade), dropping point, and base oil viscosity at 40°C and 100°C. These are the foundational specification parameters that determine whether the grease can physically stay in place and lubricate at the bearing's operating conditions. The performance test data block reports extreme-pressure (EP) and anti-wear results: four-ball weld load, four-ball wear scar diameter, Timken OK load, and sometimes FZG gear test results. These numbers correspond directly to the grease's ability to prevent metal-to-metal contact under shock loads and sustained pressure. Environmental resistance tests -- water washout, oil separation, corrosion protection (Emcor or ASTM D1743), and oxidation stability -- predict how the grease behaves when exposed to contaminants, moisture, and sustained heat. The temperature range line gives the minimum and maximum service temperatures, which are engineering recommendations derived from test data rather than single-measurement results. Finally, the applications and approvals section lists industry specifications met (such as DIN 51825 K2K-30 or NLGI GC-LB) and manufacturer-specific approvals (such as SKF ROF or Siemens SN 29500 compliance). Each block answers a different question; evaluating a grease properly requires reading across all blocks, never fixating on a single number.
Q2: What is worked penetration, and how does the NLGI grade system work?
Worked penetration measures the consistency or stiffness of a grease -- essentially how hard or soft it is after being mechanically worked. The test, standardized as ASTM D217 and ISO 2137, involves filling a standardized cup with grease, then dropping a cone of specified weight and dimensions into the sample for five seconds. The depth the cone penetrates, measured in tenths of a millimetre, is the penetration value. The "worked" part means the grease has been subjected to 60 double strokes in a standardized worker block before measurement, simulating the initial mechanical shear the grease experiences when first distributed in a bearing. The NLGI (National Lubricating Grease Institute) grade system maps penetration ranges to numbers from 000 (fluid) to 6 (block-hard), with NLGI 2 being the most commonly specified grade for general industrial bearings. The full NLGI scale: NLGI 000 (445-475, nearly fluid like heavy oil), NLGI 00 (400-430, semi-fluid, used in centralized lubrication systems), NLGI 0 (355-385, very soft, for gearboxes and some centralized systems), NLGI 1 (310-340, soft, suitable for low-temperature or high-speed bearings), NLGI 2 (265-295, the standard for most rolling-element bearings in electric motors, pumps, and conveyor applications), NLGI 3 (220-250, firmer, used in vertical mounting positions and larger bearings where stiffer grease resists slumping), NLGI 4 (175-205), NLGI 5 (130-160), and NLGI 6 (85-115). Grades 4 through 6 are effectively hard greases used in special applications like open gears and certain types of couplings. The NLGI grade affects pumpability, channeling characteristics, and whether the grease stays in place. A common mistake is assuming firmer grease is always better -- an NLGI 3 grease in a high-speed spindle bearing can cause churning overheating, while an NLGI 1 grease in a large slow-speed thrust bearing may slump out of the housing. The NLGI grade must match the bearing type, speed, mounting orientation, and relubrication method.
Q3: What does dropping point tell me, and what does it NOT tell me?
Dropping point, determined by ASTM D2265 or the older D566 method, is the temperature at which a grease transitions from a semi-solid to a liquid state. In the test, a small grease sample is heated in a cup with a small orifice at the bottom; the dropping point is recorded when the first drop of oil or softened grease falls from the orifice. The dropping point is primarily a measure of the thickener's thermal stability -- the temperature at which the thickener structure collapses. Typical values are: simple lithium soap greases, approximately 175-195°C; lithium complex greases, approximately 260-280°C; calcium sulfonate complex greases, approximately 290°C and above; polyurea greases, approximately 240-270°C; organoclay greases, no measurable dropping point (clay does not melt). The critical engineering point is that dropping point is not a useable operating temperature. A widely accepted rule in lubrication engineering is to subtract 55-85°C from the dropping point to estimate the maximum continuous service temperature. This means a lithium complex grease with a 260°C dropping point has a practical continuous service ceiling of approximately 175°C. The gap exists because oxidation of the base oil, not thickener melting, is usually the failure mode. At temperatures well below the dropping point, the base oil oxidizes, thickens, and eventually forms hard carbonaceous deposits that destroy bearing surfaces. A study by ExxonMobil found no reliable correlation between dropping point values and actual grease life in dynamic bearing testing -- one grease with a lower dropping point outperformed a higher-dropping-point competitor in wheel-bearing life tests. For this reason, experienced engineers look for the manufacturer's published continuous service temperature rating, FE9 (DIN 51821) grease life data, and oxidation stability test results (ASTM D942 bomb oxidation test), not the dropping point in isolation. The dropping point is useful for one thing: confirming that the thickener system is stable enough for the application. If your bearing operates at 150°C and the grease has a dropping point of 160°C, you have a serious problem. If the dropping point is 280°C, you have an adequate thickener, but you must still verify that the base oil and additive package can survive 150°C.
