Grease NLGI Grade and Base Oil Basics
Grease choice depends on consistency, thickener, base oil viscosity, temperature, load, speed, water, contamination, and compatibility.
In this guide
Why is NLGI grade not a grease specification?
Use this guide for bearings, conveyors, crushers, pumps, motors, screen exciters, and wet or dusty equipment.
NLGI grade describes consistency, not the whole lubricant. Base oil viscosity carries film strength. Thickener chemistry affects compatibility. EP additives help high-load points.
What should drive grease selection?
Match the OEM requirement first, then check load, speed, temperature, water washout, contamination, relube interval, and whether the old grease is compatible.
Treat NLGI as the consistency clue, not the full answer. Two NLGI 2 greases can differ in base oil viscosity, thickener chemistry, EP package, water washout, temperature behavior, oxidation resistance, and compatibility with the grease already in the bearing.
Match the OEM requirement first. Then check load, speed, temperature, water, dust, washdown, contamination, relube interval, relube amount, and whether the old grease is known or unknown. If the old grease is unknown, compatibility is unknown too. Related GO4FORGE paths include lubricants, grease cartridges, PM schedules, bearings, conveyors, crushers, pumps, and maintenance planner parts.
What lubrication context belongs in the RFQ?
Send equipment model, bearing type, speed, temperature, load, environment, current grease, relube interval, and failure mode.
Send the equipment model, bearing type, speed, temperature, load, environment, current grease if known, relube interval, relube amount, failure mode, and whether the application is motor bearing, slow heavy bearing, wet conveyor, crusher, pump, or screen drive.
The request should also say what problem is being solved: heat, noise, vibration, washout, contamination, grease separation, short bearing life, or PM confusion. Boundary: Do not mix incompatible greases or override OEM lubrication requirements without qualified review.
What does NLGI grade not tell me?
NLGI describes grease consistency; it does not fully describe base oil viscosity, thickener chemistry, additives, compatibility, or relube interval.
A grease can be the same NLGI grade and still behave differently in a bearing. NLGI is the stiffness or consistency of the grease. The base oil supplies the lubricating film. The thickener holds the oil and affects compatibility. Additives handle load, oxidation, rust, tack, and other service needs.
That means "NLGI 2" is not a full specification. A better refill request includes:
| Field | Why it matters |
|---|---|
| OEM recommendation | Sets the baseline requirement |
| Base oil viscosity | Helps match speed, load, and temperature |
| Thickener type | Controls compatibility with existing grease |
| EP or non-EP need | Separates high-load points from motor bearings or lighter service |
| Water, dust, heat, or washdown exposure | Changes washout, contamination, and oxidation behavior |
| Relube interval and amount | Prevents undergreasing and overgreasing |
If the existing grease is unknown, treat compatibility as unknown. Mixing incompatible greases can soften, harden, bleed, or starve the bearing.
What lubrication mistakes show up in maintenance work?
The common mistakes are mixing incompatible grease, using consistency as the whole spec, ignoring contamination, and overgreasing bearings.
More grease is not always more protection. Bearings can run hot when excess grease churns, seals can be damaged by pressure, and contamination can be pushed around instead of removed. The better habit is to tie lubrication to condition: temperature, noise, vibration, ultrasound trend, leakage, washdown, dust, and the last known lubricant.
For recurring bearing failures, the grease may not be the only cause. Check alignment, fit, seal condition, contamination, belt tension, speed, load, relube volume, and the PM interval. A lubrication guide should help ask those questions before the site buys another case of the same grease and repeats the same failure.
What should happen before changing grease families?
A grease change should account for compatibility, purge method, relube amount, condition symptoms, and the reason the old grease failed.
Changing grease is not just buying a better tube. If the old and new thickeners are incompatible, the mixture can soften, harden, bleed oil, or starve the contact. If the relube amount is wrong, the bearing can run hot from churning or dry from too little film. If contamination or alignment is the true cause, the new grease inherits the old failure.
Before changing families, record the current product if known, purge plan, bearing temperature, noise, vibration, seal condition, environment, and what the change is expected to fix. A grease choice should leave a PM note, not just a different cartridge on the shelf.
Frequently Asked Questions
Where does the repair begin?
Match the OEM requirement first, then check load, speed, temperature, water washout, contamination, relube interval, and whether the old grease is compatible.
What should travel with the RFQ?
Send equipment model, bearing type, speed, temperature, load, environment, current grease, relube interval, and failure mode.
Where does convenience become risk?
Do not mix incompatible greases or override OEM lubrication requirements without qualified review.
Sources and Review Boundaries
Published by GO4FORGE. Editorial method. These notes help narrow sourcing evidence and selection risk; they do not replace the responsible site authority, OEM procedure, code requirement, or qualified engineering/safety review.
- GO4FORGE product knowledge files Internal product-knowledge references distilled into public decision guides.
- GO4FORGE RFQ evidence model Shop-floor evidence patterns for quotes, substitutions, and sourcing review.
- SAE J429: mechanical and material requirements for inch fasteners
- ASTM A563: carbon and alloy steel nuts
- ASTM F3125: high-strength structural bolts
- ASTM F1941/F1941M: electrodeposited coatings on mechanical fasteners
- IFI Fastener Standards reference family
- NLGI grease consistency reference
- ASTM D217 grease penetration test reference
- ISO 3448 viscosity grade reference
- OEM bearing, belt, and lubrication manuals