What Is Moly Grease?
Moly grease is a conventional grease — typically a lithium or lithium complex base — infused with molybdenum disulphide (MoS2) at concentrations of 1–5% by weight. MoS2 is a naturally occurring mineral, dark grey to black in colour, milled to a very fine particle size (typically 1–5 microns). The MoS2 doesn't replace the grease; it works alongside it as a solid lubricant additive, providing a second line of defence when the grease film thins under extreme pressure, slow speed, or shock loading.
You'll see it sold under names including moly grease, molybdenum grease, MoS2 grease, and — in older Australian trade contexts — moly EP grease. The product is visually unmistakable: the dark grey or near-black colour is permanent and unavoidable. If you're working with moly grease, wear gloves — it stains hands, clothing, and bench surfaces persistently.
Moly grease is a specialist tool, not a universal replacement for standard grease. Understanding exactly where it excels — and where it causes damage — is the entire point of this guide.
How MoS2 Works: The Lamellar Barrier Mechanism
To understand when to use moly grease, you need to understand why MoS2 works at all. The answer is in the crystal structure.
MoS2 has a hexagonal layered structure: sheets of molybdenum atoms sandwiched between layers of sulphur atoms, held together by weak van der Waals forces. Under pressure, these layers slide over each other with almost no resistance — like a deck of greased playing cards under a heavy weight. This is the lamellar barrier mechanism.
The coefficient of friction for MoS2 is approximately 0.025. To put that in context: steel on steel is roughly 0.6–0.8. PTFE (Teflon) sits around 0.04. MoS2 is one of the lowest-friction solid materials known.
When moly grease is applied to a metal surface under load, the MoS2 particles physically plate out onto the surface, forming a bonded sacrificial layer. This layer doesn't get squeezed out the way a liquid lubricant film does under extreme pressure — it's mechanically bonded to the metal. Even if the grease is entirely displaced, the MoS2 burnished layer continues to provide boundary lubrication.
There's a secondary consequence that matters for some applications: MoS2 works exceptionally well in vacuum. Unlike oil or grease, it doesn't evaporate or oxidise in the absence of oxygen — which is why it's used in spacecraft bearings and satellite mechanisms. In normal industrial use, this property translates to reliable performance in very slow-speed, high-load applications where hydrodynamic oil film formation is impossible.
Moly Grease vs Standard EP Grease: What's the Difference?
Extreme pressure (EP) grease and moly grease both handle high-load applications, but they work by completely different mechanisms — and they're not interchangeable.
Standard EP grease uses sulphur-phosphorus compounds as additives. Under boundary lubrication conditions — when metal surfaces are close enough to make asperity contact — these compounds react chemically with the metal surface at elevated temperature and pressure, forming iron sulphide or iron phosphide compounds. This sacrificial layer is softer than the base metal and wears away, preventing the harder metal from seizing.
The limitation: EP chemistry requires heat and pressure to trigger the reaction. In very slow-speed or oscillating applications — where there's no sliding velocity to generate heat — EP additives may not activate in time before metal-to-metal contact causes damage.
MoS2 doesn't wait for a chemical reaction. It forms a physical barrier regardless of speed or temperature. This makes moly grease specifically suited to:
- Slow-speed heavily loaded pivots (< 50 RPM)
- Oscillating or reciprocating motion where the lubrication film never fully develops
- Boundary lubrication conditions where metal surfaces are in near-contact
- Applications with severe shock loading where instantaneous pressure spikes exceed what EP chemistry can handle
Many premium moly greases contain both MoS2 and EP additives — the two mechanisms are complementary. The MoS2 covers the slow-speed boundary conditions; the EP chemistry handles the high-speed/high-temperature transitions. If you're specifying a moly grease for a mixed-duty application (e.g. a joint that oscillates slowly under load but occasionally sees faster motion), look for a product that includes both.
Quick comparison
| Property | Standard EP Grease | Moly Grease (MoS2) |
|---|---|---|
| Mechanism | Chemical reaction | Physical barrier |
| Works at slow speed? | Partially | Yes |
| Works under shock load? | Partially | Yes |
| Works at high speed? | Yes | No (becomes abrasive) |
| Sintered bearing safe? | Yes | No — never |
| Colour | Varies (often yellow/amber) | Dark grey to black |
| Staining risk | Low | High — permanent |
For a broader overview of grease types, NLGI grades, and thickener selection, see the Grease Selection Guide.