Q4: What are the four-ball weld load and wear scar tests, and how do I interpret the results?
The four-ball test uses a pyramid of four steel balls -- one rotating ball on top pressing against three stationary balls below, immersed in the grease sample -- to evaluate extreme-pressure (EP) and anti-wear performance. Two distinct variants are reported on datasheets. The four-ball weld load (ASTM D2596) measures EP performance: the load is increased incrementally in a series of ten-second runs until the rotating ball welds to the three stationary balls. The weld point, reported in kilograms-force, represents the maximum load the lubricant can withstand before complete film failure and catastrophic metal-to-metal contact. Values above 250 kg are typical for EP-greased applications; values above 400 kg indicate strong EP additive chemistry; values above 620 kg (the machine's physical limit) are reported as "620+ kg." The four-ball wear scar (ASTM D2266) measures anti-wear performance under steady conditions: a single 40 kg load is applied for one hour at 1200 rpm and 75°C (or a specified temperature), after which the wear scars on the three stationary balls are measured under a microscope. The average diameter in millimetres is reported. Smaller wear scars indicate better anti-wear performance. An NLGI 2 general-purpose lithium grease without EP additives might produce a wear scar of 0.50-0.70 mm. A premium EP grease with anti-wear additives might produce 0.35-0.45 mm. Numbers below 0.40 mm are considered very good. Interpreting these two numbers together is important: a grease that welds at 500 kg (excellent EP) but produces a 0.70 mm wear scar (poor anti-wear) may protect against shock loads but cause gradual wear under normal running conditions. A grease with a 250 kg weld load (moderate EP) and a 0.35 mm wear scar (excellent anti-wear) may be better for steady-state precision bearing applications. The four-ball test is a screening tool, not a direct predictor of bearing life, but it is the most widely available EP and anti-wear comparison metric across different greases.
Q5: What is the water washout test, and how does it predict field performance in wet environments?
The water washout test (ASTM D1264) measures a grease's resistance to being physically displaced by water spray. In this test, a standardized ball bearing is packed with a specified amount of grease (typically 4.0 ± 0.1 grams), rotated at 600 rpm, and sprayed with water at a controlled rate (5 ± 0.5 ml per second) and temperature (typically 38°C or 79°C, depending on the specification) for one hour. The bearing is then dried and weighed; the percentage of grease washed out is calculated from the weight loss. A result of 5% or less indicates excellent water resistance, suitable for high-pressure washdown environments and submerged service. Results between 5% and 15% indicate good to moderate water resistance, suitable for outdoor equipment exposed to rain or process water splash. Results above 15% indicate the grease may wash out prematurely in wet environments and should be relubricated more frequently or reserved for dry applications. For food and beverage plants, dairies, wastewater treatment facilities, paper mills, and any outdoor equipment exposed to weather, the water washout number is one of the most important specifications on the datasheet. Calcium sulfonate complex greases consistently produce the lowest water washout values, often below 2%, because the thickener itself is water-resistant and adhesive. Lithium complex greases vary widely: premium formulations may deliver 3-7% washout, while basic formulations may exceed 15%. Polyurea greases generally perform well, with washout values in the 4-10% range. It is worth noting that water washout testing at the standard 38°C may not predict performance at higher water temperatures; if the application involves hot water or steam washdown, requesting water washout data at 79°C (ASTM D1264 provides for this variant) is recommended. The water spray-off test (ASTM D4049) provides a complementary measurement using a direct water spray at higher pressure, which can be more representative of high-pressure cleaning systems.
Q6: What is the oil separation test, and why does it matter for storage and bearing life?
