DIN 51524-2 Explained: What HLP Hydraulic Oil Must Meet

This answer covers the German standard DIN 51524-2:2017-06 for new HLP oils at delivery. It does not set limits for oil in service, and it does not cover fire-resistant or environmentally acceptable fluids. Pump and valve makers often set stricter cleanliness limits than DIN 51524-2, so their approval lists decide the final choice.

What and whom does DIN 51524-2 cover?

DIN 51524-2 covers HLP hydraulic oils, the antiwear grade of the German hydraulic oil series, and it binds oil suppliers who claim the standard and buyers who specify it. As of 2026-10-14, DIN and DIN Media list DIN 51524-2:2017-06 as the current edition, published in German with an English translation (DIN Media, 2026). It replaced DIN 51524-2:2006-04 and its 2006-09 corrigendum (DIN Media, 2026).

The publisher's scope states that the standard "applies to the hydraulic oils listed in Table 1, for use predominantly in hydrostatic drive systems in which thermal stresses occur; where corrosion is expected as a result of the ingress of water; where oils containing anti-wear additives for mixed friction applications are required in pumps or hydraulic motors due to their design or operating conditions" (DIN 51524-2:2017-06, scope). The standard was prepared by DIN working committee NA 062-06-51 AA, Requirements for lubricating and other oils (DIN, 2026).

In practice the standard is a purchasing reference. Bosch Rexroth bases the use of mineral-oil hydraulic fluids in its components on compliance with the minimum requirements of DIN 51524 (Bosch Rexroth RE 90220, 2012), and Danfoss lists DIN 51524-2 as an accepted specification for mineral oil hydraulic fluids of category HLP (Danfoss 520L0463, 2016). A DIN 51524-2 claim on a data sheet is therefore what lets a fluid enter many approval lists.

What does DIN 51524-2 require?

DIN 51524-2 requires a new HLP oil to meet minimum values for wear protection, ageing, water separation, air release, filterability, corrosion, seal compatibility and cleanliness, with limits set per viscosity grade. OELCHECK summarizes the 2017 edition as defining "the minimum requirements for hydraulic oils in an unused condition with regard to water separation capacity, filter capacity, sealing compatibility, air separation capacity, oxidation stability and wear protection" (OELCHECK, 2026).

The table below shows each requirement, its test method and the limit where a public source confirms it; other limits are in the paid standard:

The row buyers check first is the FZG result: an HLP oil of ISO VG 32 or above must reach at least load stage 10 in the FZG test (OELCHECK, 2026; Bosch Rexroth RE 90220, 2012). The ISO VG 32 threshold and the air release figure come from a 2012 Rexroth summary written against the 2006 edition, so confirm them against the 2017 text. For viscosity, the public preview of part 1 lists DIN EN ISO 3104 among its normative references, and its foreword states that maximum viscosities at 0 °C or -20 °C and minimum viscosities at 100 °C are specified instead of a viscosity index (DIN 51524-1:2017-06, foreword). Where a row says the limit is in the standard, ask the supplier for the measured value and the limit it was judged against, grade by grade.

Which tests does an HLP oil have to pass?

An HLP oil has to pass two wear tests, an FZG gear rig test (ISO 14635-1) and a vane pump test (ISO 20763), plus the ageing, water, air, filterability and corrosion tests that DIN 51524-2 shares with the rest of the series (Bosch Rexroth RE 90220, 2012). The test conditions below come from that 2012 data sheet, written against the 2006 edition, so confirm them against the 2017 text.

The wear tests depend on viscosity grade. Bosch Rexroth notes that DIN 51524-2 and -3 prescribe at least FZG load stage 10 from ISO VG 32, and that the FZG test cannot be applied to viscosity classes below ISO VG 32 (Bosch Rexroth RE 90220, 2012). Rexroth also states that for ISO VG 10, 15 and 22, DIN 51524 defines no wear protection requirement (Bosch Rexroth RE 90220, 2012).

Filterability is tested on the new fluid and again after adding 0.2 percent water, under ISO 13357-1 and -2 (Bosch Rexroth RE 90220, 2012). The ISO 4263-1 TOST ageing test runs with 20 percent water (Bosch Rexroth RE 90220, 2012). Demulsibility under ISO 6614 is measured at 54 °C up to ISO VG 100 and at 82 °C above it (Bosch Rexroth RE 90220, 2012).

Rexroth notes that corrosion protection tests on different metals and alloys are described in DIN 51524 (Bosch Rexroth RE 90220, 2012), and the 2017 edition of part 1 lists the DIN EN ISO 2160 copper strip test among its normative references (DIN 51524-1:2017-06, clause 2).

How do you check that an oil really meets DIN 51524-2?

