How to Refill & Bleed a Hydraulic Jack

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A guide to refilling and bleeding hydraulic floor, bottle, or car jacks
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A hydraulic jack is a device used to lift heavy objects, usually cars or trucks. The system works by using oil to grease the internal mechanism. If you’ve just bought a new jack, it won’t have any oil in it and you’ll have to fill it. Jacks also require oil refills every few years. First, remove the cover plate and filler plug. Then fill the chamber with hydraulic jack oil. Finally, follow the procedure to bleed excess air in the system, and your jack should be in good working order.

How do you refill a hydraulic jack?

With the jack on level ground, open the release valve and remove the cover plate and filler port plug. Slowly add hydraulic jack oil to the reservoir until it’s full. Replace the cap, then pump the jack handle 10–15 times to bleed the air. Close the release valve and test the jack to make sure it’s working.

Section 1 of 5:

Filling a Hydraulic Jack with Oil

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  1. This prevents the jack from rolling while you work on it. It also makes it easier to see when the chamber has enough oil in it. [1]
    • Also, put down a drop cloth or towels that you don’t mind getting dirty, just in case you spill some oil.
  2. This lowers the jack so you can access the filler plug. Different jacks may have different release mechanisms. On some jacks, turning the handle counterclockwise lowers the press. If you’re unsure how your jack releases, consult your owner’s manual. [2]
    • Keep the release valve open while you work.
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  3. Depending on your jack model, there may be a cover plate that protects the jack’s internal mechanism. Remove any screws holding this cover in place. Then lift the cover off. [3]
    • Depending on the type of jack you have, the cover plate might come off entirely or just lift up. If the plate comes off, keep it in a safe place so you don’t lose it.
    • Usually these screws require a Phillips head screwdriver, but check your particular model to see what type of screwdriver you need.
    • Don’t lose the screws you remove. Keep them in a safe place so you can put the cover back on later.
  4. The filler port is where you will pour the oil. To prevent dirt or grime from contaminating the jack oil, use a rag and clean off the area around the filler plug.
    • If you’re filling a new hydraulic jack, you don’t have to do this.
    • If your jack is old and there is a lot of caked on dirt around the fill plug, try spraying a hose or pressure washer to remove the gunk first.
  5. This plug is underneath the cover plate on most jacks. Depending on your jack model, the plug might unscrew or just pop out. If it is a screw type, use a screwdriver and turn counterclockwise to remove the plug. If it pops out, insert a flathead screwdriver or another flat tool under the plug and lift it out. [4]
    • If you have a bottle jack, the filler port will probably be on the side of the jack. Leave the jack upright to fill the reservoir. [5]
    • If you can’t locate the filler port, check the owner’s manual for your jack.
    • Be careful not to damage the plug when you remove it. If it doesn’t come out easily, stop and reassess what you’re doing. Don’t force it out.
  6. If you see a lot of debris in the oil or it looks black or especially thick, tip the jack to carefully pour out all of the old oil into a sealable container, like a metal coffee can. Once the jack is empty, turn it back over, then wipe the area around the filler port to ensure it’s clean. [6]
    • Dispose of this oil in accordance with the hazardous waste disposal laws where you live.
  7. Slowly pour until the oil is just below the lower rim of the fill hole. Wipe away any excess oil on the rim. [7]
    • Some brands of hydraulic jack oil have a narrow spout top that makes it easy to precisely pour the oil into the filler port. If your bottle doesn’t have a spout, use a funnel instead.
    • Do not use any motor oil, brake fluid, or any other type of oil besides hydraulic jack oil.
  8. Either push the plug back into the hole or screw it back in by turning it clockwise. [8] After the plug is in place, follow the procedure to bleed air out of the hydraulic system .
    • Do not replace the cover plate yet. You still need to bleed the air from the mechanism before moving on, and the cover plate will get in the way.
    • Some people prefer to leave the plug out while they bleed the air in case they need to add more oil. Also, depending on the jack model, you may need to keep the fill plug out while you bleed the air. Consult your owner’s manual for the correct process. [9]
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Section 2 of 5:

Bleeding the Air

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  1. You should always bleed the air after filling the jack, so the release valve should still be open. But if it isn’t, open the release mechanism all the way completely to lower the jack. Leave the release valve open while bleeding the air. [10]
    • The bleeding process is important because air can build up in the hydraulic system while you change the oil. If air is in the system, the jack won't rise properly and could even collapse. Bleeding the jack removes the air and makes the jack function correctly.
    • If you notice that the jack feels spongy or isn't lifting evenly, it could be due to air in the reservoir—follow the steps for bleeding the air out of the jack, and add more oil if needed.
  2. This pushes air out of the jack system. With the release valve open, the jack shouldn’t rise while you pump. If it starts rising, double check to make sure the release valve is open. [11]
    • Some jack models have different variations on how to bleed the air. Check with your owner’s manual to see if your model uses a different method.
    • It’s a good idea to check the oil in your reservoir after you bleed the air. If the level drops, add a little more oil.
  3. Turn the handle clockwise to close the release valve, then pump the jack to make sure it’s working. It should rise in smooth, even motions. Pump it all the way to the top and then release it. [12]
    • If the jack is jerky or doesn’t rise to the top, there is probably still air in the system. Repeat the bleeding procedure in this case. [13]
  4. With the process done, you can now reinstall all the pieces you removed. Put the cover plate back in place and screw it in with the screws you removed before.
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Section 3 of 5:

