Grease Selection Guide: Types, NLGI & EP

Grease Types & Selection Guide: Lithium, EP, NLGI Grades & Compatibility

Pick up two tubs of industrial grease from the same shelf and they may look identical — same colour, same consistency, same NLGI grade — and be completely incompatible. Mix them in a bearing housing and you can turn a reliable bearing into a failed one within a single shift. That's not an edge case; it's one of the most common causes of premature bearing failure in industrial maintenance.

Grease selection is not complicated, but it requires understanding three things: what grease is actually made of, how to read the specification, and why mixing greases is a decision that needs to be made deliberately rather than by default. Get those three things right and greasing becomes systematic rather than guesswork.

This guide covers every selection variable: thickener types, NLGI consistency grades, extreme pressure additives, temperature limits, food grade classifications, and the compatibility rules that determine what you can and cannot mix. There is also an application table to translate all of it into practical decisions for the most common industrial use cases.

What grease is made of

Grease is not oil with something added to make it thick. It is a structured product with three distinct components, and each plays a different role:

• Base oil — typically 75–95% of the total weight. The base oil is the actual lubricant — the film that separates surfaces and prevents metal-to-metal contact. Base oil viscosity is the primary determinant of load-carrying capacity and temperature performance. Most industrial greases use mineral base oil; high-performance greases may use PAO (polyalphaolefin) synthetic or ester synthetic base oils for extended temperature range and service life.
• Thickener — typically 3–30% of the total weight. The thickener is a solid or semi-solid matrix that holds the base oil in place and releases it gradually under shear at the lubrication point. The thickener is what makes grease a grease rather than an oil. Thickener type is the most critical selection variable — it determines temperature range, water resistance, and compatibility with other greases. Common thickeners include lithium soap, lithium complex, calcium soap, calcium sulphonate, polyurea, and bentone (clay).
• Additives — typically 1–10% of the total weight. Additives modify specific performance properties: extreme pressure (EP) additives improve load capacity under shock loading; anti-wear additives protect surfaces at low speed or boundary lubrication conditions; anti-oxidants extend service life; rust inhibitors protect ferrous surfaces from corrosion; tackifiers improve adhesion and resist fling-off; anti-foam agents prevent aeration in high-speed applications.

The practical takeaway: two greases with the same NLGI grade and the same base oil viscosity can be incompatible if their thickeners are different. Specification matching must include the thickener type, not just the grade number.

Thickener types

The thickener is what most people mean when they say "type of grease." Understanding the main thickener families — their strengths, limits, and compatibility relationships — is the foundation of grease selection.

Lithium grease — the default for good reason

Simple lithium soap grease is the most widely used thickener type in the world, and for most general industrial applications, it is the correct default. It offers a good balance of temperature range, water resistance, mechanical stability, and cost. The drop point (the temperature at which the thickener structure collapses and the grease liquefies) is typically 175–200°C, giving a working maximum of around 120–130°C with reasonable service life.

Lithium complex grease uses complexing agents during manufacture that raise the drop point above 260°C, extending the working temperature range to 150–180°C. Lithium complex is the appropriate upgrade when operating temperatures exceed the limits of simple lithium — not as a universal "better" choice, since it costs more and the compatibility matrix is slightly more complex.

Calcium sulphonate — the specialist for severe conditions

Calcium sulphonate complex grease has an unusual property: it provides inherent extreme pressure performance without sulphur-phosphorus EP additives. This makes it suitable for environments where conventional EP additives would degrade (very high temperatures, contact with water) or where sulphur-active metals must be protected. It also has outstanding water resistance, making it the preferred choice for steel mill work rolls, paper mill bearings, marine shafting, and mining equipment exposed to constant water contamination.

Polyurea — excellent but incompatible

Polyurea thickeners deliver excellent high-temperature performance, oxidation resistance, and compatibility with the seal materials common in electric motors and sealed bearings. For this reason, polyurea NLGI 2 grease is the factory fill in the majority of sealed electric motor bearings, and many bearing manufacturers specify it as the recommended re-grease product.

The critical caveat: polyurea grease is incompatible with virtually all soap-based greases (lithium, lithium complex, calcium, sodium, aluminium complex). Mixing polyurea with lithium grease in a bearing housing can cause catastrophic softening or hardening within hours of startup, leading to rapid bearing failure. If an electric motor bearing is originally filled with polyurea grease, re-greasing must use polyurea grease — or the bearing must be thoroughly cleaned and repacked. Assuming "any NLGI 2 grease will do" in a motor bearing is a common and expensive mistake.

NLGI consistency grades

The National Lubricating Grease Institute (NLGI) consistency grade describes how stiff the grease is at 25°C. It is measured by the ASTM D217 cone penetration test — a weighted cone is dropped into the grease and the depth of penetration determines the grade. Lower numbers are softer (more fluid); higher numbers are stiffer.

