When should the hydraulic oil be changed?

Hydraulic systems are at the heart of many machines and devices, from industrial presses to construction equipment. The oil that transmits energy within the system can be compared to blood, which plays a similar role. Regular oil changes are essential for the efficiency and longevity of the entire system. How can you tell when an oil change is necessary? What are the benefits of proper maintenance?

Regular oil changes

Hydraulic oil acts like blood in the system—it transfers energy, lubricates moving parts, and helps maintain the proper operating temperature. Over time, however, it degrades, accumulates contaminants, and loses its properties. If it is not changed at the right times, it can lead to:

• Reduced performance: contaminated or worn-out oil can reduce the efficiency of cylinders or pumps.
• System damage: contaminants can damage delicate system components.
• Increased operating costs: a system failure can result in costly repairs and downtime.

When should hydraulic oil be changed?

The first step in determining when to change the hydraulic oil is always to check the manufacturer’s recommendations for the machine or system. These may specify the time or operating hours after which an oil change is necessary. These recommendations may vary depending on the specific system and operating conditions.

Signs of oil degradation

Over time, hydraulic oil loses its properties. It is worth paying attention to:

• a change in color

• change in odor
• change in consistency

The oil becomes dark, thick, and has an unpleasant odor—similar to a burnt smell.

Symptoms indicating oil degradation:

• Worn-out oil causes an increase in operating temperature. The system overheats, which means the oil is no longer fulfilling its cooling function.
• Decreased performance or increased noise. This manifests as slower operation of actuators or pumps and higher noise levels.

The most precise method for assessing the condition of hydraulic oil is analysis. Laboratory testing of oil samples can detect the presence of contaminants, excessive wear, and other indicators of degradation. Regular analyses help optimize the replacement schedule and detect problems before they lead to a major failure. But who takes the oil to the lab? Probably very few people. An experienced machine operator will notice all of this while working. Drops in efficiency are noticeable if you know your machine and its capabilities.

Types of hydraulic oil contamination

• Water: Water enters the hydraulic system due to carelessness, damaged seals, or condensation. As is well known, oil and water do not mix—and in a pressurized hydraulic system, they cause foaming and cavitation. Water will also clog filters, reduce lubrication, and cause corrosion.
• Aeration: Aeration occurs when air enters the system through seals and fittings or during maintenance. Air trapped in the system can lead to cavitation, causing slow or no hydraulic response. Oxidation can increase viscosity, form deposits, deplete additives, and increase the oil’s acidity.
• Cavitation: This is the formation of air bubbles resulting from a sudden change in fluid pressure. Fluid flow properties deteriorate, causing pressure and flow instability. It causes micro-corrosion and significantly shortens the pump’s service life.
• Overheating: When hydraulic oil overheats, oxidation increases. 

How to properly change hydraulic oil

Before proceeding with the change, it is advisable to secure the system to prevent accidents and damage. You must obtain the appropriate amount of oil, preferably as recommended by the manufacturer, and purchase new filters. Check the condition of the hoses and seals to replace them if necessary. When changing the hydraulic oil, keep the following steps in mind:

• Drain the old oil according to the manufacturer’s instructions.

• Thoroughly clean the reservoir and remove any sediment.
• Refill with fresh oil.

When changing the oil, you must also replace the oil and air filters and check the entire system for leaks. Changing the hydraulic oil is an essential part of maintaining any hydraulic system. Regularly checking its condition and following the manufacturer’s recommendations can significantly extend the service life of your machines and minimize the risk of costly breakdowns. When inspecting the oil, look for signs of wear and don’t forget to change it at the appropriate intervals.