Hydraulic Oil HM vs HV vs HVLP — Choose the Right Type, Not Just the Viscosity Grade

You picked the right viscosity grade — ISO VG 46, exactly as the machine manual specifies — and the pump still wears out faster than it should, seals leak, the servo valve sticks. The cause technicians most often miss: "right grade, wrong type." The same ISO VG 46 hydraulic oil comes in several types (HL, HM, HV, HVLP) that behave completely differently. This guide covers how to choose the right type — the step everyone skips after picking the grade.

Not sure about the viscosity grade yet? Read alongside Hydraulic Oil ISO VG 32/46/68 — how they differ and selecting by pump type and machinery.

Viscosity Grade ≠ Oil Type

The ISO VG number (32/46/68) only tells you "how thick at 40°C" — one dimension. An equally important dimension is the type, which defines the additive package: anti-wear agents, VI improvers, anti-foam, anti-rust. Two drums of VG 46 with identical viscosity — one HL, one HV — protect the pump very differently.

The standards that classify "type" are ISO 6743-4 (Family H for hydraulic systems) and, on the German side, DIN 51524.

The Letter Codes (ISO 6743-4) — read the label

Code	Name	Key additives	Use for
HH	Plain mineral	None	Obsolete — no rust/oxidation inhibitors
HL	R&O oil	Rust + oxidation inhibitors	Low-pressure systems, no high-pressure pump
HM	Anti-wear (AW)	HL + anti-wear	Gear/vane/piston pumps under pressure — the plant standard
HR	HL + VI improved	Inhibitors + VI improver	Low-pressure, swinging temperature
HV	High-VI AW	HM + VI improver	Outdoor / wide temp swing + high pressure
HG	AW + anti-stick-slip	HM + anti-judder	Combined hydraulic + slideway systems
HS	Synthetic	Synthetic base	Extreme temperatures (not fire-resistant)

On DIN 51524 labels (common on European products):

• HL = DIN 51524-1 (equivalent to HL)
• HLP = DIN 51524-2 (equivalent to HM — anti-wear) ← the most common grade
• HVLP = DIN 51524-3 (equivalent to HV — high-VI anti-wear + low pour point)

Easy rule: HLP = HM, HVLP = HV — same fluid, different standard naming. If the manual says HLP 46, an HM ISO VG 46 oil is the correct match.

The Three Types You Actually Choose Between: HL vs HM vs HV

In practice the decision comes down to these three:

Property	HL (R&O)	HM / HLP (anti-wear)	HV / HVLP (high-VI AW)
Anti-wear additive (AW/ZDDP)	❌ None	✅ Yes	✅ Yes
Typical Viscosity Index (VI)	~95–105	~95–105	~140–180
Pressure capability	Low (≤70 bar)	High (≥250 bar)	High (≥250 bar)
Operating temperature window	Narrow	Moderate	Wide
Cold start / outdoor work	Fair	Fair	Excellent
Price/litre (approx.)	Lowest	Mid	~10–25% above HM
Typical use	Low-pressure lube systems	General factory pumps	Forklifts/excavators/outdoor gear

Bottom line: HL has no anti-wear additive — never use it on high-pressure pumps (vane/piston). HM and HV protect against wear equally; they differ in how stable the viscosity stays as temperature changes.

Viscosity Index (VI): the heart of HM vs HV

VI measures "how much viscosity changes with temperature" — higher VI = more stable viscosity. A typical HM oil is VI ~100; HV/HVLP is VI ~150+.

Why it matters — a system that starts cold at 15°C in the morning and runs until the oil hits 70°C:

• HM (VI 100): very thick when cold, the pump strains to draw it (cavitation risk); thins out fast when hot, the film may run short.
• HV (VI 150+): cold and hot viscosity stay much closer — smooth from cold start, and holds the film when hot.

flowchart TD
  A["Does this system see a wide temp swing?
(cool morning↔hot afternoon, or outdoor)"]
  A -->|"Small swing
indoor, climate-controlled"| B["HM / HLP
(VI ~100) is enough"]
  A -->|"Wide swing
outdoor/mobile"| C["HV / HVLP
(VI 140-180)"]
  B --> D{"System pressure?"}
  D -->|"≤70 bar, no AW pump"| E["Consider HL
(economical)"]
  D -->|">70 bar, has a pump"| F["HM for sure
needs anti-wear"]
  C --> G{"Near a heat source/
flame?"}
  G -->|"Yes"| H["Look at fire-resistant
ISO 12922 (HFC/HFDU)"]
  G -->|"No"| I["Standard HV"]

When the HV (high-VI) premium is worth it

HV/HVLP costs ~10–25% more than HM — pay the premium when:

• Equipment is outdoor or in a non-air-conditioned plant where temperature swings tens of degrees a day
• Equipment is mobile: forklifts, excavators, cranes, truck-mounted hydraulics
• You want to cut cold-start wear on an expensive pump
• A servo system needs consistent response all day long

For an indoor factory pump at a fairly stable 25–40°C → HM is enough; don't pay the premium.

