How to choose grease for electric motor bearings by condition

This guide covers regreasable rolling bearings in industrial low voltage electric motors with bearings fitted for regreasing (grease nipple and outlet). It does not apply to sealed-for-life bearings, sleeve or oil-lubricated bearings, or bearings running above 110 °C (ABB, 2022), and where the motor maker names a grease, that instruction replaces the general rules here.

Which conditions decide the grease for electric motor bearings?

Five conditions decide the grease for electric motor bearings: the motor maker's specification, the mounting position, the bearing speed factor, the bearing temperature and the grease already in the bearing. The maker's specification comes first, because motor manuals tie relubrication intervals to the greases they list. ABB states for its low voltage motors that the intervals are based on its listed high-performance greases and that "Using other greases can reduce the interval" (ABB, 2022).

Mounting matters next. ABB halves the relubrication interval for vertical motors and recommends the stiffer end of its consistency range for them (ABB, 2022). Speed is expressed as a speed factor, the mean bearing diameter in mm multiplied by the speed in r/min; ABB requires a high-speed grease for 2-pole motors above a speed factor of 480,000 (ABB, 2022).

Temperature shortens grease life. ExxonMobil reports that grease oxidation rate doubles for every 10 °C rise above 49 °C (ExxonMobil, 2023), and ABB's grease specification holds only for bearing temperatures below 110 °C (ABB, 2022). The grease already in the motor limits any change, because greases with different thickeners should, with some exceptions, be considered incompatible (ExxonMobil, 2023). Record all five conditions for each motor before choosing a grease.

Which grease types fit electric motor bearings?

Polyurea and lithium complex greases without extreme pressure (EP) additives are the two grease types that fit most electric motor bearings; other types fit only special conditions. The table below sorts the common grease types by fit for a regreasable motor bearing.

The key row for most horizontal motors is lithium complex or polyurea: both reach dropping points of about 260 °C or higher (ExxonMobil, 2023), and ABB's specification for lithium complex grease calls for base oil of 100-160 mm2/s at 40 °C (ABB, 2022). Mineral base oils are adequate for most electric motor bearings, while synthetic base oils may be needed for extreme temperatures or longer regreasing intervals (ExxonMobil, 2023). Simple lithium greases and other soap types appear in some motor maker lists; check the maker's list rather than assuming they fit. A grease sold for motors should state its thickener, base oil type and base oil viscosity on its technical data sheet; without those three values the type cannot be matched to this table.

Electric motor grease choice by mounting, speed and temperature

Electric motor grease choice by mounting, speed and temperature follows the decision table below, and each row starts from the conditions you can read on the motor nameplate, the drawing or a temperature check. The table decides thickener, base oil viscosity and NLGI grade for one bearing. Read it from the top and stop at the first row that matches: a maker listing overrides every later row, and a speed, temperature or thrust row overrides the general horizontal row.

The row that applies to most motors is the second: a horizontal motor below a speed factor of 480,000 and a bearing temperature of 110 °C takes an NLGI 2 lithium complex grease with base oil of 100-160 mm2/s at 40 °C, as ABB specifies (ABB, 2022), or an NLGI 2 polyurea motor grease the maker accepts. Before any switch of thickener, check compatibility with the grease in the bearing using ASTM D6185-24, Standard Practice for Evaluating Compatibility of Binary Mixtures of Lubricating Greases (ASTM International, 2024), and purge as much old grease as possible (ExxonMobil, 2023).

Is electric motor grease different from general bearing grease?

Electric motor grease differs from general bearing grease mainly in additives, oxidation life and shear stability, not in thickener family. ExxonMobil advises that, unless a motor is mounted so there is a thrust load on the bearings, "it is generally advisable to use a grease without extreme pressure (EP) additives" (ExxonMobil, 2023). ABB states that in general lubricants containing EP admixtures are not recommended for its motor bearings and that their use must be evaluated case by case with the lubricant supplier (ABB, 2022). A general-purpose EP bearing grease can therefore be the wrong choice for a motor even when its thickener and grade match; that is our reading of both sources.

Oxidation life matters because motor bearings often run hot and continuously for long intervals. ExxonMobil recommends choosing a grease with a high ASTM D3336 oxidation life (ExxonMobil, 2023). ASTM D3336-26, Standard Test Method for Life of Lubricating Greases in Ball Bearings at Elevated Temperatures, evaluates grease performance in ball bearings "operating under light loads at high speeds and elevated temperatures" (ASTM International, 2026).

Shear stability is the third difference. An electric motor bearing grease should soften no more than 1 to 1.5 NLGI grades after 100,000 strokes in the ASTM D217 test, because a grease that softens more may leak out of the bearing with age (ExxonMobil, 2023).

Why is polyurea grease common in electric motor bearings?

