An Ultimate Guide to Hydraulic Jack Oil

Published: 03/19/22 •  8 min read

Hydraulic Jacks are used in lifting heavy objects with a small force. They are known as force multipliers.

Each hydraulic jack uses a fluid known as jack oil to transmit energy.  Hydraulic Jack oil is a non-compressible, low viscosity fluid that moves the piston and generates power in hydraulic machinery.

It can be either mineral or synthetic-based. For the smooth functioning of any jack, it is quite necessary to check the oil level and refill it at regular intervals.

For a beginner, filling jack oil is a challenging task. 

But you don’t have to worry about it. I will help you understand how you can fill a hydraulic jack with oil in five simple steps.

In addition, I will talk about the types of hydraulic fluid we generally use in a jack, jack oil viscosity grades, and finally talk about the substitutes for jack oil.

How to fill a hydraulic floor jack with oil?

Filling a hydraulic jack is an easy task but you need to do it carefully, by following these steps.

Step 1: Lose the Release Valve

First, place the jack on a hard plain surface. Then, locate the release valve and lose it. This lowers the jack so that you can access the filler plug.

The release valve can be loosened in different ways. In most jacks, you can do it by rotating the handle counterclockwise. Some jacks have a flat head, you can turn it counterclockwise. If you have any difficulty locating the release valve, you can consult your user manual.

Step 2: Remove the cover plate

Nowadays, most jacks come with a cover plate. Some screws might be holding this plate, using the appropriate screwdriver, open the plate. If there aren’t any screws, you can lift the plate up by applying force.

Step 3: Locate the filler plug and clean the area around it

Once the cover plate is removed, the filler plug must be visible to you.  Clean the area around the plug using a piece of cloth. This prevents contamination of the jack once you lift the filler plug.

Step 4: Remove the Filler Plug

Now, remove the filler plug. The plug may be a screw, you can unscrew it out using a screwdriver. In some cases, the plug pops out. Using a flat-head screwdriver, you can lift it. You have to perform this step carefully without damaging the plug. Also, clean the filler plug.

Step 5: Fill the jack with Jack oil

Now, you can check the oil level of the jack. For clear visibility, you can take a torch. If the inside is visible, then the oil level has dropped. So, you need to fill it. Pour the oil into the hole. To avoid any splashing and ensure the oil goes directly, you can use a funnel. 

Step 6: Insert back the filler Plug:

Insert the filler plug back into its place. You can either screw it back or just push it into the hole, depending on how you removed it.

Before placing any heavy load, test the lift operation of the jack.


Learn the common problems that may occur in your hydraulic floor jack.

What type of hydraulic fluid is used for the floor jack?

Now, not all types of hydraulic fluid can be used in a jack. To understand the type of oil you need to understand the purpose of this hydraulic fluid. Jack oil is used for power and heat transfer, sealing, and lubrication of the system.  The jack oil is different from other hydraulic fluids due to some characteristics discussed below:

Properties of Jack Oil:

Hydraulic Jack Oil Weight and Grade

Now, if you have seen a hydraulic oil bottle, you might have observed SAE 10 W or ISO 20 written on it. Do you know what they mean? They represent the viscosity grades of the oil.

Viscosity Grades:

The viscosity grade of an engine oil indicates how resistant it is to flowing in your vehicle’s engine. A lubricant with a low viscosity grade will be more fluid, liquid, and easy to flow. In contrast, the higher the grade, the thicker the oil, and the slower it flows, allowing a protective coating to build on engine parts.

ISO and SAE:

Now, on a jack oil bottle, two types of notations are used, for instance, ISO 22 or SAE 10W. In this example, SAE is the abbreviation of the Society of Automotive Engineers since they have developed this notation, W stands for Winter, and 10 represents the viscosity grade. On the conversion scale, the viscosity grade of 10 in SAE represents the kinematic viscosity of 22 centiStokes (cSt) at 40. The lower the number before “W”, the easier it is for fluid to work at low temperatures. A parallel grading system to SAE is the ISO system. For instance, SAE 10W is equivalent to ISO 22.

Now, there are two types of oil, based on these viscosity grades; Monograde and Multigrade. An example of Monograde oil, I have just discussed, is SAE 10W. But sometimes, you will find written SAE 10W30. This is a Multigrade oil, it provides the working at low and high conditions.  In this case, the value before “W” has the same meaning as that in Monograde oils. But the value after “W” represents the viscosity grade at high temperatures. 

For jacks, we normally use monograde hydraulic fluids of low viscosity grades. For instance, the commonly used include ISO 32 or SAE 10 W oil.

If your jack is not performing up to the mark, do read our guide to bleeding the floor jack. Bleeding the jack enhances the performance of your jack and is also considered good safety-wise as well.

Hydraulic Jack Oil Substitutes

It is usually recommended that you use the specified jack oil for your jack. But in case, you cannot find it, you can use machine oil or lightweight motor oil, and ATF.

Machine Oil or Lightweight motor oil with viscosity grades 10W, and 20W performs in the same way as the original jack oil. You can use it as a substitute.

ATF or Automatic Transmission Fluid is another alternative to jack oil but its use is limited. You can use it if you have a small hand-operated jack. ATF contains additives that can damage the seals. Automatic Transmission Fluid, unlike hydraulic fluids, is prone to foaming at high pressures. Finally, certain cylinders are made specifically for certain fluids. If that fluid isn’t utilized, the cylinder’s full potential isn’t achieved.

Some technicians suggest that you can sometimes even the baby oil or oil vegetables as a jack oil.


There are a lot of questions that people ask regarding the fluid we can use in the jack. So, let’s discuss some frequently asked questions on jack oil.

Can I use motor oil on my floor jack?

One may ask that can I use motor oil in my floor jack.  The normal high-grade motor oil cannot be used in a jack because it lacks the viscosity needed in a jack. But the lightweight motor oil of grade 10W 20W, which has desired characteristics, can be used as a substitute.

Can I use brake fluid in a hydraulic jack?

It is highly discouraged to use brake fluid in a hydraulic fluid in a floor jack. The brake fluid contains a lot of additives that are not required in a jack. Using the brake fluid will severely damage the seals of the hydraulic jack. 

Which hydraulic oil is used for trolley jacks?

Trolley jacks perform a similar function to jack oil, so the type of hydraulic oil you use is similar to the one used in floor jacks. The commonly available oils for this case are ISO 150 and 8W32.

What additives are added to the hydraulic jack oil?

Some additives are added to the jack oil to ensure its performance in diverse conditions and longevity. Some common additives include anti-rust, anti-oxidant, anti-wear, and cold flow additives.

When do I need to change the hydraulic oil?

It is a rule of thumb to replace the hydraulic oil after 1000 hours of operation. Depending on your daily usage frequency, you can calculate after how much time you need to change it. Jack oil is the working fluid of the hydraulic system, it is like the blood of the system. Without sufficient oil, the jack cannot perform lift operations. So, filling the jack with the right oil at the right time is important. Though different alternatives have been suggested to hydraulic oil, it is recommended to use the designated oil for the jack.