Bottle Jack Oil

Bottle jacks are remarkably powerful tools for their size, capable of lifting several tonnes with simple hand pumping. This lifting power depends entirely on hydraulic oil—the fluid that transmits force from your pumping action to the lifting ram. Proper oil selection and maintenance keeps your bottle jack working safely and reliably.

Whether you're lifting vehicles for maintenance, supporting structures during construction, or pressing bearings in a shop, your bottle jack's performance depends on what's inside it. The right hydraulic oil ensures smooth operation, protects internal components, and maintains lifting capacity across varying temperatures.

This guide covers everything you need to know about bottle jack oil—from selecting the correct type to filling procedures and troubleshooting common problems.

How bottle jack hydraulics work

Understanding the hydraulic system explains why oil selection matters so much for bottle jack performance.

Basic operation

Bottle jacks use a simple single-acting hydraulic cylinder. When you pump the handle, a small piston forces oil from the reservoir into the main cylinder. Because the main ram has a much larger diameter than the pump piston, the force is multiplied—a mechanical advantage that allows lifting heavy loads with modest effort.

A typical 20-tonne bottle jack might have a pump piston of 15 millimetres (0.6 inches) and a ram of 60 millimetres (2.4 inches). The area ratio of about 16:1 multiplies your applied force by the same factor.

Key components

Reservoir. The body of the bottle jack serves as the oil reservoir. Capacity varies from about 50 millilitres (1.7 fl oz) in small jacks to over 500 millilitres (17 fl oz) in large ones.
Pump piston and cylinder. The small-diameter pump assembly where pumping action occurs.
Main ram. The large piston that does the actual lifting.
Check valves. Ball or poppet valves that control oil flow direction.
Release valve. Controls lowering by allowing oil to return to the reservoir.
Seals and O-rings. Prevent internal and external leakage.

Every moving surface and seal in this system relies on hydraulic oil for lubrication. The oil also transfers heat, protects against corrosion, and must flow properly through small passages and valves.

Types of bottle jack oil

Several fluid types work in bottle jacks. Selecting the right one depends on your equipment specifications and operating conditions.

Hydraulic jack oil

Purpose-made hydraulic jack oil is the preferred choice for most bottle jacks. These oils are formulated with the correct viscosity for jack applications, typically ISO VG 22 or ISO VG 32. They include anti-wear additives to protect pump components, corrosion inhibitors to prevent rust, and anti-foam agents to maintain proper operation.

Jack oil is widely available at auto parts stores, hardware stores, and industrial suppliers. It's relatively inexpensive—a litre typically costs only a few euros and will service many jacks.

General hydraulic oil

Standard hydraulic oils designed for industrial equipment also work well in bottle jacks. Look for AW (anti-wear) hydraulic oil in ISO VG 22 or ISO VG 32 grades. These are essentially the same formulations sold as "jack oil" but in larger quantities and sometimes at lower per-litre cost.

Automatic transmission fluid

Some manufacturers specify automatic transmission fluid (ATF) for their bottle jacks. ATF has appropriate viscosity and contains additives that provide good lubrication and corrosion protection. If your jack's manual specifies ATF, use it—Dexron III or Mercon types are commonly recommended.

What NOT to use

Several common fluids should never be used in bottle jacks:

Motor oil. Contains detergents and additives designed for engines that can damage hydraulic seals.
Brake fluid. Chemically incompatible with most hydraulic seals—will cause rapid deterioration.
Power steering fluid. May work short-term but often has incompatible additives.
Vegetable or cooking oil. Breaks down quickly, provides poor lubrication, and attracts moisture.
Water or water-based fluids. Causes corrosion and provides inadequate lubrication.

Viscosity selection

Viscosity—the oil's thickness or resistance to flow—is the most critical property for proper jack operation.

Understanding viscosity grades

Hydraulic oils are classified by ISO viscosity grade (VG), which indicates viscosity at 40°C (104°F) measured in centistokes (cSt).