Moly Grease vs Moly Paste: Don't Confuse the Two
This is the most common moly-related mistake in Australian workshops, and it causes real equipment damage. Moly grease and moly paste are not the same product — and they're not interchangeable.
Moly grease contains 1–5% MoS2 by weight suspended in a conventional grease base. It's a lubricant designed for ongoing application in bearings, pivots, and joints.
Moly paste (also called molybdenum disulphide assembly paste) contains 25–70% MoS2 — a thick, high-concentration compound primarily designed for assembly, running-in, and anti-seize applications. Examples include Molykote G-n Plus, Rocol MTS 1000, and similar products.
| Property | Moly Grease (1–5% MoS2) | Moly Paste (25–70% MoS2) |
|---|---|---|
| MoS2 concentration | 1–5% | 25–70% |
| Consistency | Grease (NLGI 0–3) | Very thick paste |
| Primary use | Ongoing lubrication | Assembly, running-in, anti-seize |
| Applied via | Grease gun, brush | Brush, spatula |
| Interchangeable? | No. Different products for different purposes. | |
Moly paste applied as an ongoing bearing lubricant will pack the bearing with excess solid and cause premature failure. Moly grease used as an assembly compound won't provide sufficient MoS2 film for running-in protection. For anti-seize applications, see the Anti-Seize Compound Guide.
Where to Use Moly Grease: Applications
Moly grease performs at its best when three conditions converge: high load, slow or oscillating motion, and the risk of boundary lubrication conditions (where surfaces are close to metal-to-metal contact).
Mining and heavy construction equipment
Bucket pins, boom pivots, dipper arm pins, and slew ring bearings on excavators and loaders are the classic moly grease applications. These joints carry enormous loads, move slowly, and are subject to constant vibration and shock. Standard grease is squeezed out; moly grease — with its burnished MoS2 layer — maintains boundary protection even when the film thins.
Fifth wheel couplings
Truck and semi-trailer fifth wheels are one of the highest-volume moly grease applications in Australian transport. The coupling plate carries the full trailer load while articulating at low speed — exactly the boundary lubrication scenario where MoS2 excels. Most original equipment manufacturer (OEM) service manuals for fifth wheels specify moly grease explicitly.
Kingpins and leaf spring assemblies
Steering kingpins, leaf spring eyes, and shackle pins all operate at low speed under high static and dynamic load. MoS2 grease prevents fretting and galling in these joints. In AU agricultural equipment — headers, combines, and grader blades — kingpin lubrication with moly grease is standard practice.
Open gear and rack-and-pinion drives
Open gearing on cement kilns, ball mills, and large slewing drives typically runs at very low speed. Conventional grease flings off; EP grease may not adequately handle the combination of high tooth loading and slow pitch-line velocity. MoS2 open gear compounds provide the solid lubricant film that persists on the gear face between applications.
Splines, couplings, and sliding shafts
Splined driveshafts, telescoping shafts, and sliding couplings see relative motion only during adjustment or flexing — but can carry enormous torque. MoS2 grease prevents fretting corrosion (a common failure mode in splines under high torque, low-amplitude oscillation).
Wire rope lubrication (selected applications)
MoS2 wire rope lubricants are used on crane running ropes and mining haulage ropes where internal wire-on-wire friction is the primary wear mechanism. The MoS2 penetrates into the rope core and reduces internal wear — extending rope life in slow/cyclic applications.
High-load sliding surfaces and guides
Machine tool slideways, press ram guides, and heavy die-casting machine platens benefit from moly grease applied to sliding surfaces. The slow, heavily loaded reciprocating motion is an ideal MoS2 application.
Assembly and running-in (light moly concentration)
Some engineers apply a thin film of moly grease to machined surfaces during assembly of heavily loaded components — keyways, interference fits, and bearing seats — to prevent galling during initial assembly and to provide a protective film during the critical running-in period.
| Application | Why Moly? | Typical NLGI Grade |
|---|---|---|
| Excavator bucket/boom pins | High load, slow oscillation | 1–2 |
| Fifth wheel coupling | Full trailer load, slow articulation | 2 |
| Kingpin / leaf spring | Boundary lubrication under static load | 1–2 |
| Open gear / slew ring | Very low speed, very high load | 0–1 (fluid/semifluid) |
| Splines and sliding shafts | Fretting prevention under torque | 1–2 |
| Machine slideways | Slow reciprocating, high surface pressure | 1–2 |
| CV joints (appropriate type) | OEM specification, angular contact | 2 |
When NOT to Use Moly Grease
This section is the most important in the guide. Moly grease causes irreversible damage in several common applications. Know these before you reach for the black grease.
