ISO 46 vs AW 46 Hydraulic Oil: What the Two Labels Tell You

An ISO 46 R&O oil suits circuits whose components ask for no wear protection; AW 46, the same viscosity plus antiwear additives, suits vane and piston pumps. ISO 46 alone names only the viscosity grade, 41.4 to 50.6 mm²/s at 40 °C (ISO 3448:1992), so the pump data sheet decides which type is allowed.

• ISO 3448:1992, last confirmed in 2023, classifies industrial liquid lubricants by viscosity and says nothing about additives (ISO, 2023).

• ISO 11158:2023 covers five mineral oil categories, HH, HL, HM, HV and HG, and none of them is named AW (ISO 11158:2023).

• Rexroth accepts a fluid that meets only ISO 11158 HL, without proof that DIN 51524-1 is also met, only with its written approval (Bosch Rexroth RE 90220, 2012).

• The Vickers V series vane pump data sheet sets a preferred viscosity of 13 to 54 cSt at rated speed and pressure, so the operating temperature decides whether ISO VG 46 fits (Danfoss, 2024).

This comparison covers mineral oil hydraulic fluids in ISO VG 46 for hydrostatic systems in plants and mobile machines. It does not cover HV multigrade oils, fire-resistant fluids or environmentally acceptable fluids, which follow other standards.

How do ISO 46 and AW 46 hydraulic oil differ?

ISO 46 and AW 46 hydraulic oil differ in what the label promises: ISO 46 promises only a viscosity grade, while AW 46 promises that viscosity plus antiwear additives. An oil sold as R&O 46 is rust and oxidation (R&O) inhibited, which matches Class HL in ASTM D6158-23. An oil sold as AW 46 is meant to match Class HM, which adds anti-wear characteristics to HL (ASTM D6158-23).

The table below compares R&O 46 and AW 46 on the properties that decide which one a pump can use.

The row that matters is wear protection: both oils have the same viscosity, but only AW 46 carries antiwear additives and a pump wear test in its standard (Bosch Rexroth RE 90220, 2012).

Is AW 46 the same as ISO 46?

AW 46 is not the same as ISO 46: every AW 46 oil is an ISO 46 oil, but an ISO 46 oil is not necessarily antiwear. ISO 3448:1992, the viscosity classification, covers industrial liquid lubricants including hydraulic fluids and says nothing about additives (ISO 3448:1992). ISO says the 1992 edition was last reviewed and confirmed in 2023, so it remains current (ISO, 2023). The number 46 is the midpoint viscosity in mm²/s at 40 °C, and the grade spans 41.4 to 50.6 mm²/s (Anton Paar, 2026).

AW is a trade label, not a category in the standards. ISO 11158:2023 covers the mineral oil categories HH, HL, HM, HV and HG (ISO 11158:2023), and ASTM D6158-23 covers HH, HL, HM, HV, HMHP and HVHP (ASTM D6158-23). Neither list contains a category named AW. The AW label signals an antiwear oil, which the standards call HM or HLP, but the label alone proves nothing.

Read the technical data sheet instead. It should name a category and an edition, such as ISO 11158:2023 HM, DIN 51524-2:2017 HLP or ASTM D6158-23 HM, and show the wear test results. If it names only "AW 46", ask the supplier which of those standards the oil meets.

When is an R&O hydraulic oil without antiwear additives enough?

An R&O hydraulic oil without antiwear additives is enough only when every pump, motor and valve data sheet in the circuit allows HL oil and asks for no wear protection. Rexroth states that HL fluids "can be used in hydraulic systems that do not pose any requirements as to wear protection" and "may be used only for components whose product data sheet specifically allows HL fluids" (Bosch Rexroth RE 90220, 2012). It also tells users to observe restrictions as to pressure and rotation speed for HL (Bosch Rexroth RE 90220, 2012).

The standards draw the same line. DIN 51524-1:2017 applies HL oils to hydrostatic systems where thermal stress would shorten the life of oils without additives, or where water ingress could cause corrosion (DIN 51524-1:2017). DIN 51524-2:2017 applies HLP oils where antiwear additives for mixed friction are required in pumps or hydraulic motors "due to their design or operating conditions" (DIN 51524-2:2017).

