Hydraulic Oil ISO VG 46 vs 68: How to Choose the Correct Grade
ISO VG 46 and ISO VG 68 describe viscosity ranges at 40°C. ISO VG 68 is thicker at the same temperature, but it is not a higher quality level. The correct grade is the one specified for the pump, clearances, load and operating-temperature range.
ISO VG 46 and 68 compared
| Item | ISO VG 46 | ISO VG 68 |
|---|---|---|
| Nominal viscosity class at 40°C | 46 | 68 |
| Relative thickness at the same temperature | Lower | Higher |
| Quality ranking? | No | No |
| Correct use | Only where the equipment manufacturer permits the grade and performance type | |
Official Mobil Hydraulic AW data illustrates the difference: its VG 46 and VG 68 products are listed around their respective viscosity classes, while sharing many performance requirements. The number describes viscosity—not whether the additive system, base oil or approvals suit a particular machine.
What happens if oil is too thick?
- Slower cold flow
- Higher pump inlet resistance
- Increased drag and heat
- Slower actuator response in some systems
What happens if oil is too thin?
- Reduced oil-film thickness at operating temperature
- Higher internal leakage
- Possible loss of efficiency or pressure
- Less protection where the design requires a higher viscosity
Should you use VG 68 because the machine is hot?
Do not change grade to hide overheating or low pressure. Check oil level, cooler condition, filters, pump wear, relief settings and contamination. A manufacturer may permit another grade for a defined temperature range, but the service manual should make that decision.
Other properties that must match
Viscosity is only one line on the specification. Also verify hydraulic-fluid type and standards such as anti-wear performance, oxidation stability, water separation, viscosity index, zinc or zinc-free chemistry, seal compatibility and fire-resistance requirements where applicable.
Selection checklist
- Identify the machine, hydraulic system and pump.
- Find the required ISO VG grade.
- Match the required hydraulic-fluid performance standard.
- Check ambient and operating-temperature guidance.
- Confirm compatibility with the existing fill before topping up.
Browse hydraulic and industrial oils or contact MAK Group with the machine model and current fluid label.
Quick answers
Is ISO VG 68 better than 46?
No. It is more viscous, not automatically better.
Can I top up VG 46 with VG 68?
Do not mix grades unless the equipment and lubricant suppliers approve it.
Can thicker oil repair low hydraulic pressure?
No. Diagnose leakage, wear, temperature and system settings instead of masking the fault.
Technical review and sources
Reviewed by: MAK Group Lubrication Specialists. Last reviewed July 23, 2026.
الخلاصة: ISO 68 أسمك من ISO 46 لكنه مش أفضل حكماً. الاختيار حسب دليل المعدّة والمضخة وحرارة التشغيل.