1. Sintered bronze (and iron) bearings — never, under any circumstances
Sintered metal bearings — the pressed-metal bushings used in small motors, power tools, domestic appliances, and light industrial equipment — are oil-impregnated by design. The porous sintered matrix acts as a reservoir: oil is drawn to the bearing surface by capillary action and heat, lubricating the shaft without any external grease.
MoS2 particles block those pores. The very fine MoS2 particles (1–5 microns) are the ideal size to lodge in and permanently clog the sintered matrix. Once the pores are blocked, the oil can no longer migrate to the bearing surface. The bearing overheats, seizes, and fails — and it cannot be repaired. The damage is irreversible.
2. High-speed rolling element bearings
At high DN values (shaft diameter in mm × RPM), the dynamics of a rolling bearing change. The elastohydrodynamic (EHD) oil film formed between rolling elements and raceways becomes very thin — typically 0.1–1 micron. MoS2 particles in standard moly grease are 1–5 microns. At sufficient speed, these particles are larger than the oil film they're supposed to supplement. They become abrasives, scoring the raceways and rolling elements.
As a general guide: if a bearing is running above 3,000 RPM or has a DN value above 100,000 mm·RPM, moly grease is almost certainly the wrong choice. Use a standard lithium complex or polyurea grease instead.
The exception: purpose-made high-speed moly greases with ultra-fine particle sizes (< 0.5 micron) exist for specific applications. These are specialist products — not standard off-the-shelf moly grease.
3. Wet and submerged environments
MoS2 is stable in water alone — the layers shed moisture without degrading. The problem is the combination of water, oxygen, and heat. Under sustained wet, oxidising conditions, MoS2 oxidises to molybdenum trioxide (MoO3) — a hard, abrasive compound — plus traces of sulphuric acid. The acid attacks metal surfaces and bearing steels. The MoO3 abrades them.
For occasional washdown or light moisture exposure, the risk is low. For submerged bearings, marine applications, or any joint that regularly sits in standing water, switch to a calcium sulphonate complex or lithium complex grease with proven water resistance.
4. Electrical contact applications
MoS2 is a semiconductor. In precision electrical contacts, slip rings, or current-carrying pivots, MoS2 grease can cause arcing, increased contact resistance, or short circuits. Use a purpose-made electrical contact grease or a fluorocarbon-based lubricant (e.g. PFPE/PTFE) in these applications.
5. Oxygen-rich or oxidising service
In compressed air or oxygen service — including breathing air compressors and oxygen equipment — MoS2 is not approved. Use only greases specifically approved for oxygen service (typically silicone or fluorocarbon-based).
Summary: when to avoid
| Application | Risk | Use Instead |
|---|---|---|
| Sintered bronze/iron bearings | Pore blockage — permanent failure | Plain mineral oil |
| High-speed rolling bearings (> 3,000 RPM) | Particle abrasion of raceways | Lithium complex or polyurea |
| Submerged / sustained wet | MoO3 formation — abrasion + acid | Calcium sulphonate complex |
| Electrical contacts | Semiconductivity — arcing | Electrical contact grease |
| Oxygen / compressed air service | Not approved — fire/explosion risk | PFPE / fluorocarbon grease |
Temperature Range and Limits
A common misconception: "MoS2 handles extreme temperatures, so moly grease is a high-temp lubricant." This is partly true and partly wrong, and the distinction matters.
MoS2 itself is thermally stable to approximately 350°C in air and above 1,100°C in vacuum or inert atmosphere. The MoS2 component of moly grease is not the temperature-limiting factor.
