Overfilling Hydraulic Fluid Can Cause Issues, Too

Low levels of hydraulic fluids can harm systems and result in poor efficiency, but they are often monitored and remedied quickly.

But what about overfilled hydraulic fluid?

Too much hydraulic fluid might also cause damage such as:

• Messy leakages
• Smoke or fires
• Wear of components

Most importantly, however, high fluid levels could disrupt flow, an action needed to transfer energy through a hydraulic system.

Fluid flow cools system components, lubricates surfaces, removes contaminants, and can seal running clearances to minimize internal leakage.

Speaking of flow, lubricant engineers also know the value that oil viscosity has on petroleum-based hydraulic oil levels.

Just as low fluid levels are often considered, viscosity is often given considerable attention. Viscosity has a significant impact on the operation of a hydraulic system.

Low oil viscosity can cause a loss of?lubricating film strength?leading to wear between two parts. High oil viscosity can cause problems like heat generation and?cavitation.

Selecting the right fluid?viscosity, which is the measure of a fluid’s resistance to flow, is necessary to protect equipment from:

• Friction
• Abrasion
• Poor Mechanical Efficiency
• Adhesive hydraulic component wear

But there’s a case to be made that reservoir selection and subsequent fluid levels are also important for system flow and efficiency and that steps to remedy overfilled fluids are just as necessary as other mechanical issues.

Fluid levels are important to consider when maintaining the health of hydraulic systems. And not just low fluid.

The Importance of Reservoir Size and Fluid Levels

In a hydraulic system, reservoir size is the key to operating efficiently by providing a steady supply of fluid that allows de-aerated fluids to rise and escape while solid contaminants settle to the bottom of the reservoir.

The first variable to resolve when sizing a hydraulic reservoir is determining volume.

The volume of a hydraulic reservoir should be three times the rated output of the system’s fixed-displacement pump. For example, a system using a 7-gpm pump should have a 35-gallon reservoir.


The proper level in the reservoir will provide adequate space to give off trapped heat and non-condensable gases while reducing return line head pressure, allowing the fluid returning to flow at the proper feet per second.

In short, a properly sized hydraulic reservoir (when filled to the proper level) should provide adequate volume for:

• Heat transfer
• Dissipation
• Contaminant settling
• Deaeration
• Gravity drain-back from a system during shutdowns
• Storage of large volumes needed intermittently during peak periods of an operating cycles
• Mounting other system components

What if Fluids are Overfilled?

The quick answer to this question is to clean up any leaks and get the system running at the correct level using siphons, pumps, or a variety of reservoir accessories.

There are?several reservoir accessories?available, which can be used for:

• Indicating fluid level in the reservoir
• Indicating fluid temperature
• Routing return fluid to minimize potential pump cavitation and improve heat transfer
• Heating cold or low-viscosity fluids to necessary operating temperature
• Removing ferrous contaminant particles from the fluid

Two examples of accessories that can help avoid fluid level mistakes and flow issues are flow diffusers and fluid-level indicators.

Flow diffusers slow fluid returning to the reservoir, reducing foaming and pump cavitation from flow disturbances at the inlet, and providing fluid mixing without agitation. They are especially effective in small reservoirs with high flows and in deep reservoirs with a small floor area.

Fluid-level indicators can be installed with high and low levels marked against a contrasting background to help maintain appropriate fluid level. Electronic level indicators can automate this action.

HPS provides support for part needs with a massive library of product literature and help from our product experts.

Avoid Overfilling to Keep Hydraulic System Running Smoothly

There are two fundamental?considerations?in hydraulics: the type of hydraulic oil and the degree of viscosity.

Considerations include base oil type, lubricant quality, and execution characteristics, such as overfilling and reservoir size.

And if execution mistakes are made, there are plenty of accessories that can help avoid or fix them in the future.

Overfilling fluids may not lead to the problems these fundamental considerations can create, but should nevertheless be considered to run an efficient hydraulic system.

Hydraulic Parts Source is a leading fluid power remanufacturer, and we’re ready to serve you. Contact us today to experience OE quality for a fraction of the time and cost by calling (888) 477-7278 or get a quote by emailing sales@hydparts.com.