ISO VG 32
ISO VG 32 identifies a hydraulic oil viscosity grade. It is commonly used in portable hydraulic equipment because it flows readily through small pumps and valves.
It is still necessary to confirm the specification for the exact jack.
Red Seal 310T Technician · AMSOIL Dealer Since 2006
Jack Oil and Hydraulic Fluid
Hydraulic Jack Oil Substitute
Need oil for a floor jack or bottle jack and wondering what else you can use? The safe answer is simple: use the hydraulic jack oil specified by the manufacturer. Do not gamble with brake fluid, motor oil, gear oil or transmission fluid while a vehicle is depending on that jack.
Quick Answer
What Is the Best Hydraulic Jack Oil Substitute?
The best substitute is not another automotive fluid. It is a compatible hydraulic oil that meets the viscosity and fluid requirements listed in the jack manufacturer's manual.
Many portable floor jacks and bottle jacks use hydraulic jack oil near ISO VG 32, and some specify another viscosity such as ISO VG 46. Check the manual or manufacturer before filling it. Do not assume every jack uses the same oil.
If the correct fluid is unavailable, leave the jack out of service until the right oil can be obtained. A vehicle jack is not a good place for an improvised lubricant test.
Fluid Comparison
What Can You Put in a Hydraulic Jack?
The label on the container matters less than whether the fluid meets the jack manufacturer's actual specification. Dedicated hydraulic jack oil is the first choice.
| Fluid | Use It? | Mechanic's Answer |
|---|---|---|
| Specified hydraulic jack oil | Yes | Correct choice. Match the jack manufacturer's required viscosity and fluid type. |
| ISO VG 32 hydraulic oil | Check the manual | Common in portable hydraulic jacks, but not universal. |
| AW-32 hydraulic oil | Check compatibility | It has ISO VG 32 viscosity, but the additive package may differ. Use it only when permitted by the jack manufacturer. |
| Automatic transmission fluid | No | Many jack manufacturers specifically prohibit transmission fluid. Do not treat ATF as a universal emergency substitute. |
| Motor oil | No | The viscosity and additive system were designed for engines, not a portable hydraulic jack. |
| Brake fluid | Never | Brake fluid is chemically different and may damage seals and contaminate the jack. |
| Power steering fluid | No | Power steering fluids vary widely and are not automatically compatible with jack seals or viscosity requirements. |
| Gear oil | No | Far too heavy for most portable jack pump and valve systems. |
| Penetrating oil or WD-40 | Never | These are not pressure-bearing hydraulic fluids. |
Do Not Rely on Fluid Colour
Hydraulic fluid colour does not prove its viscosity, additive chemistry or seal compatibility. Identify the required specification, not merely a fluid that looks similar.
Understanding the Labels
Common Choice
Not Identical
Check First
ISO 32, AW-32 and Hydraulic Jack Oil
AW-32
AW-32 is normally an anti-wear hydraulic oil in the ISO VG 32 viscosity range. The “AW” describes its anti-wear additive system.
Matching viscosity does not automatically prove full compatibility with every portable jack.
ISO VG 46
Some hydraulic jack oils are ISO VG 46. That is why a blanket statement that every jack requires ISO 32 is inaccurate.
Use the viscosity specified by the jack manufacturer whenever it is available.
The Practical Answer
When the manual simply calls for a good-grade hydraulic jack oil, buy oil sold for portable hydraulic jacks. When the manual provides an ISO viscosity grade or named equivalent, match that specification.
Fluids to Avoid
Do Not Use
Do Not Use
Never Use
Do Not Use
Why Common Jack Oil Substitutes Are a Bad Bet
Automatic Transmission Fluid
ATF is itself a hydraulic fluid, but that does not make it suitable for every hydraulic system. Its friction modifiers, detergents, viscosity characteristics and seal requirements were developed for automatic transmissions.
Several jack manufacturers specifically state not to use transmission fluid. Unless the jack manufacturer expressly approves it, leave ATF out.
Motor Oil
Engine oil contains an additive package designed to manage soot, combustion acids, deposits and engine wear. A hydraulic jack has different pump clearances, valves, seals and air-release needs.
Even a light motor oil should not be treated as hydraulic jack oil.
Brake Fluid
Automotive brake fluid is not mineral hydraulic jack oil. It can be incompatible with the seals and materials used inside a jack.
Manufacturers commonly prohibit brake fluid because incorrect fluid can damage the jack and create a risk of sudden load loss.
Gear Oil or Power Steering Fluid
Gear oil is normally far too heavy. Power steering fluid varies by manufacturer and application. Neither is a dependable substitute for the specified hydraulic jack oil.
“It is hydraulic” is not enough. The viscosity, additives and seal compatibility all matter.
Damage Control
Already Put the Wrong Oil in the Jack?
Stop using it under load. Lower the jack completely, remove it from service and identify exactly what was added.
Do Not Crawl Under a Vehicle Supported Only by a Jack
A hydraulic jack is a lifting device—not a support stand. Use properly rated jack stands on a stable surface before working beneath a vehicle, even when the jack appears to be holding normally.
Small Accidental Top-Up
Drain the reservoir according to the manufacturer's procedure. Refill with the specified hydraulic jack oil and bleed the system. Do not simply dilute the wrong fluid with more oil.