In practice, R&O oil fits circuits that a maker has rated for it. Rexroth will accept fluids that meet only ISO 11158 HL, without proof that DIN 51524-1 is also met, only with its written approval (Bosch Rexroth RE 90220, 2012). Where the data sheet is silent or lists only HLP or HM, use AW oil.

Does AW 46 hydraulic oil work in vane and piston pumps?

AW 46 hydraulic oil works in vane and piston pumps, and it is the oil type many of their data sheets call for. Vane pumps "can suffer high rates of wear between the vanes and the cam ring if a suitable antiwear oil is not used" (STLE, 2016). The Vickers V series vane pump data sheet says to "Use antiwear industrial hydraulic oils" with viscosity grades of 32 to 68 cSt at 40 °C, for pumps that run at pressures to 207 bar (Danfoss, 2024).

Piston pumps follow the same pattern. The Rexroth A10VSO series 31 axial piston pump, rated at 280 bar nominal and 350 bar maximum, is designed for operation with HLP mineral oil according to DIN 51524-2 (Bosch Rexroth RE 92711, 2021). HLP is the DIN name for the antiwear type sold as AW.

The grade still has to fit the temperature. The same vane pump data sheet sets a preferred viscosity of 13 to 54 cSt at rated speed and pressure (Danfoss, 2024), so ISO VG 46 suits only the operating temperatures that keep it in that window. Check the viscosity window on each pump's data sheet before you choose between AW 32, 46 and 68.

How do you switch from R&O to AW hydraulic oil?

You switch from R&O to AW hydraulic oil by confirming the pump approval, checking compatibility with the old oil, then draining, flushing and refilling with filtered oil. Work in this order:

1. Confirm that every component data sheet lists HM or HLP oil in ISO VG 46.

2. Ask the AW oil supplier about compatibility with the remaining R&O oil. Rexroth recommends a written performance guarantee from the supplier of the new fluid and says the old fluid remaining should be minimized (Bosch Rexroth RE 90220, 2012).

3. Before draining, read both oils' safety data sheets (SDS), shut down, lock out and relieve stored hydraulic pressure under the site's energy control procedure, for example US OSHA 29 CFR 1910.147 (OSHA, 2026).

4. Drain the reservoir and lines. Rexroth treats a fluid with more than 2 % of another fluid as a mixture, and zinc-containing and zinc-free additive systems are most often incompatible (Bosch Rexroth RE 90220, 2012).

5. Change the filters and fill through a filter, because delivered oil usually does not meet component cleanliness levels (Bosch Rexroth RE 90220, 2012).

6. Store the drained oil in containers marked "Used Oil" where US 40 CFR Part 279 applies (eCFR, 2026), or under your local used oil rules.

7. Take an oil sample after the first hours of running to confirm viscosity and cleanliness.

What drives ISO 46 and AW 46 cost over the service life?

The cost of ISO 46 R&O and AW 46 oil over the service life is driven by pump wear, oil life, changeover work and the risk of mixing, more than by the oil itself. Pump wear comes first: vane pumps without a suitable antiwear oil can wear fast between vanes and cam ring (STLE, 2016), so pump protection is the first cost factor.

Oil life comes second, and it depends on temperature more than on the label. Above about 80 °C, fluid service life roughly halves for every 10 °C rise in reservoir temperature, a reference value for fluids with less than 0.1 % water (Bosch Rexroth RE 90220, 2012). A cooler and a clean reservoir help both oil types.

Changeover work comes third. Rexroth notes that changing the hydraulic medium at a later point "represents significant additional costs" (Bosch Rexroth RE 90220, 2012), so choose the right type at first fill.

Mixing risk comes last. A site that stocks both R&O 46 and AW 46 can top up the wrong one, and Rexroth does not generally permit mixing hydraulic fluids (Bosch Rexroth RE 90220, 2012). Comparing pump data sheets, oil data sheets and oil analysis history for this choice is the kind of case Lubinpla structures into one cited document for your review.