You check that an oil meets DIN 51524-2 by getting the supplier's test results for each required property at the exact viscosity grade you buy, then confirming batch cleanliness and water on delivery. A product data sheet that only names DIN 51524-2 is a claim, not evidence. For fluids classified to ISO 11158, DIN 51502 or ISO 6743-4, Rexroth requires conformity with DIN 51524 to be verified in the fluid's technical data sheet (Bosch Rexroth RE 90220, 2012).

Four checks cover most of the risk. First, confirm the claim names DIN 51524-2 and its edition, 2017-06, since the 2006-04 edition was replaced (DIN Media, 2026). Second, ask for the full test report per grade, including the FZG load stage and the vane pump result; FZG results are reported as scuffing load stages from 1 to 12 (OELCHECK, 2026). Third, test delivered oil for particle count and water: the minimum for new oil is cleanliness class 21/19/16 (OELCHECK, 2026) and a water content of at most 0.05 percent (ADDINOL, 2019). Fourth, compare the result with your equipment maker's limits, which are often tighter.

The standard applies at delivery, not in service. Rexroth points out that DIN 51524 "merely describes minimum requirements for hydraulic fluids in new condition at the time of filling into the bins" (Bosch Rexroth RE 90220, 2012). Oil in a running system is judged by condition monitoring limits, not by DIN 51524-2.

What is the difference between DIN 51524 parts 1, 2 and 3?

DIN 51524 part 1 covers HL oils with oxidation and corrosion protection, part 2 covers HLP oils that add verified wear protection, and part 3 covers HVLP oils that add improved viscosity-temperature behavior to HLP performance (Bosch Rexroth RE 90220, 2012). All three parts were issued as 2017-06 editions and are current as of 2026-10-14 (DIN Media, 2026).

The table below compares the three parts by oil type and the use each one targets:

The key row is part 2: an HLP oil is the default where pumps or motors run in mixed friction, as its scope states (DIN 51524-2:2017-06, scope).

The parts cross-refer. The 2017 part 1 scope states: "An oil as in DIN 51524-2 may be used where an HLP hydraulic oil is required for predominantly hydrostatic systems in which high thermal stresses arise and where corrosion is expected due to the ingress of water" (DIN 51524-1:2017-06, scope). Rexroth warns that HVLP viscosity may change in service through shear of the long-chain viscosity index improvers (Bosch Rexroth RE 90220, 2012).

Is DIN 51524-2 the same as ISO 11158 HM?

No, DIN 51524-2 and ISO 11158 HM are separate specifications for the same class of oil, so meeting one does not prove the other. ISO 11158:2023, edition 3, specifies minimum requirements for new mineral oil hydraulic fluids in categories HH, HL, HM, HV and HG (ISO 11158:2023, scope). HM is one of the categories named in the ISO 6743-4:2015 classification, and ISO 6743-4 itself sets no minimum requirements (Bosch Rexroth RE 90220, 2012).

Equipment makers treat the two as distinct. Danfoss lists DIN 51524-2 HLP and ISO 11158 HM as separate accepted specifications (Danfoss 520L0463, 2016). Rexroth allows ISO 11158 HL, HM and HV fluids without confirmation only when they are listed in the product data sheet and compliant with DIN 51524, and writes: "Fluids only classified in accordance with ISO 11158 may be used only with prior written approval of Bosch Rexroth AG" (Bosch Rexroth RE 90220, 2012).

Some data sheets claim both, and each claim rests on its own test program. When a component maker specifies DIN 51524-2, an ISO 11158 HM claim alone is not enough; ask the supplier to show DIN 51524-2 results as well. Where a maker accepts either, check which one its warranty terms name.

When should you call a specialist about DIN 51524-2 claims?

Call a hydraulics or lubricant specialist about a DIN 51524-2 claim when the supplier cannot show test results per grade, when the grade is below ISO VG 32, or when the component maker's limits differ from the standard. Each case means the paper claim may not match what the equipment needs.

Specific triggers are worth listing. A data sheet that cites DIN 51524-2 without an edition, or cites the replaced 2006-04 edition, needs clarification (DIN Media, 2026). A low-viscosity grade claimed as HLP needs a specialist view, because the FZG test cannot be applied below ISO VG 32 (Bosch Rexroth RE 90220, 2012, written against the 2006 edition). Servo valves and high-pressure systems usually need cleanliness well beyond 21/19/16; OELCHECK notes that this minimum "does not usually fulfil the requirements for servo valves and many other applications" (OELCHECK, 2026). A changeover between HLP products also deserves review: Rexroth reports that changeovers between fluids with zinc-containing and zinc-free additives frequently lead to malfunctions (Bosch Rexroth RE 90220, 2012).

A specialist can compare the supplier's results against the paid standard's limits and the component maker's approval list. Lubinpla works this kind of case from a site's own technical data sheets, certificates and maintenance history and returns one cited document for review.