The grease base is the limiting factor. Standard lithium base moly grease operates continuously to about 120°C — the same upper limit as standard lithium grease. Short-term excursions to 150–180°C are generally survivable. Above that, the base grease degrades and the MoS2 is left behind as a dry film — which still provides some boundary protection, but is not an ongoing lubricant.
| Base Grease Type | Low Temp Limit | Continuous Temp Limit | Short-Term Peak |
|---|---|---|---|
| Lithium moly grease | -20°C | 120°C | 150°C |
| Lithium complex moly grease | -20°C | 150°C | 180°C |
| Synthetic (PAO) moly grease | -40°C | 160°C | 200°C |
| MoS2 (pure) | Stable to -270°C | 350°C (air), >1,100°C (vacuum) | N/A (solid) |
At the low end, standard lithium moly grease stiffens significantly below -20°C. Australian winter conditions in southern states and alpine areas — where overnight temperatures drop to -5°C to -15°C — are within range for standard moly grease. For cold-climate mining or construction operating at sustained sub-zero temperatures, use a synthetic base moly grease rated to -40°C.
Moly Grease and Water: Understanding the Limits
The relationship between moly grease and water is nuanced — and often misunderstood in both directions.
MoS2 by itself sheds water. The lamellar structure is hydrophobic — water doesn't penetrate the crystal layers. A burnished MoS2 film on a metal surface is effectively water-resistant. This leads some users to assume moly grease is suitable for wet applications.
The problem is oxidation, not water alone. When MoS2 is exposed to the combination of water, oxygen, and elevated temperature over sustained periods, a slow oxidation reaction occurs:
2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2
Molybdenum trioxide (MoO3) is a hard, white, abrasive powder — the opposite of what you want in a bearing. Sulphur dioxide dissolves in water to form sulphurous acid, which attacks ferrous metals and bearing steels. The combination of abrasive particles and acid is a reliable recipe for accelerated bearing failure.
How much water exposure is acceptable? For most Australian outdoor applications — occasional rain, washdown, humid conditions — the oxidation rate is slow enough that standard relubrication intervals prevent significant MoO3 accumulation. For joints that regularly sit in puddles, streams, or submerged in tanks, switch to a calcium sulphonate complex grease specifically formulated for wet service.
In Australian agriculture, mining, and marine applications where equipment operates in consistently wet conditions, the better choice is a calcium sulphonate or even a calcium complex grease with a high drop point. The lubrication hub guide covers the broader decision: Industrial Lubricants Guide.
Base Greases, NLGI Grades, and Compatibility
Moly grease comes in several base formulations and NLGI consistency grades. Understanding the difference helps you specify the right product for the application — and avoid compatibility problems when changing greases in service.
Base grease types
Lithium moly grease is the most common and widely available form. It covers the majority of industrial moly grease applications in Australian workshops and plant maintenance departments. It is compatible with most other lithium greases, making relubrication straightforward.
Lithium complex moly grease offers a higher dropping point (the temperature at which the grease loses its structure and becomes fluid) — typically above 260°C vs 180°C for standard lithium. This makes it suitable for wheel bearings, gearboxes, and applications that see sustained higher temperatures.
Synthetic base (PAO) moly grease is used where the temperature range extends below -20°C or above 150°C, or where extended relubrication intervals are required. Synthetic base oils have better viscosity stability across temperature extremes.
Calcium complex moly grease offers superior water resistance compared to lithium-based products. For Australian coastal or wet-industrial applications where moly grease is still appropriate (i.e. not submerged), calcium complex is worth considering.
NLGI consistency grades
NLGI (National Lubricating Grease Institute) grades measure grease consistency — essentially how stiff the grease is. The scale runs from NLGI 000 (almost fluid) to NLGI 6 (block grease). For most moly grease applications:
| NLGI Grade | Consistency | Typical Moly Applications |
|---|---|---|
| 0 | Semifluid | Open gears, slew rings, centralised lubrication systems, large slow joints |
| 1 | Soft | Bucket pins, boom pivots, kingpins, leaf spring eyes |
| 2 | Standard (most common) | Fifth wheels, splines, sliding guides, CV joints, general plant maintenance |
| 3 | Stiff | Vertical joints, high-vibration environments where grease retention is critical |
NLGI 2 covers the majority of moly grease applications in Australian industry. If the joint has a grease nipple and you're not sure what grade the original fill was, NLGI 2 is the safe default. For very large, slow, heavily loaded pivots — excavator bucket pins, slew rings — NLGI 1 often provides better penetration into the joint.
How to Apply Moly Grease Correctly
Application technique matters with moly grease — particularly around cleanliness, quantity, and staining management.
Preparation: clean the joint first
If converting a joint from a different grease type to moly grease, remove the old grease before applying. Incompatibility between greases is a real risk (see the mixing section below), and old contaminated grease dilutes the MoS2 concentration of the new grease. For bearing housings and grease-nipple joints, pump new moly grease through until old grease appears clean at the joint lip, then wipe the excess.
