Informational Guide

How To Fill a Floor Jack With Hydraulic Oil

If you own a floor jack, maintenance is critical to keep it working safely. In addition, you must know how to fill a floor jack with hydraulic oil, and it doesn't take a lot of expertise to figure out. In this guide, we cover how to add hydraulic fluid to a floor jack. 

How do you fill a hydraulic floor jack? Start by gathering all of your supplies before you get started, so you aren’t hunting for gear after you begin. You also want to read the owner’s manual because different brands have varying steps. 

Supplies Needed 

  • Hydraulic fluid 
  • Flathead screwdriver 
  • Clean rags 
  • Flashlight 
  • Funnel 

It doesn't matter if you have a smaller 2-ton jack or are using a heavy-duty 4-ton jack; the instructions are mostly the same. The only difference is the amount of hydraulic oil you might need.  

Place your jack on a level surface so it doesn’t roll away. It should also be a hard surface, so the jack can’t sink. Loosen up the release valve. Some are turned with a flathead screwdriver, while others require you to turn a unique handle. Once the oil flows back into the main reservoir, your floor jack will completely lower.  

With some jacks, you might need to remove the cover plates. Open up the oil plug, usually found at the bottom of the reservoir, although it can also be at the top. With a clean rag, wipe up any oil seepage that’s occurred around the plug.  

Examine how much oil is in the system. With a flashlight, you should be able to see the amount of oil inside. With a funnel, pour some hydraulic fluid into the jack. The amount of oil you need depends on how low the reservoir is. Make sure you have more than enough hydraulic fluid on hand before you get started. Once the system is full, you are ready to close up the reservoir.  

Screw back on the filler plug. Clean the area once again with your rag. If you had to take the cover plates off to fill the system, it’s also time to put them back on. Once you fill the jack, you want to keep a close eye on it to ensure there are no leaks. 

Fill A Floor Jack With Hydraulic Oil

What Kind Of Oil Do You Put In Floor Jacks? (Hydraulic Vs. Alternatives) 

Before you learn how to fill a hydraulic floor jack with oil, you should know the appropriate type to use. Hydraulic oil is a non-compressible, low viscosity fluid that helps move the piston and power the machinery. In general, hydraulic fluids can be either synthetic or mineral-based. 

Some of the best choices for your floor jack are: 

  • ISO 150 
  • AW32  

The viscosity of hydraulic fluid gets measured by Centistokes (cSt). It can be measured as 1000C (SAE) or 400C (ISO). Additives can also be put in hydraulic fluid for different purposes. Some allow the floor jack to perform better in differing conditions. You can choose anti-rush, anti-wear, anti-oxidant, and cold flow options.  

There are some fluids that should never be used as you learn how to refill hydraulic oil in a floor jack. Stay away from motor oil or brake oil, as these don't have the proper viscosity and could break the seals. In some cases, you might be able to use some automatic transmission fluid, but the viscosity must match. Additionally, if the ATF has additives, the seals of your jack could be damaged.  

When Should You Add Oil To A Floor Jack? (Maintenance Guide) 

As part of your floor jack maintenance, you want to ensure that the oil is always topped off. Hydraulic fluid should continue working for approximately three years when the jack is cared for. However, you should check the system often and fill it up as needed to ensure proper operation. 

If you notice any trouble using the floor jack, it’s best to change the hydraulic fluid to see if that makes a difference. If not, you might need to get the floor jack looked at by a professional. Whatever you do, don’t use a floor jack that isn’t holding a load properly, or you could end up hurt.  

When To Add Oil To A Floor Jack

Common Floor Jack Hydraulic Oil Questions 

How do you fix a floor jack that won’t lift?  

In many cases, you simply need to learn how to put oil in a hydraulic floor jack because the system is low. Start by looking in the reservoir to see if some oil will fix the problem. Otherwise, you might need to fix something mechanically.  

Can you use vegetable oil for hydraulic fluid? 

In a pinch, you can use vegetable oil, but it’s not meant to last as long as hydraulic fluid. For this reason, it’s best to learn how to refill a floor jack with hydraulic fluid. 


Now you know how to put hydraulic fluid in a floor jack, allowing you to keep your equipment in perfect running condition. With a reliable jack in your garage, you can get your jobs done much faster and efficiently.