ISO 32 vs 46 hydraulic oil
Updated: 23 October 2026
Two cans look the same until you read 32 on one and 46 on the other, and it is tempting to treat the higher number as the better oil or to mix them. ISO 32 vs 46 hydraulic oil is viscosity at 40 °C, and the manual already picked a side. These notes use public UK explanations of ISO VG and the amazon.co.uk listings captured on 21 October 2026. This is not a lab test of Silverhook or HMT. A qualifying purchase can earn us a commission at no extra cost to you. The bottle table is the [hydraulic oil comparison](/hub/diy-supplies/hydraulic-oil).
Two cans look the same until you read 32 on one and 46 on the other, and it is tempting to treat the higher number as the better oil or to mix them.
Two cans look the same until you read 32 on one and 46 on the other, and it is tempting to treat the higher number as the better oil or to mix them. ISO 32 vs 46 hydraulic oil is viscosity at 40 °C, and the manual already picked a side. These notes use public UK explanations of ISO VG and the amazon.co.uk listings captured on 21 October 2026. This is not a lab test of Silverhook or HMT. A qualifying purchase can earn us a commission at no extra cost to you. The bottle table is the hydraulic oil comparison.
Our top picks
| Badge | Product | Grade on the label | Pack size | Stated use | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  HMT HMT ISO VG 68 hydraulic oil, 20 litres | ISO VG 68 (title). Viscosity field says 1. | 20 litres | Industrial hydraulics, plant, jacks, agricultural machinery and mobile equipment, on the bullets | 5.8 | about £78.83 | View offer |
| Alternative |  Silverhook Silverhook ISO 32 hydraulic oil, 5 litres | ISO 32 (title and viscosity field) | 5 litres | Construction and manufacturing on the attribute line. Reviews cite jacks, splitters and compressors. | 7.8 | about £23.98 | View offer |
| Best value |  HMT HMT ISO VG 46 hydraulic oil, 20 litres | ISO VG 46 (title and viscosity field) | 20 litres | Industrial hydraulic power, and mobile plant such as excavators and cranes, on the bullets | 7.8 | about £65.49 | View offer |
On this page
The number is viscosity, not quality
ISO VG is kinematic viscosity at 40 °C. ISO 3448 places each grade in a band of about plus or minus 10 percent. ISO 32 sits near 32 cSt, ISO VG 46 near 46, and ISO VG 68 near 68. Pirtek says most applications it sees are 32 or 46. The number is not a higher additive pack.
ISO VG 68 is a thicker oil at the same test temperature, not a premium ISO 32. Hot and heavily loaded, the thinner oil can lose film. If you still need the family of bottle, start on choose the family first.
When 32, when 46, when 68
Use ISO 32 when the plate says 32, often the colder or lighter mobile job. MA Hydraulics describes 32 for colder running, 46 as the usual moderate-temperature start, and 68 for warmer or heavier duty. A merchant’s 10 °C step is a rule of thumb, and it does not overrule a plate.
Use ISO VG 46 when the plate says 46. In this set that is HMT’s 20 litre pail, HMTH00820L, at about £65.49, about £3.27 a litre, with 4.7 from 267 reviews, and only then is it best value per litre. A jack that asks for jack oil is not that situation. Use ISO VG 68 when the plate says 68. HMT’s other pail is about £78.83 with no review text. The cans that print 32 or 46 are on which can is 32 or 46.
Do not mix them
Mixing ISO 32 and ISO VG 46 feels like a compromise and behaves like an unknown oil. Bosch Rexroth does not generally allow mixing, including fluids that share a classification, and it treats more than about 2 percent of another fluid as a mixture. Two oils can both say 46 and still differ in additives.
A mystery fill is not restored by adding a careful 46. Drain and refill with the grade the current sheet names, and take the old oil to a recycling centre. GOV.UK treats hydraulic oil as hazardous waste. A top-up of the same named product is different. Another can of Silverhook ISO 32, when the plate agrees, is a top-up. Crossing to HMT 46 to finish a cheaper can is the 2 percent problem as soon as the pour is more than a trace.
What this set actually prints
The only ISO bottles in this set are Silverhook ISO 32, in 1 litre and 5 litres, and the two HMT pails, ISO VG 46 and ISO VG 68, both sold as 20 litres. Jack oils print 10W, not an ISO VG. Comma CHF 11S is about 19 cSt at 40 °C on Comma’s own page, a different family from these grades.
Silverhook’s 1 litre title says ISO 32, at about £10.45. A bullet says SAE 10W and the SAE J300 cell says 20W-40. SAE 10W is not a synonym for ISO 32. The 5 litre can, model SHRH5, shows a unit count of 4,540 ml and part number SHRH4. None of that changes 32 into 46. HMT 46’s title is the grade. The 35 fl oz field cannot describe an 18 kg pail, and HMT 68’s viscosity attribute says 1. Ignore both cells.
Common questions
Is 46 better than 32?
No. ISO VG 46 is thicker at 40 °C than ISO 32. Better means the grade your pump and your climate were specified around. A higher number can be worse on a cold start and right in a hot, heavy circuit. Pirtek’s general note that most jobs are 32 or 46 is not a reason to upgrade a plate that says 32.
When is 68 the right grade?
When the machine documentation says ISO VG 68, often for warmer running or heavier duty in the cross-reference tables UK hydraulic firms publish. In this set the matching pail is HMT’s 20 litres at about £78.83. A 5.0 from three ratings, with no review text and a viscosity field that says 1, is not a reason to prefer it over a specified 46.
Can I mix 32 and 46 to split the difference?
No. Bosch Rexroth does not generally allow mixing, including oils of the same classification, and treats more than about 2 percent of another fluid as a mixture. If the oil in the tank is a mystery, drain and refill with the grade on the sheet.
Does SAE 10W mean ISO 32?
Not on these listings. Silverhook prints ISO 32 and also mentions SAE 10W, and the 1 litre SAE cell says 20W-40. Jack oils print 10W and do not print an ISO VG. Follow the ISO line on an ISO oil, and the jack sheet on jack oil.
Are HM and HLP the same stamp?
They are related words for anti-wear hydraulic oil, HM in ISO 11158 and HLP in DIN 51524-2, and the test lists are not the same document. Seeing both on an HMT 68 bullet is a claim on that listing, not proof this comparison has checked the pail against either standard. The VG number is still the thickness you match first.
Related pages
Sources
Public UK sources and the amazon.co.uk listings compared on this page. Prices and stars are the 21 October 2026 capture. Updated 22 October 2026.
- GOV.UK: vehicle and oily wastes (retrieved 22.10.2026)
- HSE: hydraulic injection injury (retrieved 22.10.2026)
- MA Hydraulics: hydraulic oil cross reference (retrieved 22.10.2026)
- Sealey 2100TB instructions (retrieved 22.10.2026)
- Comma: MVCHF central hydraulic fluid (retrieved 22.10.2026)
- Fuchs UK: TITAN CHF 11S (retrieved 22.10.2026)
- Oil Care: waste oil (retrieved 22.10.2026)
- Bosch Rexroth: mixing limit (retrieved 22.10.2026)