FAQ

Is HL 46 the same as R&O 46?

In most cases, yes. ASTM D6158-23 defines Class HL as a refined base oil with rust and oxidation inhibitors (ASTM D6158-23), which is what R&O means. HL also names the DIN 51524-1:2017 category. Check the data sheet, because R&O is a trade label and HL is a standard category.

Can you mix ISO 46 R&O and AW 46 hydraulic oil?

Avoid it. Rexroth does not generally permit mixing hydraulic fluids, even with the same classification, and counts more than 2 % of another fluid as a mixture (Bosch Rexroth RE 90220, 2012). If a top-up has already happened, ask both suppliers about compatibility and take an oil sample.

Can an R&O turbine oil 46 replace hydraulic oil?

Only after the pump maker confirms it. Rexroth allows turbine oils after confirmation, compares DIN 51515-1 turbine oils with HL, and notes they "usually offer lower wear protection than mineral oil HLP" (Bosch Rexroth RE 90220, 2012).

Working a case like this? Lubinpla works it from your own documents and site history, step by step with your approval. Free to start, no card.

Lubinpla does not sell chemical products and names no brands in recommendations. Our reviewer also leads a specialty chemicals distribution company.

Sources checked 2026-10-13.

Sources

1. ISO. ISO 3448:1992 Industrial liquid lubricants: ISO viscosity classification. Edition 2, 1992, confirmed 2023. https://committee.iso.org/standard/8774.html

2. Anton Paar. Viscosity of ISO Viscosity Classification: viscosity table (Anton Paar Wiki). Accessed 2026-10-13. https://wiki.anton-paar.com/en/iso-viscosity-classification/

3. ISO. ISO 11158:2023 Lubricants, industrial oils and related products (class L): Family H (hydraulic systems): Specifications for categories HH, HL, HM, HV and HG. Edition 3, 2023 (SIS catalog page). https://sis.se/en/produkter/petroleum-and-related-technologies/hydraulic-fluids/iso-111582023

4. ASTM International. ASTM D6158-23 Standard Specification for Mineral Hydraulic Oils. 2023. https://store.astm.org/d6158-23.html

5. DIN. DIN 51524-1:2017-06 Pressure fluids: Hydraulic oils: Part 1: HL hydraulic oils, minimum requirements. 2017. https://www.dinmedia.de/en/standard/din-51524-1/272262589

6. DIN. DIN 51524-2:2017-06 Pressure fluids: Hydraulic oils: Part 2: HLP hydraulic oils, minimum requirements. 2017. https://www.dinmedia.de/en/standard/din-51524-2/272262662

7. Bosch Rexroth. RE 90220/05.12, Hydraulic fluids based on mineral oils and related hydrocarbons. 2012 (edition read). https://hydraulique-martin.com/wp-content/uploads/2021/02/Bosch-Hydraulic-Fluid-Selection.pdf

8. Bosch Rexroth. RE 92711, Axial piston variable pump A10VSO series 31, data sheet. Edition 2021-05-17 (edition read). https://ahlsell.fi/external-assets/Documents/11/59/AssetDocument76541159.pdf

9. Danfoss. Vickers by Danfoss Vane Pumps, V Series Low Noise Vane Pumps, Technical Information BC443076030451en-000101. 2024. https://assets.danfoss.com/documents/latest/238665/BC443076030451en-000101.pdf

10. STLE (R. David Whitby). Selecting the correct hydraulic oil. Tribology and Lubrication Technology, January 2016. https://www.stle.org/images/pdf/STLE_ORG/BOK/LS/Hydraulics/Selecting%20the%20Correct%20Hydraulic%20Oil_Jan16%20tlt.pdf

11. US OSHA. 29 CFR 1910.147, The control of hazardous energy (lockout/tagout). Current text, accessed 2026-10-13. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.147

12. US eCFR. 40 CFR Part 279, Standards for the Management of Used Oil. Current text, accessed 2026-10-13. https://www.ecfr.gov/current/title-40/chapter-I/subchapter-I/part-279

Written by the Lubinpla team from the sources listed and checked against them before publication.