NLGI 2 — the default for most applications

NLGI 2 is the correct starting point for most rolling element bearings operating at moderate speed and load. If the equipment documentation specifies no grade, and the operating conditions are unremarkable, NLGI 2 lithium or lithium complex grease is the default. The only common reasons to deviate from NLGI 2 are:

• NLGI 1 or 0: Required for low-temperature operation (below about −15°C) where NLGI 2 may be too stiff to distribute properly, or for high-speed bearings where a softer grease generates less churning heat.
• NLGI 3: Appropriate for high-load, low-speed applications (slow conveyors, vertical shaft bearings, heavily loaded wheel bearings) where a stiffer grease provides better retention and resistance to purging under load.
• NLGI 0 or 000: Required for centralised automatic lubrication systems where the grease must pump reliably through pipes and distribution fittings, often over long distances.

EP additives and additive packages

Extreme Pressure (EP) additives are chemical compounds — typically sulphur, phosphorus, or chlorine-based — that activate under high contact stress and high surface temperature to form a sacrificial boundary film on metal surfaces. This film prevents welding and scuffing under shock loads or slow, heavily loaded sliding contact where the hydrodynamic oil film would otherwise collapse.

EP is an additive package, not a thickener type. This is the most common misconception in grease specification. "EP grease" means grease with extreme pressure additives; it does not say anything about whether the thickener is lithium, calcium, polyurea, or anything else. "Lithium EP 2" means: lithium thickener + EP additives + NLGI grade 2. Both axes must be specified.

When EP is required

• Heavily loaded sliding contact: open gears, rack and pinion, ball and socket joints, chassis pivots
• Slow, high-load rolling element bearings: large industrial bearings operating below their speed rating with high radial or axial loads
• Shock and impact loading: crushers, presses, hammers
• Spline and coupling lubrication

When EP is not required (and may be detrimental)

• High-speed, lightly loaded rolling element bearings — EP additives are not needed and some sulphur-based EP additives can attack yellow metals (copper, brass, bronze) in bearings or housings
• Applications with copper alloy components — confirm compatibility before using sulphur-active EP greases
• Food grade applications — most conventional EP additives are not approved for incidental food contact

Operating temperature

Temperature is one of the most important grease selection variables, and it is frequently underestimated. There are two temperatures that matter:

• Dropping point — the temperature at which the thickener structure irreversibly collapses and the grease becomes a liquid. This is a laboratory measurement. The dropping point is not the maximum use temperature; it is the failure point.
• Maximum continuous use temperature — typically 30–50°C below the dropping point, accounting for the fact that grease at the dropping point is already degraded before it liquefies. Sustained operation above the maximum continuous use temperature causes rapid oxidation of the base oil, hardening of the thickener, and loss of lubrication.

A useful rule of thumb from bearing technology: grease service life approximately halves for every 10°C increase in bearing operating temperature above 70°C. A bearing running at 90°C will need re-greasing twice as often as the same bearing running at 70°C — and a bearing running at 110°C will need re-greasing four times as often.

Note that bentone (clay) thickeners have no drop point — the thickener does not melt. This makes bentone greases technically useful at very high temperatures, but the base oil still oxidises at sustained elevated temperatures, so the practical maximum is still determined by base oil stability.

Application guide

The table below translates the selection variables into practical recommendations for the most common industrial applications. These are starting points — always verify against the equipment manufacturer's specification where it exists.

Grease compatibility — the mixing warning

When greases of different thickener types are mixed — either during a product changeover, when topping up without purging, or when an old and new grease meet in a bearing housing — the result can range from no effect to catastrophic failure depending on which two thickener types are involved.

The mechanism varies. In some combinations the thickener structures interact chemically, causing the grease to soften dramatically and lose its ability to stay in place. In others the mixture hardens, blocking re-lubrication channels. In either case the base oil can separate from the thickener, depriving the bearing of lubrication.

The compatibility matrix

✅ Generally compatible | ⚠️ Borderline — test before use | ❌ Incompatible — do not mix

Important caveat: Compatibility charts are a starting point, not a guarantee. A 2017 review of 17 published compatibility charts found significant contradictions between sources for several thickener combinations. The chart above reflects general consensus, but additive packages and base oil types within the same thickener family can change the outcome. When switching grease products on critical equipment, the safest approach is to clean and repack rather than top up.

What to do when changing grease types

If you need to switch from one thickener type to another — for example, moving from simple lithium to calcium sulphonate on a bearing exposed to water — the correct procedure is:

1. Remove the bearing from service if possible.
2. Clean out as much of the old grease as possible — disassemble and wipe, or flush with a compatible solvent.
3. Repack with the new grease.
4. If disassembly is not practical, purge by re-greasing repeatedly with the new product until the old grease is fully displaced and only the new grease exits the relief valve or purge point. Verify by colour or consistency if the two products are visibly different.