Quantity: more is not better
A common mistake with grease applications generally — and particularly with moly grease — is overpacking. A grease-packed rolling element bearing should be 1/3 to 1/2 full of grease. Overpacking causes the grease to churn, generates heat, and accelerates degradation. For sliding surfaces and pivot pins, a thin, even coating is all that's required.
Staining: plan for it
Moly grease stains everything it contacts dark grey to black. The staining is permanent on clothing and difficult to remove from skin. Standard practice:
- Wear nitrile or latex gloves — heavy-duty is better
- Keep moly grease away from painted surfaces where appearance matters
- Use a dedicated grease gun for moly grease — don't share with standard grease cartridges
- Any rags, towels, or disposable wipes used with moly grease will be permanently stained — factor this into waste management
Application by joint type
Grease nipples: Fit the grease gun coupler, pump slowly until new grease appears at the joint seal or lip. Wipe the excess. Don't pump against a blocked or seized nipple — you'll burst the seal.
Open joints and pins: Apply directly to the pin or bore surface, work through the full range of motion to distribute the grease, then wipe excess from the exterior. Excess grease on external surfaces attracts dirt, which becomes an abrasive contaminant.
Slideways and guides: Apply a thin smear by brush or gloved hand. Work the slideway through its full travel range to distribute. Re-apply per the equipment service interval.
Fifth wheel plates: Apply moly grease to the skid plate and king pin socket with a brush or spatula. The OEM service manual for most Australian semi-trailer fifth wheels specifies a thin, even coat rather than a heavy application.
Mixing Moly Grease with Other Greases
Grease compatibility is a critical maintenance topic that's frequently mishandled in practice. When two incompatible greases mix, the thickener structures can interact and collapse — converting solid grease into a fluid that runs out of the bearing, leaving no lubrication at all. This failure mode can happen gradually and is difficult to diagnose without knowing what greases were used.
Moly grease (typically lithium base) compatibility with common grease types:
| Adding Moly Grease (Lithium) to… | Compatibility | Action Required |
|---|---|---|
| Standard lithium grease | ✅ Generally compatible | Monitor — purge old grease if possible |
| Lithium complex grease | ✅ Generally compatible | Monitor — purge old grease if possible |
| Calcium complex grease | ⚠️ Borderline | Flush joint before switching |
| Polyurea grease | ❌ Incompatible | Full flush and clean before switching |
| Sodium (soda) grease | ⚠️ Borderline | Flush joint before switching |
| Bentone / clay grease | ⚠️ Borderline | Flush joint before switching |
In practice, many Australian workshop and field lubrication programs accept the risk of lithium-to-lithium-complex mixing in grease nipple applications — pumping the new grease through until the old grease is expelled at the joint. For sealed bearing housings or gearboxes where the old grease cannot be purged, flush the housing with clean compatible grease first.
The MoS2 particles themselves are inert and don't affect grease compatibility — it's the base thickener that determines whether two greases mix safely.
Choosing the Right Moly Grease
With the application and exclusion criteria established, selecting the right moly grease comes down to four decisions: base grease type, NLGI grade, MoS2 concentration, and whether EP additives are also required.
Decision guide
| Application Conditions | Recommended Type | Notes |
|---|---|---|
| General slow/heavy pivots, indoor, dry, ambient temp | Lithium moly, NLGI 2 | Most common off-the-shelf moly grease |
| Mining equipment, excavator pins, outdoor AU conditions | Lithium complex moly EP, NLGI 1–2 | EP additives cover any dynamic load spikes |
| Fifth wheel, kingpin, truck/trailer | Lithium complex moly, NLGI 2 | Check OEM spec — some mandate specific products |
| Cold-climate starts, extended intervals | Synthetic (PAO) moly, NLGI 1–2 | Superior low-temp flowability; longer service life |
| Open gearing, slew rings, large slow drives | Lithium or calcium moly, NLGI 0 | Semifluid penetrates large joints; resists throw-off |
| Intermittent high-load with some faster motion | Lithium complex moly + EP, NLGI 2 | Both mechanisms active |
| Service temp exceeds 120°C | Lithium complex or synthetic moly, NLGI 2 | Standard lithium base insufficient above 120°C |
MoS2 concentration
For standard industrial applications — the five listed in the "where to use" section — products with 3–5% MoS2 are appropriate. Higher concentrations (above 5%) are for extreme conditions and usually come in paste or semi-fluid form rather than standard grease. Concentrations below 3% are sometimes marketed as "moly-fortified" greases and provide some benefit, but less than a dedicated moly grease.