The oil separation test measures how readily the base oil bleeds from the thickener matrix, which affects both storage stability and in-service lubrication performance. The most common method is ASTM D1742, in which a grease sample is placed in a standardized cone-shaped wire-mesh basket suspended over a collection dish. The assembly is heated to 100°C for 30 hours (older standard) or 25°C for 168 hours (ASTM D6184 long-term storage test), and the oil that separates and collects is weighed. Results are reported as a percentage of the original sample weight. For most industrial greases, oil separation between 1% and 5% under ASTM D1742 conditions is considered normal and even desirable -- some oil bleeding is necessary for the grease to lubricate bearing contacts. The rolling elements literally need a small amount of oil to separate from the thickener and form the lubricating film. Zero oil separation can indicate a grease that will starve the bearing of lubricant. Conversely, separation above 10-15% indicates instability: the grease may harden during extended storage, become unpumpable in centralized lubrication systems, or leave behind a dry soap plug that blocks relubrication pathways. In practice, the oil separation value influences several decisions. For centralized lubrication systems with long supply lines, greases with separation below 3-5% are specified to prevent oil-thickener separation during the extended residence time in the piping. For sealed-for-life bearings expected to operate for years without regreasing, low separation (1-3%) is specified together with high oxidation stability. For bearings that are relubricated frequently, slightly higher separation values (3-7%) are acceptable and may actually be beneficial. For bulk grease stored in drums for months or years, checking that the datasheet's stated oil separation is below the threshold at which the supplier recommends remixing is important. If a drum has been sitting for a year and the datasheet reports 12% oil separation at 100°C, there is a good chance a layer of separated oil has formed on top, and the grease may need reworking before use.
Q7: What is the Timken OK load, and when should I use it instead of the four-ball weld load?
The Timken OK load test (ASTM D2509) is an extreme-pressure test that uses a different geometry and contact configuration than the four-ball test, making it more representative of the line-contact conditions found in tapered roller bearings, thrust bearings, and gear teeth. In the Timken test, a hardened steel test cup (a ring) rotates against a stationary hardened steel test block, both immersed in the grease sample. The load is applied through a lever arm, and after each ten-minute run, the block is examined under a microscope for scoring -- visible damage to the surface. The OK load is the highest load in pounds-force (or converted to Newtons) at which the block passes without scoring. The next load increment, at which scoring occurs, is reported as the score load. Typical Timken OK load values: a basic lithium grease without EP additives may carry 20-30 pounds (9-14 kg). An EP lithium complex grease may carry 40-60 pounds (18-27 kg). Premium EP greases for heavy industrial applications (steel mills, mining, construction equipment) may carry 60 pounds and above. Some calcium sulfonate greases exhibit inherently high Timken loads of 60-80 pounds without added EP chemistry because the calcium carbonate crystal structure of the thickener provides a natural EP mechanism. The Timken OK load is particularly relevant for applications where the contact geometry is closer to line contact than point contact, which includes most tapered roller bearings, cylindrical roller bearings, and many gear tooth contacts. The four-ball test, by contrast, models point-contact geometry more typical of ball bearings. In practice, both numbers are useful. A grease that performs well on both the four-ball weld load and the Timken OK load tests has demonstrated EP capability across different contact geometries and can be specified with more confidence for mixed-bearing applications. When comparing two greases where one has a higher four-ball weld load but a lower Timken OK load than the other, the Timken number should usually carry more weight for roller bearing and gear applications due to the geometry similarity.
Q8: How do I read the base oil viscosity section, and why is it arguably the most important number on the sheet?
The base oil is the component that actually lubricates -- the thickener is merely the carrier that holds the oil in place and releases it gradually. Base oil viscosity determines film thickness in the bearing contact zone, which directly controls whether the bearing operates in hydrodynamic (full film), elastohydrodynamic (thin film), or boundary (metal-to-metal) lubrication regimes. The datasheet typically reports kinematic viscosity in centistokes (cSt) at 40°C and sometimes at 100°C. The viscosity at 40°C is the standard reference temperature and is used for the ISO VG classification: ISO VG 32 (28.8-35.2 cSt), ISO VG 46 (41.4-50.6 cSt), ISO VG 68 (61.2-74.8 cSt), ISO VG 100 (90-110 cSt), ISO VG 150 (135-165 cSt), ISO VG 220 (198-242 cSt), ISO VG 320 (288-352 cSt), ISO VG 460 (414-506 cSt), and so on. The viscosity index (VI), when provided, indicates how much the viscosity changes with temperature. A higher VI means the oil maintains its viscosity better as temperature increases. Mineral oils typically have a VI of 90-105. PAO synthetics range from 120-160. Some specialized ester and silicone oils exceed 200. To apply base oil viscosity to bearing selection, the bearing speed factor (ndm = bearing pitch diameter in mm multiplied by speed in rpm) is used. Lower speed factors require higher viscosity to maintain film thickness. For speed factors below 100,000, ISO VG 220-460 is commonly specified. For 100,000-400,000, ISO VG 68-220 is typical. Above 400,000, ISO VG 22-100 is used. The most common mistake when reading a datasheet is failing to check base oil viscosity at all -- selecting a grease with the right thickener, the right dropping point, and excellent EP numbers, but base oil viscosity that is completely wrong for the bearing size and speed. No additive package can compensate for a base oil viscosity that cannot physically build a lubricating film.
