How To Repair a Floor Jack That Won’t Hold Pressure

By Jed Lehman •  Updated: 11/23/21 •  7 min read

If there’s one tool that’s impossible to substitute in your garage or workshop, it’s the hydraulic jack. Nothing else can do what a jack does safely or effectively. So setting up, only to watch your jack slowly deflate like a stuck balloon can make you feel sick to your stomach.  

Luckily, diagnosing the problem is normally pretty simple. Most common issues can be fixed in five minutes at home with things you already have, or with a quick trip to the hardware store. 

Why Isn’t My Hydraulic Jack Working?

Honestly, figuring out if your jack isn’t working is pretty simple. It’s the why that’s hard. 

Hydraulics Issues

The hydraulic system is the heart of your jack and the mechanism that does all the hard work, by using a pressurized cylinder of hydraulic oil to lift the weight on top of it. 

Hydraulic jacks operate on a closed system. While this requires very little maintenance, issues can spring up from time to time. Too much or not enough hydraulic fluid will stop the cylinder from pressurizing and the jack from lifting and weight, and a loose seal can let air into the system and cause further problems. 

Thankfully, the fix is easy. Make sure that the oil is at the right level, and that the release valves are sealed before use. 

Trapped Air

Like any hydraulic system, it’s possible for air to slowly leak into the cylinder of your jack over time. To fix this problem, you need to bleed the hydraulics, which is a relatively quick and simple job. 

Start by opening the release valve. Pump the handle a few times, then slowly open the oil filler plug. This can be found on the hydraulic cylinder itself, and it’s normally a small rubber grommet.

The easiest way to open the filler plug is a thin, flat tool, like a flat head screwdriver. Open the oil filler slowly, and just enough for the trapped air to free itself. Be careful when you open the oil plug, as you’ve just pressurized the chamber, so oil could spray from the plug if it’s opened too quickly.

Now is also a good time to check if your jack needs an oil top-up or replacement. Once complete, replace the plug and check that the jack is working correctly. Sometimes you’ll need to repeat this process a couple of times to completely clear any trapped air.  

The Overload Valve has Been Triggered

A hydraulic jack’s overload valve will trip when too much weight has been put on the jack, exceeding its safety limit. It’s a safety feature that stops you from overloading your jack and putting yourself at risk. 

An overload valve is something that shouldn’t be fixed at home. If it triggers, take your jack to a hydraulics expert, as trying to repair it without specialist tools can damage the internal hydraulic spring and permanently ruin your jack. 

What to do When Your Hydraulic Jack is Leaking

A jack that’s leaking is never a good sign. Luckily, it’s normally a simple fix. Two common issues can cause a jack to leak. To check what’s wrong, start by taking a look at the liquid that’s leaking out of your jack. 

Your Jack is Leaking Hydraulic Oil

An oil leak is normally caused by old or worn o-rings causing a bad seal. These should always be replaced first if you can’t find any other reason for leakage.   

The Oil Leak is Milky or Bubbling

If the fluid leaking out of your jack is full of bubbles or has a milky, streaky consistency, this is a sign that there’s a lot of air getting into the hydraulic chamber. 

To fix this, change the hydraulic oil and regularly clean the jack’s drain plug. A quick wipe with a rag when you’re finished is generally enough.  

What to do if the Frame of Your Jack is Damaged

The worst has been left to last. If the frame of your jack is cracked or bent, it should under no circumstances be used to lift anything heavier than your morning cup of coffee. 

The frame of a jack is designed specifically to support the rated weight and damage will compromise the structural integrity, meaning there’s no telling if or how badly it will fail, and it’s guaranteed a tool always fails at the worst possible time.  

If the frame of your jack is damaged, the only possible fix is to buy an entirely new one.  

How to Look After Your Hydraulic Jack to Prevent Long Term Damage

Like any tool, time and wear can slowly cause your jack to fail over time, but smart choices and looking after it correctly will lead to a much longer effective lifespan. Here’s what you need to know. 

Safe Weight Limits and Overloading

Every jack comes with a weight limit that will have been extensively tested by the manufacturers. Most jacks will also have a safety documentation sticker that details how much weight a jack can lift. This is normally placed on the hydraulic cylinder.  

Weight limits vary, depending on the type and style of jack, and can also change based on how a jack is being used, and how high you’re suspending the vehicle on top of it. This is a topic too broad in scope for this article, but as a general rule, never exceed the stated safe working weight of a hydraulic jack. This can cause the jack to catastrophically fail, which puts you and anyone else around you at risk of serious harm. 

What Type of Fluid Should be Used for a Hydraulic Jack?

The answer, unsurprisingly, is hydraulic jack oil, which should be available at any good auto parts store, garage, or hardware store. 

You can use lightweight motor oil or machine oil if you’re in a bind and urgently need to top up your jack. Long-term use can potentially damage the hydraulic mechanism, so it shouldn’t be turned to as your first choice. 


The metal frame and working parts of a jack are susceptible to rust and corrosion. Mechanical wear or pressure can cause the mechanism to seize or stall, especially on an older jack that has been left in rough conditions. 

The fix is simple. Lubricate well and often. WD40 is your friend, and regular maintenance will slow the wear that comes with age and use.   

General Maintenance

Questions? Contact us here.

Jed Lehman

Jed Lehman is a born gearhead who has been working on cars since he could crawl. He inherited his love for auto from his grandfather who owned a maintenance shop in Carlsbad, California. Jed is the driver behind Gearshift, and started this site to provide straightforward, helpful automobile information. From maintenance tips to product reviews, you can find it all here.