ISO Grade	Viscosity at 40°C	Best For
ISO VG 10	9-11 cSt	Very cold environments, small precision jacks
ISO VG 22	19.8-24.2 cSt	Cold to moderate temperatures, light duty
ISO VG 32	28.8-35.2 cSt	Most bottle jacks, moderate temperatures
ISO VG 46	41.4-50.6 cSt	Hot environments, heavy duty jacks

Recommended viscosity

For most bottle jacks used in typical garage or shop conditions (15-30°C / 59-86°F), ISO VG 32 provides ideal performance. This is the most commonly specified grade and what most "jack oil" products contain.

For jacks used primarily outdoors in cold weather or in unheated spaces during winter, ISO VG 22 flows better at low temperatures and prevents sluggish operation.

For jacks used in very hot environments or under sustained heavy use that generates heat, ISO VG 46 maintains better film strength and protection.

Temperature effects

Oil viscosity changes significantly with temperature. Cold oil becomes thick and resists flow, making the jack hard to pump and slow to respond. Hot oil becomes thin, which can allow internal leakage and reduce lifting capacity.

If your jack operates across a wide temperature range, consider a multi-viscosity hydraulic oil that maintains more consistent performance from cold starts to hot operating conditions.

Checking oil level

Regular oil level checks prevent many bottle jack problems. Low oil is the most common cause of poor jack performance.

When to check

Check bottle jack oil level:

Before any use after extended storage
Monthly for jacks in regular use
Immediately if the jack shows lifting problems
After any repair or disassembly

How to check

The checking procedure varies by jack design:

Fully retract the ram by opening the release valve
Place the jack on a level surface
Locate the fill plug—usually a rubber plug or screw on the side of the jack body
Remove the fill plug
Oil should be visible at or just below the fill hole level
On some jacks, a dipstick or internal tube indicates proper level

Signs of low oil

These symptoms suggest low oil level:

Ram won't extend fully despite continued pumping
Jack requires many more pump strokes than normal
Spongy or erratic pump feel
Ram extends unevenly or in jerks
Air bubbles visible when checking oil

Adding oil to a bottle jack

When oil level is low, adding the correct fluid restores proper operation. The process is straightforward but requires attention to cleanliness.

What you need

Correct hydraulic jack oil
Small funnel or squeeze bottle with narrow spout
Clean rags
Screwdriver or plug removal tool if needed

Filling procedure

Fully lower the ram by opening the release valve and pressing down if needed
Place the jack upright on a level surface
Clean the area around the fill plug to prevent contamination
Remove the fill plug
Slowly add oil using a clean funnel or squeeze bottle
Fill until oil is visible at the fill hole or reaches the specified level
Replace and secure the fill plug
Wipe off any spilled oil
Operate the jack several times to circulate oil and check for proper function

Avoiding overfill

Overfilling a bottle jack causes problems. Excess oil has nowhere to go when the ram retracts, potentially blowing seals or forcing oil out of vents. Fill only to the specified level or until oil is just visible at the fill hole with the ram fully retracted.

Bleeding air from bottle jacks

Air trapped in the hydraulic system causes spongy operation and reduced lifting capacity. Air can enter through low oil levels, during filling, or through worn seals.

Symptoms of air in the system

Soft, spongy feel when pumping
Ram bounces or settles under load
Inconsistent lifting with each pump stroke
Foamy appearance of oil when checked

Bleeding procedure

Most bottle jacks can be bled using this method:

Check and correct oil level first—air problems often start with low oil
Fully retract the ram
Remove the fill plug to vent the reservoir
Open the release valve fully
Pump the handle rapidly 10-15 times
Close the release valve
Test lift operation
Repeat if necessary until operation feels solid
Top up oil if level has dropped
Replace fill plug

Stubborn air problems

If basic bleeding doesn't resolve air problems:

Lay the jack on its side (release valve up) and pump several times to move trapped air toward the release valve
With jack on its side, crack open the release valve slightly while pumping to expel air
Return to upright, check oil level, and test

Persistent air entry after bleeding suggests a seal problem allowing air to enter the system during each pumping cycle.