Polyurea grease is common in electric motor bearings because it combines a high dropping point with long life in sealed and long-interval bearings, and motor makers list it. ExxonMobil describes polyurea as "A thickener increasingly employed in electric motor bearing lubrication" and gives polyurea and lithium complex greases dropping points of approximately 260 °C or higher (ExxonMobil, 2023). In a 2022 feature by the Society of Tribologists and Lubrication Engineers (STLE) quoting grease formulators, one formulator said that for electric motor and other fill-for-life applications, "polyurea-based greases seem to be the preferred choice", while suitably modified lithium greases may still be used (STLE TLT, 2022).

Supplier data show what a motor polyurea grease looks like. One mineral oil polyurea series for electric motors lists base oil of 115 mm2/s at 40 °C in NLGI 2 and NLGI 3 grades (ExxonMobil, 2026), and a synthetic series lists 85 mm2/s at 40 °C (ExxonMobil, 2026). These are single product families, not a rule for all polyurea greases.

Polyurea is not the only correct answer. ABB's base specification for its low voltage motors is lithium complex grease, and ABB lists polyurea greases for high-speed cast iron motors with the condition that they are "not mixed with lithium complex greases" (ABB, 2022). A motor that runs on lithium complex grease should stay on it unless a compatibility test supports the change.

Which NLGI grade suits horizontal and vertical motors?

NLGI 2 suits most horizontal electric motors, and NLGI 3 suits vertical motors, very large motors and hot-running bearings. The NLGI grade is set by worked penetration in ASTM D217-21a: NLGI 2 covers 265 to 295 tenths of a millimetre at 25 °C and NLGI 3 covers 220 to 250, so a lower number means a stiffer grease (ASTM D217-21a, 2021).

ExxonMobil reports that NLGI 2 is the most commonly used grade in electric motor applications (ExxonMobil, 2023). ABB accepts NLGI 1.5 to 3 for its low voltage motors and states: "A stiffer end of scale is recommended for vertical mounted motors or in hot conditions." (ABB, 2022). Supplier data follow the same split: an NLGI 3 polyurea motor grease is "more specifically recommended for applications such as vertically mounted bearings, or very large motors where a stiffer grease consistency may be required by the OEM" (ExxonMobil, 2026).

Consistency also affects how the grease moves. A grease's consistency affects pumpability and its ability to reach the areas to be lubricated (ExxonMobil, 2023), so an automatic lubrication system may limit the grade; ABB states that the grease used with automatic lubrication should be suitable for it (ABB, 2022). Vertical motors also need more frequent regreasing: ABB halves the interval for vertical motors whatever the grade (ABB, 2022).

What should you ask your supplier about electric motor grease?

Ask your supplier for the grease properties that match the conditions in the decision table, each with its test method, and confirm them on the technical data sheet (TDS) for the exact grade. Seven questions cover most motor bearings.

First, which thickener and base oil type the grease uses, and whether it contains EP additives. Second, the base oil viscosity at 40 °C by ASTM D445, to compare with the motor maker's range, such as ABB's 100-160 mm2/s (ABB, 2022). Third, the NLGI grade and worked penetration by ASTM D217-21a (ASTM D217-21a, 2021). Fourth, the change in penetration from 60 to 100,000 strokes, which shows shear stability; one motor grease data sheet lists a change of 40 tenths of a millimetre (ExxonMobil, 2026). Fifth, the dropping point and the ASTM D3336 high-temperature life, with the test temperature stated (ExxonMobil, 2023).

Sixth, which compatibility data the supplier holds against the grease now in your motors, and whether it was produced by the methodology of ASTM D6185 (ExxonMobil, 2026). Seventh, whether the motor maker lists or accepts the grease, since ABB bases its relubrication intervals on its listed greases (ABB, 2022). A supplier that cannot answer the compatibility question for your existing grease leaves you to purge and test before the change.

When should you call a lubrication specialist about electric motor grease?

Call a lubrication specialist about electric motor grease when the motor falls outside the standard conditions in the decision table or when grease changes keep failing. Four cases justify outside help. The bearing runs above 110 °C, a limit ABB says "must not be exceeded" for grease and bearings, so the cause of the heat needs finding before any grease change (ABB, 2022); or the ambient is outside -30 to +55 °C, where ABB's own specification asks users to consult ABB (ABB, 2022). The motor is a high-speed 2-pole unit above a speed factor of 480,000 (ABB, 2022), or runs at higher speed on a frequency converter, which ABB says requires shorter lubrication intervals (ABB, 2022).

The third case is unknown or mixed grease in the bearing. With some exceptions, greases with different thickeners should be considered incompatible; incompatible greases usually soften or become fluid but can also stiffen, and both can cause a lack of lubrication (ExxonMobil, 2023). The fourth is repeated bearing failure or hot bearings after regreasing, because over-lubrication can also lead to bearing failure and migration of lubricant into the windings (ExxonMobil, 2023).

A specialist should see the motor data sheet, the grease TDS and safety data sheet (SDS), the regreasing records and any bearing temperature trend. Lubinpla, an applied AI company, works a case like this from your own documents, such as the TDS and SDS, and site history, and returns one cited document for your review, with each step approved by you.