Q9: What thickener types are common, and how can I identify them from the datasheet?
The thickener type is usually stated explicitly in the product description or the composition section of the datasheet, but when it is not, the dropping point and water resistance data often provide strong clues. Lithium soap (simple lithium) greases have dropping points of 175-195°C, moderate water resistance, and are typically the most economical industrial greases. They are suitable for general-purpose bearing lubrication up to approximately 100-120°C. Lithium complex greases have dropping points of 260°C and above, improved high-temperature capability (to approximately 150-175°C continuous), and better mechanical stability than simple lithium greases. They are the most widely used multi-purpose industrial greases. Calcium sulfonate complex greases have the highest dropping points among common thickeners at 290°C+, inherently low water washout numbers (often below 2%), built-in EP and anti-corrosion properties from the calcium carbonate crystal structure, and a characteristic smooth, buttery appearance. They are the recommended choice for wet, washdown, and corrosive environments. Polyurea thickeners are ashless, typically deliver three to five times longer service life than lithium complex in sealed bearings at elevated temperatures, and are the standard for factory-filled electric motor bearings and many automotive applications. They have dropping points of 240-270°C. Aluminium complex greases have dropping points of approximately 260°C, excellent water resistance, and a characteristic stringy or tacky consistency. They are commonly specified in food-grade applications. Organoclay (bentonite) thickeners have no defined dropping point since clay does not melt, giving them structural stability at extreme temperatures where the practical limit becomes the base oil, not the thickener. PTFE-thickened greases, used with PFPE base oils, serve the extreme high-temperature range above 230°C. When the datasheet does not explicitly name the thickener, the dropping point, water washout percentage, and the presence or absence of EP additives provide strong diagnostic clues for identification.
Q10: What does the operating temperature range on the datasheet actually represent?
The operating temperature range reported on a grease datasheet consists of a minimum and maximum value, and each endpoint has a distinct physical basis. The minimum service temperature is primarily determined by the base oil's pour point and, increasingly, by the low-temperature torque characteristics of the grease as a whole. The rule of thumb is that the minimum usable temperature is approximately 10-15°C above the base oil pour point. For a grease with a mineral base oil having a pour point of -15°C, the practical low-temperature limit is around 0°C. For a PAO synthetic base oil with a pour point of -50°C or below, the grease may function down to -40°C. ASTM D1478 low-temperature torque testing provides the definitive measurement: the starting torque and running torque after one hour at the specified low temperature must both be below specified limits for the grease to be rated for that temperature. The maximum service temperature on the datasheet is the manufacturer's engineering recommendation based on the thickener thermal stability (dropping point), base oil oxidation resistance, and additive package thermal durability. It is always substantially below the dropping point. A well-formulated lithium complex grease may carry a maximum continuous service rating of 150-175°C despite a 260°C+ dropping point. The temperature range on a datasheet is not a guarantee of adequate bearing life at the extremes -- it defines the envelope within which the grease can function without immediate degradation. Operating continuously at the upper end of the stated range will shorten relubrication intervals dramatically. The oxidation rate approximately doubles for every 10°C increase in temperature above approximately 70°C, so a grease that lasts 3,000 hours at 80°C may need regreasing every 200-300 hours at 120°C. When comparing datasheets between manufacturers, it is important to note that there is no industry-standard method for determining the maximum service temperature rating; different manufacturers use different criteria (some based on oxidation stability testing, others based on field experience, others based on FE9 grease life data). Whenever possible, request the specific test data or field references supporting the temperature claim.
Q11: What additive information should I look for, and where is it typically reported?
