ISO 32, 46 or 68? Which Hydraulic Oil Does My Machine Need?

Your hydraulics are sluggish on cold mornings, the log splitter manual names a grade you don't recognise, or you wonder whether a cheaper ISO 46 matches the dealer's oil.

The short answer: match the grade, type and specification in your manual. PartsForMachines lists around 130 oils and fluids from Castrol, Shell, Q8, Fuchs, HyperDrive and Draper in its Hydraulic Oil range, from 1-litre bottles to 1,000-litre IBCs.

ISO 32, 46 or 68: Which Grade Should I Use?

Use the grade in your machine's manual, and its temperature table if it offers a choice. The number tracks the oil's viscosity at 40°C, so an ISO 46 oil measures about 46 mm²/s. ISO 32 is the lighter grade for mobile machines and cooler conditions, 46 is the most common general-service grade, and 68 is heavier, for warm weather and higher-pressure work.

Viscosity swings with temperature: the Tellus S2 MX 46 measures 580 mm²/s at 0°C, over twelve times its 40°C figure. Oil too thick for the cold makes everything sluggish, while oil too thin for the heat slips past pump and valve internals, so functions slow as it warms.

Is a Cheaper ISO 46 Oil as Good as the Dealer's?

It can be, if its label lists the type and standard your manual asks for. ISO 46 fixes only the viscosity; the additives decide the rest. A mini digger that calls for HLP 46 needs an oil listed to DIN 51524 Part 2, the anti-wear class, which lines up with HM under ISO 11158. A rust-and-oxidation (R&O) oil of the same grade lacks that anti-wear package.

Where the manual names a pump maker rating, match that too: the Shell Tellus S2 MX 46 hydraulic oil, for example, is designed to meet Parker Denison HF-0 and Bosch Rexroth RDE 90245.

Can I Use Tractor Fluid (UTTO) Instead of Hydraulic Oil?

Only where the machine's maker specifies it. A universal tractor transmission oil (UTTO) is made for tractors whose transmission, hydraulics and oil-immersed brakes share one oil. It is approved against tractor specifications rather than hydraulic ones: the Spirax S4 TXM UTTO lists John Deere JDM J20C, Massey Ferguson M1143 and ZF TE-ML 03E, for example.

If your manual names a tractor fluid specification, choose a UTTO that lists it. If it names an ISO grade with HM or HV, use hydraulic oil. And if tractor fluid has gone into a digger by mistake, ask the dealer before working it.

Does Hydraulic Oil Need Changing if It Still Looks Clean?

Yes, at the interval the equipment maker sets, even if the machine runs well. Looks are a poor guide, because oil ages chemically and only used-oil analysis shows how far. The same test shows whether the interval suits your machine's work.

Act sooner if the oil turns milky, usually a sign of water, or darkens noticeably, which can mean it is oxidising. A lab sample can confirm either.

What Should I Check Before I Buy Hydraulic Oil?

• The ISO grade in the manual, and its temperature table if it gives one.
• The type: HM or HLP for general service, HV or HVLP where temperatures swing widely.
• Any standard or pump maker rating named, such as DIN 51524 Part 2 or Denison HF-0, and whether zinc-free oil is required.
• Whether the manual calls for a tractor fluid (UTTO) specification instead.
• Pack size: a 1-litre bottle for top-ups, 20 litres, a drum of about 200 litres or a 1,000-litre IBC.

Manual missing or unclear? Contact the PartsForMachines team by WhatsApp, telephone or email with the machine make and model, or browse the Hydraulic Oil range.

Pack sizes, delivery options and returns terms are shown on each product page. A 30-day return policy applies to eligible items.

Frequently Asked Questions

What oil should go in a log splitter?

Whatever grade and type its manual names: an oil listed to that ISO grade and HM or HLP class matches it on paper. No spec given? Ask the maker or our team. If it takes HLP 46, the Millmax 46 1-litre hydraulic oil suits top-ups.

Why are my hydraulics slow on a cold morning?

Cold oil is far thicker, so everything feels sluggish until it warms up. Let the engine run until the oil is warm before heavy work. If it happens every winter, check whether your manual allows a lighter grade or an HV oil.

What does an HV hydraulic oil do?

It holds its viscosity more evenly as temperatures change, thanks to a higher viscosity index (VI). The Tellus S2 VX 46 HV oil has a VI of 143, against 105 for the HM MX 46, so it suits machines working across a wide temperature range.

Are hydraulic oils zinc-based or zinc-free?

Both exist, and both can give anti-wear protection. Hyspin AWS, Haydn and HyperDrive HM oils are zinc-based, while Hyspin HVI and Tellus S3 M are zinc-free, also called ashless. Follow the equipment maker's specification if it names one.

What is the difference between UTTO and STOU?

A UTTO lubricates a tractor's transmission, hydraulics and wet brakes, but not the engine; a STOU covers the engine too. On a shared sump, whatever goes into the transmission also feeds the hydraulics, so use only a fluid that lists the tractor's specification.

Why does my ram jerk, or the pump whine?

Suspect air in the oil, which can make rams jerk and the oil foam. Check the oil level, then look for leaks on the pump's suction side. Low oil, or oil too thick for the cold, can also make a pump noisy.

Is it normal for hydraulic oil to run hot?

Warm is normal, hot is not: above about 60°C, oil life roughly halves for every further 8 to 10°C, and seals harden. Keep the cooler and tank clean, and return levers to neutral promptly, since oil forced over the relief valve becomes heat.

Why does my hydraulic oil keep going milky?

Water is usually still getting in: look for condensation in the tank, a faulty breather or worn seals, and washing-down water. Fix the entry point, then change the oil, because water speeds its breakdown and can damage internal parts.

Does hydraulic oil have a shelf life?

Yes. Store it sealed in the original container, in a clean, dry place away from temperature extremes. Keep an IBC in a covered, bunded area with its tap and breather clean, so moisture and dirt stay out.

Can I buy hydraulic oil in bulk for several machines?

Yes: 20-litre packs, drums of 199 to 209 litres and 1,000-litre IBCs such as the Hyspin HLP-Z 46 IBC. One oil only serves several machines if every manual lists that grade and type, so check the digger, telehandler and tractor separately.