If you're not sure which product suits your application, AIMS Industrial's team can help you match the right moly grease to your equipment — call us on (02) 9773 0122 or contact us online.
Frequently Asked Questions
What is moly grease used for?
Moly grease is used for slow-speed, heavily loaded metal joints where a conventional grease film cannot maintain separation between surfaces. Common applications include excavator pins and bushes, fifth-wheel couplings, kingpins, mining equipment pivots, press-fit assemblies, and bolted joints subject to fretting. The MoS2 additive forms a physical barrier layer on metal surfaces, providing lubrication even when the grease itself is displaced.
What does MoS2 stand for?
MoS2 stands for molybdenum disulphide — a naturally occurring mineral with the chemical formula MoS2. It has a hexagonal layered crystal structure where sheets slide over each other under pressure with very low friction (coefficient approximately 0.025). MoS2 is milled to 1–5 micron particle size for use as a lubricant additive in greases and pastes.
What is the difference between moly grease and standard EP grease?
EP (extreme pressure) grease uses sulphur-phosphorus compounds that react chemically with metal surfaces at elevated temperature and pressure to form a sacrificial layer. This reaction requires heat to activate. Moly grease uses MoS2 particles that form a physical barrier regardless of speed or temperature — so it works in very slow or oscillating applications where EP chemistry may not activate in time. The two mechanisms are complementary; many industrial moly greases combine both MoS2 and EP additives.
Can I use moly grease on wheel bearings?
Generally no, not on modern automotive wheel bearings. Most modern passenger vehicle wheel bearings are sealed, pre-greased, and run at moderate-to-high speed — conditions where moly grease offers no advantage over standard lithium or lithium complex grease and where the MoS2 particles can interfere with the bearing's designed lubrication regime. For heavy truck wheel hubs and slow-moving agricultural equipment hubs, moly grease can be appropriate — but check the OEM specification first.
Is moly grease the same as anti-seize compound?
No — they are different products with different purposes. Moly grease contains 1–5% MoS2 in a conventional grease base and is a lubricant designed for ongoing relubrication of moving joints. Moly paste (or anti-seize compound) contains 25–70% MoS2 in a mineral oil or petrolatum carrier and is a one-time assembly compound for bolt threads and press-fit surfaces to prevent seizure. Anti-seize is not a grease and should not be used as ongoing lubricant in grease points.
Can moly grease be used on sintered bronze bearings?
No — this is a critical incompatibility. Sintered bronze (and sintered iron) bearings are oil-impregnated porous bushings designed to be self-lubricating. The pores are typically 10–35 microns in diameter; MoS2 particles are 1–5 microns and will permanently block these pores, destroying the bearing's ability to self-lubricate. The damage is irreversible and typically causes rapid failure of the bushing. Always use a light machine oil or manufacturer-specified oil on sintered bearings, never grease of any type.
What temperature can moly grease handle?
For most moly greases with a lithium base, the continuous service limit is 120°C — set by the grease base, not the MoS2. The MoS2 additive itself is stable to 350°C in air and above 1,100°C in vacuum or inert gas. For applications above 120°C, a lithium complex or synthetic (PAO) moly grease is required, extending the limit to 150–180°C depending on formulation. Above 180°C, solid lubricant paste or PTFE-based grease is typically more appropriate.
Can I mix moly grease with regular lithium grease?
Both lithium-based products are thickener-compatible in the sense that they won't immediately react or separate. However, mixing is still not recommended practice: it dilutes the MoS2 concentration below its effective level, you lose the known performance of each product, and it creates ambiguity about the lubrication specification in your equipment records. For a bearing or joint that should run on standard grease, flush and regrease properly rather than mixing.
Does moly grease work in wet or outdoor conditions?
Moly grease can be used in occasional wet or outdoor conditions, but sustained immersion or high-humidity applications reduce its effectiveness. When MoS2 is exposed to water and oxygen simultaneously over an extended period, it can slowly convert to molybdenum trioxide (MoO3), which is mildly abrasive. In normal outdoor Australian conditions — exposure to rain, washdown, morning condensation — a water-resistant moly grease with a suitable NLGI grade performs adequately. For continuous immersion or very high humidity, a calcium complex grease or NLGI 1–2 lithium complex without moly may be more suitable.