Complete oil change

Periodically draining and replacing all the oil removes contamination and degraded fluid that topping up doesn't address.

When to change oil

Every 1-2 years for regularly used jacks
Annually for jacks in demanding service
Immediately if oil appears milky (water contamination) or very dark
After any known contamination event
When changing from unknown oil to correct specification

Oil change procedure

Fully extend the ram by pumping
Open the release valve to lower the ram while catching oil that flows out
Position the jack over a drain pan
Remove the fill plug
Tip or invert the jack to drain remaining oil
Allow to drain completely—several minutes for thorough drainage
Return jack to upright position
Fill with fresh oil to proper level
Replace fill plug
Bleed air using procedure above
Test operation
Dispose of old oil properly at a recycling centre

Troubleshooting oil-related problems

Jack won't lift

Possible oil-related causes:

Very low oil. Check level, add oil, bleed air.
Wrong oil type. Incompatible fluid may have damaged seals—drain and refill with correct oil, check for damage.
Severe contamination. Debris blocking valves—drain, flush, and refill.

Jack lifts slowly

Low oil level. Add oil to proper level.
Oil too thick. Wrong viscosity or cold temperature—use lighter grade or warm the jack.
Internal leakage. Worn seals allowing bypass—rebuild or replace.

Jack won't hold load

Oil too thin. Wrong grade or overheated—use correct viscosity.
Release valve problem. Debris on seat or worn valve—clean or replace.
Seal failure. Internal leakage past piston seals—rebuild required.

Oil leaking externally

Overfilled. Drain to correct level.
Worn seals. Replace affected seals.
Loose fill plug. Tighten or replace plug and gasket.
Cracked body. Usually not repairable—replace jack.

Storage considerations

Storing the jack

Proper storage preserves both the jack and its oil:

Store with ram fully retracted to keep seals lubricated
Keep upright to prevent oil from pooling in wrong areas
Store in a dry location to prevent external corrosion
Avoid extreme temperature swings that cause condensation
Check oil before use after extended storage

Storing oil

Hydraulic jack oil maintains quality for years when properly stored:

Keep containers sealed until use
Store indoors in moderate temperatures
Avoid direct sunlight
Use opened containers within a year
Keep containers clean and free of contamination

Buying guide

What to look for

When purchasing bottle jack oil:

Correct viscosity. ISO VG 32 for most applications, VG 22 for cold environments.
Hydraulic jack formulation. Specifically designed for jack applications.
Anti-wear additives. Look for AW designation.
Reputable brand. Major oil companies and tool manufacturers offer quality products.

Common products

Prestone Hydraulic Jack Oil. Widely available at auto parts stores.
STP Hydraulic Jack Oil. Another common retail option.
Mobil DTE Light. Industrial hydraulic oil, ISO VG 32.
Shell Tellus S2 M 32. Premium industrial hydraulic oil.
Generic AW 32 Hydraulic Oil. Available from industrial suppliers.

Quantity needed

A 500ml or 1-litre bottle is sufficient for multiple jacks and many oil changes. Even large bottle jacks hold less than 500ml. Buying larger quantities only makes sense for shops maintaining many jacks.

Frequently asked questions

Can I use any hydraulic oil in my bottle jack?

Use hydraulic jack oil or AW hydraulic oil in ISO VG 22 or 32 grades. Avoid motor oil, brake fluid, and other fluids not designed for hydraulic systems.

How often should I change bottle jack oil?

For typical use, every 1-2 years is adequate. Change immediately if oil looks contaminated, milky, or very dark.

Why is my bottle jack spongy?

Air trapped in the hydraulic system causes spongy operation. Check oil level first (low oil allows air entry), then bleed the system using the procedure described above.

Can I mix different brands of jack oil?

Yes, if they're the same type (petroleum-based hydraulic oil) and similar viscosity grade. Don't mix different oil types or significantly different viscosities.

Is ATF okay to use in bottle jacks?

Only if the manufacturer specifically recommends it. Some jacks are designed for ATF; others are not. Check your manual.