Category: Technical

NLGI grade is the first spec line every buyer reads, and the one most often misunderstood. The number tells you the consistency of the grease – how stiff it is at 25 °C – measured by cone penetration (ASTM D217). It does not tell you the thickener type, the base oil viscosity or the temperature ceiling. Two NLGI 2 greases can behave completely differently in the field.

What the numbers actually mean

The scale runs from 000 (semi-fluid, like thick oil) to 6 (block grease, nearly solid). Each step roughly halves the penetration depth:

• NLGI 000 – 00: Semi-fluid. Flows under gravity. Used in enclosed gearboxes and centralised systems where the grease must travel through long lines.
• NLGI 0 – 1: Very soft. Pumps easily at low temperature. Common in centralised lubrication for chassis points, and in high-speed bearings where churning losses matter.
• NLGI 2: The industry standard. Soft enough to pump, stiff enough to stay put. Fits roughly 80% of general industrial bearings.
• NLGI 3: Stiffer. Used where vibration or vertical shafts would wash a softer grease out of the raceway, and in pre-packed double-sealed bearings.

A practical selection map

Centralised systems (long pipe runs, multi-point): NLGI 00 – 1. The grease must flow through 10-30 m of line at ambient temperature. A stiff NLGI 2 will leave far-end points starved.

Electric motor bearings (1,800 – 3,600 rpm): NLGI 2 or 3 with a polyurea or lithium thickener. Softer grades churn, overheat and leak past shields.

Slow, heavily loaded plain bearings: NLGI 1 – 2 with high base-oil viscosity. Consistency matters less than film strength here.

Gearboxes (enclosed): NLGI 000 – 00 semi-fluid greases, or switch to gear oil entirely above certain speeds.

Vertical shafts and vibrating screens: NLGI 3. Gravity and vibration are working against you.

Low temperature changes everything

Consistency is measured at 25 °C. At -20 °C the same grease is far stiffer – and may not pump at all. If your equipment winters outdoors, check the low-temperature torque spec, not just the NLGI grade. Our lithium line, for example, stays pumpable to -30 °C in NLGI 1.

What we stock

LLF Grease manufactures the full range: NLGI 000 semi-fluid gearbox greases, NLGI 0/1 centralised-system grades, NLGI 2 workhorse lithium and polyurea, and NLGI 3 for high-vibration positions. Every batch ships with a COA listing the exact penetration value, so you know what arrived – not just what the brochure says.

Not sure which grade your application needs? Send us the bearing type, speed and ambient temperature range – our engineers will recommend a grade and provide free samples for testing.

Ask three suppliers which thickener is “best” and you will get three different answers – usually the one they sell. The honest answer is that each thickener family wins in a specific environment. Here is the comparison that actually matters, field-tested across our 28 years of production.

Lithium (the all-rounder)

Lithium 12-hydroxystearate thickeners cover the widest application window at the lowest cost. Dropping point around 190-200 °C, good water resistance (not great), excellent shear stability, and compatible with most other lithium and lithium-complex greases.

Choose lithium when: the application is general machinery, temperature stays under 120 °C continuous, and cost per kilogram matters. Our lithium line covers NLGI 000 to 3, including EP and semi-fluid versions.

Polyurea (the high-temperature specialist)

Polyurea thickeners are sheared from an in-situ reaction, giving a dropping point of 250 °C+ and outstanding oxidation resistance – the grease does not need antioxidant top-ups to survive long bearing life. Electric motor manufacturers standardised on polyurea decades ago for “sealed for life” bearings.

Choose polyurea when: relubrication is difficult or impossible (sealed bearings), temperatures run 150-200 °C continuous, or you need 20,000+ hour bearing life. The trade-offs: polyurea does not mix safely with lithium or calcium greases, and it is more expensive per kilogram.

Calcium (the water fighter)

Conventional calcium grease softens above 80-90 °C but is nearly waterproof. Anhydrous calcium – the type we produce – pushes the dropping point to 140-150 °C while keeping the exceptional water washout resistance: under 5% loss in the ASTM D1264 test.

Choose calcium when: water is everywhere – mining slurry, marine equipment, water pumps, food processing washdowns. Nothing else survives constant water contact as well at this price point.

Head-to-head summary

The mixing trap

One warning that outranks everything above: polyurea and lithium/calcium greases are generally incompatible. Topping a polyurea-filled motor bearing with lithium grease can liquefy the matrix and dump both into the windings. If you inherit equipment and do not know what is inside, flush or relubricate aggressively until the old grease is purged.

We manufacture all three families and will tell you honestly which one your application needs – sometimes that means recommending the cheaper one. Request samples of each for side-by-side bench testing.

It happens on every maintenance floor: the specified grease is out of stock, a similar-looking pail is on the shelf, and the bearing gets topped up with whatever is available. Three weeks later the bearing runs hot, grease leaks past the seals, and nobody connects it to that one-time substitution.

What actually happens when greases mix

A grease is roughly 80% oil held in a thickener scaffold. Two greases mix badly in one of two ways:

• Matrix collapse: The new grease’s thickener interacts with the old one’s, and the scaffold loses rigidity. The grease softens dramatically and flows out of the bearing – leaving it unlubricated. Lithium meeting polyurea is the classic case.
• Matrix hardening: The opposite failure – the blend stiffens, the bearing starves, and churning heat builds up.

Either way the failure is delayed and quiet, which is exactly why mixing damage rarely gets diagnosed as mixing damage.

The compatibility chart (simplified)

“Caution” = test before committing; failing pairs exist within these families. “Check” here means “check with the manufacturer” – do not assume.

Field rules that prevent 90% of failures

1. Same thickener + same base oil family = usually safe. Still verify EP additives don’t clash (e.g., some moly and some overbased sulfonates interact).
2. Unknown history = purge, don’t top up. Relubricate at short intervals 3-4 times to push the old charge out before resuming normal intervals.
3. Colour and texture mean nothing. Two red greases can be lithium and polyurea.
4. When in doubt, ask for the compatibility statement. We issue written compatibility guidance for our grades against all major competitors’ products.

What if the mix already happened?

Signs to watch: grease leaking from seals that never leaked before, bearing temperature up 10-15 °C with no load change, or discoloured soft grease at the relief port. Response: stop relubricating with the new product, purge with the original grease at 2-3x normal quantity over several sessions, and inspect the bearing at the next window.

Our technical team handles mixing incidents weekly. Send us photos of the grease in the bearing and the product labels involved, and we will tell you whether you have a problem and how to purge it.