What is the difference between moly grease and moly paste?
Moly grease contains 1–5% MoS2 in a conventional grease base (usually lithium or lithium complex) and is used for ongoing lubrication of moving joints through a grease nipple or grease gun. Moly paste contains 25–70% MoS2 in a mineral oil or petrolatum carrier and is used as a one-time assembly compound on bolt threads, press-fit surfaces, and slip joints — the equivalent of anti-seize compound. They are not interchangeable: applying paste to a grease nipple provides far too much MoS2 and can generate abrasion at higher speeds, while grease provides insufficient MoS2 concentration for bolt thread protection.
Is moly grease suitable for CV joints?
Most CV joint greases are proprietary formulations — typically lithium complex or polyurea-based with PTFE or moly additives — specified by the OEM. For aftermarket CV joint repacking, a moly-fortified CV joint grease that meets the OEM specification is appropriate. Standard moly grease from a drum or cartridge is not ideal for CV joints, which run at variable speed and angle — the application requires a grease designed for the specific oscillating, high-load, variable-angle demands of a CV joint. Use a product labelled for CV joint applications.
What NLGI grade of moly grease should I use?
NLGI 2 is the most common grade for general industrial pivot and pin lubrication through a grease gun. NLGI 1 is appropriate for low-temperature applications, slow or heavily loaded pivots that need better penetration, and some grease-gun-fed centreline systems. NLGI 0 suits open gearing, slew rings, and large joints where the semifluid consistency allows better coverage. NLGI 3 is used for vertical joints or applications where the grease must resist slump. For most maintenance applications — excavator pins, kingpins, fifth wheels, industrial pivots — NLGI 2 lithium or lithium complex moly grease is the default.
Why does moly grease stain everything dark grey?
The dark grey colour is the MoS2 itself — molybdenum disulphide is naturally dark grey to near-black. The fine particle size (1–5 microns) means MoS2 penetrates skin lines and fabric fibres and is difficult to remove. This is not a defect; it is an inherent property of the additive. Wear nitrile gloves when working with moly grease. For skin: dish soap or workshop hand cleaner with pumice works better than standard soap. For clothing: treat immediately with pre-wash spray before washing — once set, MoS2 staining is generally permanent.
Is moly grease food grade?
Standard moly grease is not food grade and must never be used in food processing equipment where incidental product contact is possible. MoS2 itself is not approved under USDA H1 or NSF H1 classifications. Food-grade lubricants for bearings and joints in food processing environments use white mineral oil, PTFE, or synthetic (PAO) base oils with food-safe thickeners — none of which include MoS2. If you need a food-safe extreme pressure grease, look for NSF H1-registered products specifically.
How long does moly grease last before relubrication is needed?
Relubrication intervals for moly grease depend on load, speed, temperature, contamination exposure, and grease volume. As a general guide: excavator pins in heavy service need greasing every 8–50 hours (per OEM schedule); fifth-wheel couplings need greasing every service or 10,000–15,000 km; kingpins every 5,000–10,000 km or per OEM schedule; industrial pivots in ambient conditions every 250–500 operating hours. MoS2 extends useful life beyond standard grease in slow/high-load applications because the burnished layer persists after the base grease is displaced, but it does not eliminate the need for regular relubrication.
AIMS Industrial Moly Grease Range
AIMS stocks a range of moly greases for Australian industrial, plant maintenance, and heavy equipment applications. Our range covers standard lithium moly NLGI 2 for general applications through to lithium complex EP moly for high-load mining and construction environments.
Browse the full range at AIMS Greases & Lubrication Products, or contact our team to confirm the right grade for your specific equipment and service conditions. If you're comparing moly grease against standard EP or lithium complex greases for a new application, the Grease Selection Guide covers the full decision matrix including NLGI grades, thickener selection, and relubrication intervals.
For the broader lubrication picture — including hydraulic oil, gear oil, chain lubricants, and greases in context — see the Industrial Lubricants Guide. For linear bearings and sintered bushes (where moly grease must never be used), see the Linear Bearing Guide.
Our Sydney warehouse carries stock of moly grease products. Call (02) 9773 0122 or get in touch online — we're here to help.