For the polyurea/soap combination: do not attempt a purge procedure — the risk of the mixed zone causing bearing failure during the transition is real. Disassemble and repack.

Food grade greases

Food grade greases are required in food processing, beverage, pharmaceutical, and packaging operations wherever lubricant could come into contact with food or food-contact surfaces. They are classified by NSF International (formerly the National Sanitation Foundation) under three categories:

• NSF H1 — lubricants that may have incidental, technically unavoidable contact with food. This is the most commonly required classification for bearings, gearboxes, and conveyor components in food processing environments. H1 lubricants use food-safe thickeners (commonly aluminium complex or calcium sulphonate) and white mineral or PAO synthetic base oils.
• NSF H2 — lubricants used in areas with no possibility of food contact (machine room, external surfaces). H2 products are food-safe by formulation but not approved for incidental food contact.
• NSF H3 — edible oils or soluble oils used to clean and prevent rust on hooks, trolleys, and equipment that contacts food. Not a lubricating grease category.

For all food processing bearing and machinery lubrication: specify NSF H1 rated products. H2 is not sufficient for in-plant equipment where product or packaging contact is possible. The NSF H1 rating must appear on the product label or technical data sheet — do not rely on a supplier's verbal assurance.

A quality NSF H1 grease performs comparably to a conventional industrial grease of the same grade and thickener type under normal conditions. The performance compromise in food grade products is real at extreme temperatures or loads, but for most food processing environments operating at moderate speeds and temperatures, H1 greases are fully capable.

Dielectric grease

Dielectric grease is frequently searched in the same context as bearing and industrial greases, so it is worth being clear about what it is and what it is not.

Dielectric grease is a silicone-based compound — typically silicone oil thickened with silica or a silicone wax — formulated to seal, insulate, and protect electrical connections. It is applied to spark plug boots, battery terminals, trailer connectors, switch contacts, and other electrical connection points to exclude moisture, prevent corrosion, and reduce the risk of arcing. It is not a lubricant in the bearing or machinery sense.

The name "dielectric" refers to its electrical insulating properties — it does not conduct electricity and is used specifically because it will not short-circuit the connections it protects.

Do not use dielectric grease as a bearing lubricant. Silicone grease has very poor mechanical stability under the shear and load conditions inside a bearing — the film it produces is inadequate for rolling contact loads, and its viscosity characteristics are not suited to either rolling or sliding lubrication under machinery conditions.

The correct use of dielectric grease is electrical connection protection only.

How to re-grease correctly

Both under-greasing and over-greasing damage bearings — over-greasing is actually the more common cause of failure in maintained equipment, because it is less obvious. Understanding what happens inside a bearing housing explains why quantity and method both matter.

What over-greasing does

Bearings do not run in a housing full of grease. They run in a partially filled housing where only enough grease contacts the rolling elements to maintain the oil film. When a housing is over-filled with grease, the rolling elements churn through excess grease rather than running freely. This generates heat — sometimes enough to accelerate bearing wear faster than running dry would — and the churning pressure can force grease past seals, creating contamination pathways and seal damage.

The rule of thumb for grease fill volume in a bearing housing is 30–50% of the free space at installation. The remaining space allows the grease to distribute, consolidate, and bleed oil without churning. For sealed-for-life bearings, this is handled by the manufacturer at assembly — do not attempt to add grease to a sealed bearing.

Re-greasing quantity

For re-greasing an open bearing in service, a rough starting formula for grease quantity is:

G (grams) = 0.005 × D × B

Where D = bearing outside diameter in mm, B = bearing width in mm. This is an approximation — use the equipment manufacturer's specification where available. Most bearing manufacturers publish re-greasing quantities and intervals in their catalogues for each bearing size and operating condition.

Re-greasing frequency

Re-greasing frequency is determined by bearing size, speed, temperature, contamination level, and grease type. As a general guide, the hotter and faster a bearing runs, the more frequently it needs re-greasing. Grease service life halves for every 10°C above 70°C — a bearing running at 90°C needs re-greasing twice as often as the same bearing at 70°C.

For sealed and shielded bearings: these are not designed to be re-greased. They contain a calculated fill quantity at manufacture. Re-greasing attempts typically over-fill the housing and damage the seals. When sealed bearing grease life is exhausted, replace the bearing.

Grease nipples and application

Apply grease slowly through the grease nipple with the bearing running where safe to do so — this distributes the new grease evenly and allows displaced old grease to exit the relief valve. Applying grease rapidly to a cold, stationary bearing can build pressure that forces seals outward. If a relief valve is present, leave it open during re-greasing and close after the new grease appears at the outlet. See our comprehensive Grease Gun Guide for selection across manual lever, pneumatic and battery models, or the deep-dive Macnaught K29 Flexigun article for K29-specific technique.

Choosing the right grease is the first step; applying and replenishing it correctly is the second. The bearing maintenance guide covers inspection intervals, relubrication procedures and storage best practices for all common industrial bearing types.

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