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Hydraulic Leaks: Common Causes and How To Address Them

Hydraulic Leaks: Common Causes and How To Address Them

Hydraulic Leaks: Common Causes and How To Address Them

Internal vs External Hydraulic Leaks

Internal hydraulic leaks occur when hydraulic fluid leaks from a high pressure area of your equipment’s hydraulic system into a low pressure area. External hydraulic leaks, on the other hand, occur when hydraulic fluid leaks out of the hydraulic system.

While both types are problematic, internal and external hydraulic leaks have different causes.

Causes of Internal Hydraulic Leaks

Internal hydraulic leaks are caused by wearing or faulty components in your heavy equipment’s hydraulic system. Common causes of internal hydraulic leaks include:


  • Worn piston seals that allow an excess of hydraulic fluid to leak around the piston
  • Worn cylinder barrels that don’t fit tightly around the piston
  • Excessive clearance between the spool and the casing in spool valves
  • Relief valves with weak springs that allow hydraulic fluid to leak back into the hydraulic fluid tank
  • Hydraulic fluid with a viscosity that is too low relative to the ambient temperature of the operating environment


Any of the above circumstances may cause or contribute to internal leakage in your machine’s hydraulic system.

For example, a piston seal that has become worn down may allow an excessive amount of hydraulic fluid to travel around the seal. The leakage of fluid from the high pressure side of the piston into the low pressure side reduces the efficiency of the hydraulic system.

Causes of External Hydraulic Leaks

External hydraulic leaks are leaks that allow hydraulic fluid to travel outside of the hydraulic circuit. These leaks are caused by degraded, pierced or faulty components that allow hydraulic fluid to leak out of the system. Common causes of external hydraulic leaks include:


  • Worn seals causing external leaks by allowing hydraulic fluid to escape from around fittings
  • Loose or damaged fittings causing hydraulic fluid to leak outside the system
  • Contaminated fluid contributing to external leaks by clogging or damaging seals and fittings
  • Overheating hydraulic fluid causing seals to deteriorate and eventually lead to leaks
  • Excessive vibration on heavy equipment can cause fittings and hose connections to come loose and leak


Generally, external hydraulic leaks are bound to occur whenever damage occurs to your machine’s hydraulic hoses, seals, cylinders and fittings.

Not only are external hydraulic leaks costly, but they can also be dangerous. It’s important to address hydraulic leaks right away and not neglect them.

What Happens if You Neglect a Hydraulic Leak?

Added Costs from Wasted Fluid

External hydraulic leaks can cause you to constantly replace your machine’s hydraulic fluid, which increases your operating costs. Even small leaks can cause a problem, as they allow contaminants to enter into the hydraulic system and contaminate your machine’s hydraulic fluid.

Damage to Other Parts of the Machine

When an external hydraulic leak occurs, contaminants are able to enter into your machine’s hydraulic system. These contaminants cause damage to other seals and fittings in the circuit, potentially leading to more leaks and part failures. 

Environmental and Safety Concerns

In the workplace, oil spills are always treated as a safety concern. Oil leaks from your machine’s hydraulic system can cause slip hazards, especially indoors.

Not only do hydraulic leaks create slipping hazards, but the leaks themselves can be deadly. Hydraulic systems contain fluid under thousands of pounds of pressure, and an external, high pressure leak has the potential to penetrate through clothing, skin and even bones.

Equipment and Operator Downtime

Like other maintenance issues, hydraulic leaks can become catastrophic – leading to significant downtime. When your machine goes down due to a hydraulic leak, it can take days or weeks to have it serviced – inflating operating costs.

Leak shown above is on a forklift hydraulic pipe system

How to Spot a Hydraulic Leak

Hydraulic leaks are generally easy to identify, although it’s sometimes difficult to pinpoint the exact location of the leak. Here are some indications your heavy equipment is suffering from a hydraulic leak:

  • Puddles of hydraulic fluid on, around or under your machine
  • Decreased hydraulic fluid levels shortly after refilling
  • Hissing or whistling sound near hydraulic components
  • Hydraulic fluid around fittings and connections
  • Decreased pressure and drifting cylinders
  • Strong unusual odors near hydraulic components


External hydraulic leaks are the easiest to identify. If your machine is suffering from an external hydraulic leak, you will notice a build up of hydraulic fluid somewhere on or around the machine.

Since external hydraulic leaks allow hydraulic fluid to exit your machine’s hydraulic system, they will also cause your hydraulic fluid levels to run low. 

If you notice you need to constantly top off your machine’s hydraulic fluid level, your machine may have an external hydraulic leak.

Internal hydraulic leaks are harder to identify. Unlike external leaks, internal hydraulic leaks will not cause a pooling of fluid on or near the machine. The most common way to spot an internal hydraulic leak is decreased performance. For example, a skid steer with a hydraulic leak in one of its cylinders may suddenly struggle to pick up and move large loads. 

You may even notice cylinder drift, which occurs when there is a leak in one of your cylinder’s pistons. If you notice your bucket slowly lowers under large loads, this could be a sign of cylinder drift.

How to Prevent Hydraulic Leaks

The best way to prevent hydraulic leaks is through a robust and consistent maintenance program. Train your operators to check their machine’s hydraulic fluid levels regularly and always replace hydraulic fluid filters on time.

Since contaminated hydraulic fluid is one of the top causes of hydraulic leaks, it’s important to keep your hydraulic fluid as clean as possible.

While topping off your hydraulic fluid is sufficient for keeping your machine operating, it does not remove the contaminants that build up in your machine’s hydraulic fluid during normal use.

Completely draining your machine’s hydraulic fluid and replacing it with new fluid is an essential part of heavy equipment maintenance. Be sure to replace your machine’s hydraulic oil according to the interval specified in its maintenance manual.

Hydraulic leaks can quickly lead to costly damages and lengthy downtime. If you need help solving your hydraulic issues, get in touch with one of our parts experts and find the OEM and aftermarket parts that’ll get your equipment back on track.

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