Want the real numbers on how switching type/brand changes your annual cost? Enter your machine count + change interval in the Annual Lubricant TCO Calculator — free, instant figures.

Zinc-free / ashless oils: when you need them

Most HM/HV oils use zinc-based anti-wear (ZDDP), which is effective and inexpensive. Some applications need ashless (zinc-free):

• Newer servo-valve systems sensitive to zinc deposits
• Systems with lots of yellow metals (brass/bronze) — some ZDDP formulations attack yellow metal
• Applications emphasizing environmental safety or with water-contamination risk

Not every system needs ashless — standard ZDDP is usually better and more economical. Choose ashless only when the machine/valve maker specifies it.

Near heat or flame — you need fire-resistant fluid (ISO 12922)

In foundries, die-casting, furnaces, and steel rolling mills where a hydraulic line could rupture near a heat source, mineral oil can ignite. Use a fire-resistant fluid per ISO 12922:

Type	Base	Character
HFC	Water-glycol	Good fire resistance, economical, but limited pressure/temperature
HFDU	Synthetic ester (water-free)	Fire-resistant + near mineral-oil performance + biodegradable
HFDR	Phosphate ester	Highest fire resistance, specialized applications

⚠️ Switching from mineral oil to a fire-resistant fluid is not just a drain-and-fill — you must check seal, paint, and pump compatibility and may need a system flush. Always consult an engineer first.

OEM approvals that matter on the label

Don't read just "HM 46" — look for the pump-maker approvals the oil actually passed, because each runs real-pump wear tests:

• Denison HF-0 (Parker) — the most stringent, combining HF-1 (anti-wear) + HF-2 (filterability + water tolerance). HF-0 means it covers both.
• Eaton (Vickers) 35VQ25 / M-2950-S / I-286-S — vane-pump tests for heavy-duty / mobile use
• Bosch Rexroth RE 90220 / RDE 90235 — German criteria for high-pressure piston pumps
• Cincinnati Machine P-68/P-69/P-70 — classic criteria for VG 32/68/46

An oil carrying Denison HF-0 + Eaton + Rexroth works with nearly every pump brand on a Thai factory floor.

Hydraulic oils Sahawatthanakit supplies

SK ZIC HYDRO Series (Korean VHVI synthetic base — anti-wear / HM):

• ZIC HYDRO 32 / 46 / 68 — DIN 51524 Part 2 (HM/HLP), ISO 11158 HM, Denison HF-0, Eaton (Vickers) 694 / I-286-S, Bosch Rexroth RE 90220

Need HV/HVLP (high-VI) for outdoor/mobile gear, or fire-resistant fluid for work near heat? Send the machine model + the spec from the manual and our engineers will source the exact match.

Pack sizes: 1L · 4L · 18L pail · 200L drum — company delivery across Greater Bangkok, private freight upcountry.

Frequently Asked Questions

If the manual specifies HLP 46, can I use HM ISO VG 46 instead? Yes — HLP (DIN 51524-2) is the same type as HM under ISO 6743-4, just named under a different standard. As long as the viscosity grade (VG 46) and the pump-maker approvals match, it is the correct substitute.

Is the only difference between HM and HV the VI? Essentially yes — both are anti-wear oils. HV simply has a higher Viscosity Index (~140–180 vs HM's ~95–105), so its viscosity changes less with temperature, making it suited to wide temperature swings or outdoor work.

Can I mix HM and HV from different brands? Not recommended — different additive packages can clash, forming deposits or losing anti-wear performance. To change type/brand, drain the old oil completely and flush the system.

Should I just use HV everywhere to be safe? You can in terms of protection (HV is equally anti-wear), but you pay more for no benefit if the system is indoors at a stable temperature — wasted budget.

Is the ZDDP (zinc) in HM oil a problem for my machine? Usually not — ZDDP is the standard, effective, most economical anti-wear additive. The exceptions are some newer servo systems or yellow-metal-heavy systems where the maker specifies ashless (zinc-free).

Order & enquire

Send your machine model / pump brand / manual spec (HM, HV, HLP, HVLP, required approvals) and our engineers will match type + grade + approval before you order.

• Phone: 02-096-2118 / 061-541-6939 / 096-109-4244 (Khun Mam)
• LINE: @406rrgvm
• Email: info@sahawatthanakit1988.com
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