Signs the Jack Needs Oil

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  1. As the oil level decreases, air will build up inside the jack. This will cause the jack to feel spongy when you move the handle, or the jack might not lift all the way. It may also fail to lift at its full capacity. [14] Other signs that the jack needs oil might be:
    • The jack lifts slowly or unevenly, feels unstable, or sways
    • It’s leaking oil or you see oil stains under the jack
    • You see air bubbles in the reservoir
    • The jack rattles or makes other noises when you use it
    • Change the oil every 3 years, or more if it looks dirty.
Section 4 of 5:

Choosing Hydraulic Jack Oil

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  1. It’s important to use the right kind of oil in a hydraulic jack—only use hydraulic jack oil . The wrong oil could be corrosive or could otherwise damage the jack—which could lead to injury or even death if the jack fails when it’s under load. [15]
    • Do not use brake fluid or motor oil in a hydraulic jack.
    • Do not mix different types of oils in the jack.
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Section 5 of 5:

Maintaining Your Hydraulic Jack

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  1. Before you use the jack (every time), thoroughly check the jack for cracks, corrosion, or broken parts. Pump the jack up to its full extension to make sure it’s working properly. If it’s damaged or isn’t working correctly, do not use the jack. [16]
    • If any of the seals are leaking oil, replace the seals before you use the jack.
    • Check the oil before every use—if it’s low, refill it, and change it if it looks dirty. Also, replace the oil if it’s been more than 3 years since the last change. [17]
  2. Wipe any oil off of the jack before you put away—oil will attract dust, which can then get into the reservoir and contaminate the hydraulic oil.
    • When you store the jack, retract the pump and piston completely to reduce the chance that they’ll be damaged. [18]
    • Store the jack in a dry location out of the reach of children. [19]
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  • Question
    What can I use as a hydraulic oil substitute in a jack?
    wikiHow Staff Editor
    Staff Answer
    This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.
    wikiHow Staff Editor
    Staff Answer
    If you don’t have access to hydraulic jack oil, you can use machine oil or 10/20W lightweight motor oil in a pinch. Automatic transmission fluid will also work if you don’t have any other options. However, it’s not recommended that you use substances that aren’t designed for use in a hydraulic jack, since using the wrong kind of oil can damage the seals in your jack.
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  • Question
    What is the difference between hydraulic fluid and hydraulic oil?
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    Staff Answer
    This answer was written by one of our trained team of researchers who validated it for accuracy and comprehensiveness.
    wikiHow Staff Editor
    Staff Answer
    Hydraulic oil is a type of hydraulic fluid, but not all hydraulic fluids are oils. Other types of hydraulic fluids include water, glycols, and sodium-potassium alloys. Hydraulic oil serves as both a lubricant and a power-transfer medium in hydraulic machinery.
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    Is hydraulic oil a hydrocarbon?
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    Staff Answer
    Hydraulic oil is often mineral oil based, so it typically contains hydrocarbons. Hydrocarbons can be very dangerous if they enter the lungs, e.g. if someone swallows some of the fluid and accidentally inhales some of it. Always keep hydraulic oil away from children.
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      • Always check your owner’s manual before carrying out maintenance on your jack. Different models have different mechanisms.
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      References

      1. ↑ https://manuals.harborfreight.com/manuals/56000-56999/56736-792363567589.pdf
      2. ↑ https://manuals.harborfreight.com/manuals/56000-56999/56736-792363567589.pdf
      3. ↑ https://youtu.be/B2LtkQgj1gI?t=86
      4. ↑ https://youtu.be/B2LtkQgj1gI?t=105
      5. ↑ https://youtu.be/KJGl9z-Aw4c?t=2
      6. ↑ https://manuals.harborfreight.com/manuals/56000-56999/56736-792363567589.pdf
      7. ↑ https://youtu.be/B2LtkQgj1gI?t=134
      8. ↑ https://youtu.be/B2LtkQgj1gI?t=172
      9. ↑ https://youtu.be/KJGl9z-Aw4c?t=128
      1. ↑ https://media.hcrcnow.com/uploads/drawings/searscraftsman50139floorjack3ton.pdf
      2. ↑ https://media.hcrcnow.com/uploads/drawings/searscraftsman50139floorjack3ton.pdf
      3. ↑ https://youtu.be/xSAhXT0bVls?t=98
      4. ↑ https://media.hcrcnow.com/uploads/drawings/searscraftsman50139floorjack3ton.pdf
      5. ↑ https://manuals.harborfreight.com/manuals/56000-56999/56736-792363567589.pdf
      6. ↑ https://media.hcrcnow.com/uploads/drawings/montgomery_ward_6185044.pdf
      7. ↑ https://manuals.harborfreight.com/manuals/56000-56999/56736-792363567589.pdf
      8. ↑ https://manuals.harborfreight.com/manuals/56000-56999/56736-792363567589.pdf
      9. ↑ https://media.hcrcnow.com/uploads/drawings/montgomery_ward_6185044.pdf
      10. ↑ https://manuals.harborfreight.com/manuals/56000-56999/56736-792363567589.pdf

      About This Article

      Article Summary X

      To add oil to a hydraulic floor jack, start by making sure the jack is completely lowered by turning the jack’s release valve counterclockwise until it’s as low as it can get. Once the jack is lowered, locate the oil filler port, which is on the bottom of the jack’s reservoir near the flat base. Then, remove the plug or screw from the oil filler port, insert the oil can nozzle, and pour the oil in until it starts to leak out of the port. Finally, replace the filler port nozzle to use your hydraulic jack. For more advice, like how to add oil to a hydraulic bottle jack, read on!

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        Apr 20, 2021

        "Great presentation - info on bleeding the air allowed me to restore jack to full lift - when I needed it! Yay! for ..." more
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