Additive information is often the least transparent section of a grease datasheet because manufacturers treat additive chemistry as proprietary. However, several additive performance indicators are reported through standardized tests. EP (extreme-pressure) additives, typically sulfur-phosphorus compounds, zinc dialkyldithiophosphates (ZDDP), or solid lubricants such as molybdenum disulfide and graphite, are inferred from the four-ball weld load and Timken OK load results rather than listed by chemical name. If the weld load exceeds 250 kg or the Timken OK load exceeds 40 pounds, the grease almost certainly contains EP additives. Anti-wear additives (typically ZDDP or ashless organophosphates) are indicated by the four-ball wear scar diameter -- values below 0.45 mm suggest effective anti-wear chemistry. Anti-oxidant additives (typically amine or phenolic types) are evidenced by the ASTM D942 bomb oxidation test: a pressure drop of less than 35 kPa (5 psi) after 100 hours at 99°C indicates good oxidation stability. Rust and corrosion inhibitors are demonstrated by ASTM D1743 (bearing corrosion test) or the Emcor test (ISO 11007 / DIN 51802), where a rating of 0-0 or 1-1 indicates excellent corrosion protection. Tackiness additives, used to improve adhesion and reduce water washout, are indicated by water washout values below 5% and can sometimes be identified in the composition description as "polymer" or "tackifier." The absence of certain additives is also important: for electric motor bearings, the absence of metallic EP additives reduces the risk of bearing current discharge damage; polyurea greases without EP additives are commonly specified for this reason. For food-grade applications, the NSF H1 registration number confirms that all additives meet FDA 21 CFR 178.3570 requirements for incidental food contact. If a specific additive performance characteristic is critical to your application and the datasheet does not provide clear data, contacting the manufacturer's technical support is the recommended course of action rather than inferring additive content from generic product category assumptions.
Q12: How do I compare two grease datasheets systematically to choose the right product?
A systematic comparison follows a checklist that matches datasheet values to operating requirements in order of priority. Step one: verify thickener type and base oil. Are the thickener and base oil compatible with the existing grease in the bearing, and are they chemically suitable for the environment (water, chemicals, food contact)? Step two: check base oil viscosity at 40°C. Calculate the bearing speed factor (ndm) and confirm the viscosity is in the correct range for the bearing size and speed combination. This is the most frequently overlooked step and the most common cause of lubrication-related bearing failures at the selection stage. Step three: confirm the NLGI grade matches the application's mechanical requirements -- bearing type, speed, mounting orientation, and relubrication method. Step four: verify the temperature range. The continuous service temperature of the application should fall comfortably inside the manufacturer's stated range, not at its edge. Step five: check EP and anti-wear performance. Compare four-ball weld load, four-ball wear scar, and Timken OK load. For applications with shock loads, prioritize weld load and Timken OK load. For steady-state precision applications, prioritize wear scar. Step six: check environmental resistance. If water exposure is present, compare water washout percentages and Emcor corrosion ratings. If the grease will be stored for extended periods, compare oil separation percentages. Step seven: verify relevant industry approvals and OEM specifications. If the bearing manufacturer specifies a particular grease standard or the motor manufacturer requires a specific approval, the datasheet should state compliance explicitly. Step eight: calculate total cost of ownership. A grease that costs twice as much per kilogram but extends relubrication intervals from monthly to quarterly and eliminates one bearing replacement per year is almost always the lower-cost option when labour, downtime, and parts are accounted for. Going through this checklist systematically prevents the common error of fixating on one impressive number (such as a high dropping point) while missing a disqualifying characteristic (such as base oil viscosity that is completely wrong for the application).
Key Takeaways
Reading a grease datasheet is a skill that combines understanding standardized test methods with practical bearing engineering knowledge. The base oil viscosity is the single most important number for ensuring adequate lubricating film thickness. The NLGI grade determines pumpability and whether the grease stays in place. Dropping point confirms thickener thermal stability but does not predict bearing life -- use the manufacturer's continuous service temperature rating instead. Four-ball and Timken tests provide a comparative screening of EP and anti-wear performance, with Timken being more representative of line-contact bearing geometry. Water washout and oil separation predict environmental resistance and storage stability respectively. No single number on a datasheet tells the full story; evaluating a grease properly requires reading across all sections and matching the complete profile to your specific bearing type, speed, load, temperature, and environmental conditions. When in doubt, contact the lubricant manufacturer's application engineering team with your detailed operating parameters for a data-backed recommendation.
KOEED Technical Support
Selecting the right grease for your industrial application requires matching datasheet specifications to real operating conditions. KOEED's technical team can help you interpret grease datasheets, compare products across manufacturers, and identify the appropriate lubricant for your specific equipment. Contact Moritta@KOEED.COM with your bearing types, operating temperatures, speeds, loads, and environmental conditions for application-specific guidance. KLUBER ISOFLEX, Klüberplex, BARRIERTA, STABURAGS, and Klübersynth datasheets and technical documentation are available on request.