ISO Viscosity Grade (VG) — What the Number Means

ISO VG is a single-number viscosity classification at 40°C. Higher numbers = thicker oil at operating temperature. Common hydraulic grades:

ISO VG Grade	Viscosity at 40°C (cSt)	Typical Application
VG 32 (AW32)	28.8–35.2	Light-duty systems, machine tools, indoor equipment
VG 46 (AW46)	41.4–50.6	General construction, cranes, forklifts — most common in SG
VG 68 (AW68)	61.2–74.8	High-load or high-ambient-temperature systems, slow-speed circuits
VG 100	90–110	Very slow-speed large cylinders, tropical pressing equipment

AW46 vs AW68 for Singapore Conditions

AW46 is the default choice for most Singapore construction and industrial equipment operating in air-conditioned machine rooms or in open-air conditions where the system has good cooling. It provides lower drag, faster response, and better cold-start behaviour (even though Singapore rarely drops below 24°C).

AW68 is the right choice when:

• The hydraulic system operates continuously in sustained tropical heat (outdoor equipment running long shifts)
• High system pressure (>250 bar) causes significant heat generation
• OEM explicitly specifies VG 68 in the service manual
• The equipment has been running AW46 with a history of overheating faults

Bottom line: most cranes, excavators, and loaders operating in Singapore perform well on AW46. Switch to AW68 only if you have evidence of thermal issues or the OEM specifies it.

Hydraulic Fluid Contamination — The Main Failure Mode

Hydraulic system failures in Singapore are overwhelmingly caused by contamination, not wrong viscosity selection. Key contamination sources:

• Water ingress — breathers saturated by humidity; condensation from temperature cycling; flooded reservoir on a wet worksite
• Particulates — worn pump/valve debris; contaminated refill; damaged seals
• Oxidation products — extended drain intervals in hot systems produce varnish and sludge that block servo valves

Use a 10-micron return filter as a minimum. Replace breather desiccants every 6 months in Singapore humidity. Change oil by colour and particle count, not just hours — milky appearance means water contamination requiring immediate draining.

Change Intervals

OEM-specified intervals assume controlled conditions. In Singapore’s heat and humidity:

• Mineral AW46/68: change every 2,000 hours or annually (whichever first)
• Semi-synthetic: 3,000–4,000 hours with oil analysis
• Full synthetic: up to 6,000 hours — only viable if contamination control is excellent

Always flush and clean the reservoir when changing oil type or after a contamination event.

Related Guides