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Why is my Machine Leaking Hydraulic Fluid? 8 Common Reasons You Experience an Internal or External Leak

When it comes to hydraulic leaks it rarely rains, it pours. And even when a leak may seem minor, it can lead to excessive maintenance and operational costs, poor performance, a lack of reliability and accelerated component wear.

Tracking down the source of a leak, including whether it is internal or external, can be difficult. However, addressing the issues causing that leak will save unnecessary expenses later on.

External Leaks:

Visual inspection is the initial means for tracking down the source of an external leak. This requires external cleaning of the equipment so that the fluid can be spotted at its origin. 

Some leaks can have obvious origins, such as a hydraulic line that has begun to spray fluid at high pressure from a small tear or hole in the line. Others, however, can be tricky because leaks can easily drip and run from place to place if their source is high on the machine. Therefore, the place where the fluid gathers (for example a puddle on the floor or on the machine itself) is not necessarily in the same place that the hydraulic fluid is actually exiting the system. The use of a dye-additive to the fluid, specifically one that will not compromise its performance but allows leaks to show up under a black light, will often enhance visual inspection for external leaks.

Most external leaks are the result of:

  • Failed seals. In many cases the seals may have exceeded their limited useful life.
  • Loose or broken connections.
  • Hydraulic hoses. If holes or cuts are found in hoses, then additional effort needs to be made to prevent the same damage from occurring to a new line, for example through use of a protective covering, rerouting the line, etc.
  • Leaking pipes.


Tracking down external leaks is usually easier than tracking down the source of an internal leak, but still takes time and careful attention to detail. In addition, records regarding fluid level measurements may be of assistance during this process.

Internal Leaks:

As the name implies, internal leaks take place within the hydraulic system. Some of these leaks are intentional and take the form of narrow pathways or small orifices that allow hydraulic fluid to fly from an area of high pressure to an area of low pressure in order to cool or clean specific components. In this instance, the leak should never cause the fluid to exit the hydraulic system. However, problems can arise in the system and cause internal leaks that increase to the point that they negatively impact system performance.

One of the most obvious signs of an internal leak is a drop in system performance and efficiency. This is often accompanied by reduced reliability and lower efficiency, all of which will grow worse over time.

When it comes to internal leaks, diagnosis often involves installing flow meters in various locations throughout the hydraulic system to narrow down where the leakage is taking place, bench testing in connection with hydraulic cylinders and control valves, temperature measurement and/or ultrasonic detection.

The most common causes of internal leaks include:

  • Wear of component surfaces: as the surface of certain components begins to wear away, there is additional volumetric space for fluid to pass by these components, thus resulting in higher internal leakage.
  • Poor system design, including incorrect control tolerances during initial manufacture or rebuilds.
  • The use of incorrect parts.
  • Excessive clearance between components, which leads to a significant loss in volumetric efficiency (also known as “slippage”).


Beyond the obvious financial cost of reduced fluid levels, there is also the potential for environmental damage or employee injury. If a leak is due to a failed seal then there is the possibility that dust and moisture can begin to contaminate the remaining hydraulic fluid.

Unintended internal leaks, whilst perhaps not as messy, are just as serious. Reduced performance, less efficiency, and reliability issues can all be a result of internal leaks. Whether a leak is internal or external, it must be addressed without delay. Even though the downtime for finding and repairing a leak may seem cost-prohibitive, it will save money in the long run.

Our skilled technicians at Hydraulic Distributors can track down the source of a leak no matter how elusive it may seem. Our team can further address the issues causing that leak so that it does not reoccur. Contact us today to find out how we can help your system achieve peak performance.

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