Hydraulic Oil ISO VG 32 vs 46 vs 68: Choosing Viscosity for UAE Heat

By the Lubesouq technical team · Last updated: 5 July 2026

ISO VG is the oil's viscosity in cSt at 40°C. In UAE heat, outdoor and heavy plant usually needs VG 46 or VG 68 — thinner VG 32 can drop below the pump's safe viscosity floor at summer operating temperatures. VG 32 belongs indoors: cooler, high-speed, precision systems. The OEM manual always wins.

What ISO VG actually means

ISO VG is the viscosity grade under ISO 3448, the international classification for industrial oils. The number is the oil's kinematic viscosity in centistokes (cSt) at 40°C, with a permitted band of ±10% around that midpoint. Each grade is roughly 50% more viscous than the one below.

The bands don't overlap. VG 32, 46, and 68 are genuinely different fluids, not marketing tiers.

ISO 3448 viscosity bands at 40°C
Grade	Midpoint (cSt)	Permitted range (cSt)
ISO VG 32	32	28.8 – 35.2
ISO VG 46	46	41.4 – 50.6
ISO VG 68	68	61.2 – 74.8

The pump doesn't care about the drum label

What a hydraulic pump needs is viscosity at its actual operating temperature. Bosch Rexroth's axial piston pump datasheets put the optimum efficiency window at 16–36 cSt, with an absolute short-term floor around 7–10 cSt. Eaton Vickers vane pump documentation asks you to stay within roughly 13–54 cSt at operating temperature.

Viscosity collapses as oil heats up. Shell's own datasheet for Tellus S2 MX 46 shows the same oil at 580 cSt at 0°C, 46 cSt at 40°C, and just 6.9 cSt at 100°C. The grade you pick decides where in the pump's window you sit at your real running temperature.

Why UAE heat pushes you up a grade

Here is the number that settles it. Per the Bosch Rexroth datasheet, an HLP 32 fill reaches the 10 cSt minimum-viscosity floor at about 73°C fluid temperature; HLP 46 doesn't hit it until about 85°C. One grade up buys roughly 10–12°C of safe operating headroom.

UAE summer ambient runs 40–50°C, and outdoor reservoirs settle well above ambient. That is exactly the margin a VG 32 fill doesn't have — and why general-purpose outdoor plant here runs VG 46, with VG 68 for heavy, continuous, high-load duty.

Heat also shortens oil life: by the Arrhenius rate rule, every 10°C rise in operating temperature roughly doubles the oxidation rate, halving the oil's service life. Running the right grade keeps temperatures — and oil bills — down.

Typical selection by application (OEM manual overrides)
Grade	Typical fit	Watch out for
ISO VG 32	Indoor, air-conditioned or cooler environments; high-speed precision hydraulics; machine tools, injection molding	Can run too thin in UAE summer outdoor service
ISO VG 46	The general-purpose default: excavators, loaders, presses, factory hydraulics	Verify cold-start flow on rare cold mornings — rarely an issue in the UAE
ISO VG 68	Heavy loads, continuous duty, sustained high temperature: large excavators, cranes, heavy presses	Too thick for high-speed, low-temperature systems — sluggish response, cavitation risk

Each grade up buys ≈10°C of headroom before the 10 cSt wear floor. VG 46 curve anchored to Shell Tellus S2 MX 46 TDS values; crossings match the Bosch Rexroth datasheet (73°C for HLP 32, 85°C for HLP 46).

What HM / HLP on the label means

HM (ISO 11158) and HLP (DIN 51524 Part 2) both designate anti-wear hydraulic oil — mineral oil with additives for oxidation resistance, rust protection, and anti-wear performance. They are equivalent classifications, and quality datasheets list both. Every hydraulic oil we stock in the ranges below is an HM/HLP anti-wear grade.

The cost of getting it wrong

Too thin: the oil film ruptures, metal touches metal, internal leakage past pump clearances rises, pressure and response drop, and the extra heat thins the oil further. Too thick: hard suction and cavitation risk, cold-start starvation, sluggish actuators, wasted energy.

And keep it clean — industry analysis attributes 70–80% of hydraulic system failures to fluid contamination, not mechanical defects. The right grade in a dirty system still fails.

Hydraulic oils in stock at Lubesouq

Every product below is live and in stock — prices in AED on the product page.

Frequently asked questions

Can I use VG 68 instead of VG 46?+

Often yes in hot, heavy-duty outdoor service — VG 68 holds more viscosity at high temperature. But check the OEM manual and the pump's viscosity window first: in a cooler or high-speed system VG 68 causes sluggish response and cavitation risk.

Is VG 46 or VG 68 better for an excavator in the UAE?+

VG 46 is the general-purpose default for mobile plant. Sustained summer duty under heavy load pushes many UAE operators to VG 68. If the machine runs hot and hard outdoors year-round, VG 68 has the safer margin; the OEM manual has the final word.

What does the 46 in ISO VG 46 mean?+

It's the oil's kinematic viscosity at 40°C: nominally 46 cSt, within an ISO 3448 band of 41.4–50.6 cSt. It is not a quality rating — just thickness at a reference temperature.

What's the difference between HLP 46 and HM 46?+

Nothing practical. HLP is the DIN 51524-2 designation and HM is the ISO 11158 designation for the same thing: anti-wear hydraulic oil. Datasheets usually list both.

Why does my hydraulic system run hotter in summer?+

Thinner oil at high temperature increases internal leakage and friction losses, which produce more heat — a self-reinforcing loop. If summer temperatures push your fluid below roughly 16 cSt at operating temperature, you're outside the pump's efficiency window and should consider the next grade up.

Sources

Facts in this guide were cross-checked against the following on 5 July 2026:

Not sure which grade fits your equipment? Message us on WhatsApp — +971 50 296 5485 — with the machine model and we'll answer honestly, even if the answer is "you don't need the expensive one."