Jack Was Operated or Stored
Seals may already be affected and contamination may remain in the pump and cylinder. A proper inspection, flush or rebuild may be necessary before the jack can be trusted again.
Compatibility
Can You Mix Hydraulic Jack Oils?
Avoid mixing oils unless the manufacturer or lubricant supplier confirms that the fluids are compatible. Two products may share the same ISO viscosity grade and still use different base oils or additive systems.
Mixing may affect air release, foaming resistance, seal behaviour, corrosion protection and low-temperature performance. When changing to an unknown product, the safer approach is to drain the existing oil and refill with one approved fluid.
Low Oil Does Not Always Mean the Jack Needs a Different Fluid
Hydraulic oil does not normally disappear without a reason. Inspect the reservoir plug, ram seal, pump piston and release valve area for leakage before topping it up repeatedly.
Basic Maintenance
How to Refill Hydraulic Jack Oil
Jack designs differ. Follow the owner's manual whenever its procedure conflicts with these general steps.
Lower the Jack Completely
Remove all load and fully retract the lifting ram. Place the jack upright on a firm, level surface.
Clean Around the Fill Plug
Remove dirt before opening the reservoir. Contamination can damage small pump valves and sealing surfaces.
Open the Fill Port
Remove the correct fill plug or vent screw. Do not remove an adjustment screw or overload valve.
Check the Required Oil Level
Fill only to the level specified by the manufacturer—often near the lower edge of the fill opening with the ram fully retracted. Do not assume every reservoir should be filled to overflowing.
Add the Correct Jack Oil Slowly
Use a clean container and avoid introducing air or dirt. Do not mix in an unknown leftover fluid.
Bleed Air From the System
Follow the manual's bleeding procedure. This commonly involves opening the release valve and operating the pump through several strokes before closing the valve and retesting.
Test Without Going Under a Vehicle
Check lifting, lowering and load holding from a safe position. A jack that creeps down, moves erratically or leaks requires repair.
Troubleshooting
Why a Hydraulic Jack Will Not Lift
Low oil is only one possible cause. Adding more fluid will not repair worn seals, a leaking valve or trapped air.
Release Valve Open
Confirm the release valve is fully closed using normal hand pressure. Do not overtighten it.
Air in the System
A jack may feel spongy, pump without lifting or move unevenly when air is trapped in the hydraulic circuit.
Oil Level Too Low
Low fluid may prevent full lift. Find the source of any leak before treating repeated top-ups as normal maintenance.
Reservoir Overfilled
Excess oil leaves inadequate expansion space and can cause poor operation or leakage when the ram retracts.
Dirty Pump or Check Valve
Contaminated oil can interfere with small internal valves, causing weak lifting or load creep.
Worn Internal Seals
A jack that lifts but will not hold may have internal bypass leakage even when no external oil leak is visible.
Jack Safety Is Not Optional
- Work only on a firm, level surface.
- Stay within the jack's rated capacity.
- Lift only at approved vehicle lifting points.
- Chock the wheels that remain on the ground.
- Use properly rated jack stands before working underneath.
- Never use a leaking, damaged or unreliable jack.
- Do not adjust the factory-set overload valve.
A jack that received the wrong fluid should not be trusted under load until it has been properly serviced and tested.
Frequently Asked Questions
Hydraulic Jack Oil Substitute FAQ
What is the safest hydraulic jack oil substitute?
Use a hydraulic oil that meets the specification and viscosity required by the jack manufacturer. ISO VG 32 is common, but it is not correct for every jack.
Can I use ATF in a hydraulic jack?
Do not use ATF unless the jack manufacturer expressly approves it. Many manufacturers specifically prohibit transmission fluid in their jacks.
Can I use motor oil in a floor jack?
No. Motor oil is formulated for engines and should not be used as a substitute for specified hydraulic jack oil.
Can I use brake fluid in a bottle jack?
No. Brake fluid can be incompatible with the jack's seals and internal materials. Jack manufacturers commonly warn against it.
Is AW-32 the same as hydraulic jack oil?
Not necessarily. AW-32 is an anti-wear hydraulic oil in the ISO VG 32 viscosity grade. It may be suitable when the manufacturer permits that type of fluid, but the labels are not automatically interchangeable.
Is ISO 32 correct for every hydraulic jack?
No. ISO VG 32 is common, but some jack oils and equipment manuals specify another viscosity, including ISO VG 46. Check the exact jack's requirements.
Can different hydraulic jack oils be mixed?
Avoid mixing unknown fluids. Matching viscosity alone does not prove that the base oils and additive systems are compatible.
How much oil goes in a hydraulic jack?
Capacity and fill level vary by design. Fully lower the ram and fill only to the level specified in the owner's manual. Overfilling can cause poor operation and leakage.
Why does my jack lift and then slowly lower?
Possible causes include a release valve that is not fully closed, contamination in a check valve, trapped air or worn internal seals. Do not use the jack under a vehicle until the fault is repaired.
Continue Reading
Jack Oil and Hydraulic Fluid Information
Use the Correct Hydraulic Oil
Vyscocity supplies AMSOIL hydraulic oils for shops, farms, fleets and equipment operators across the USA and Canada. Match the product to the manufacturer's required viscosity and specification before buying.