In a hydraulic system, changing the hydraulic fluid may seem like a simple task. But if you don’t change it properly, it can bring leaks, contamination, and even system failure. This article will help you do the job right by explaining when you really need to change the oil, what you need to prepare before you change the oil, and how to change the hydraulic oil without increasing the risk.
When to Change Hydraulic Oil？
In industrial hydraulics, you can’t just change the hydraulic fluid based on the length of use. The aging rate of hydraulic fluid varies greatly between equipment, loads, and working environments. So you should take into account the actual operation of the equipment, as well as the current performance of the fluid and the system, to determine whether you need to change the hydraulic fluid.
Operating Conditions That Cause Hydraulic Oil to Degrade
The rate of aging of the hydraulic fluid depends greatly on the operation of the equipment. The following operating conditions will accelerate oil deterioration:
Operating at high temperatures accelerates fluid oxidation, causing additives to be consumed more quickly, which reduces the effectiveness of lubrication.
Prolonged operation of the system under high loads increases friction between internal components, causing rapid degradation of fluid performance.
Frequent starts and stops can cause repeated changes in pressure and temperature, making the fluid more susceptible to deterioration and air bubbles.
In dusty, high-humidity environments, more dust and moisture will enter the system, which can damage the quality of the fluid.
Signs That Indicate Hydraulic Oil Needs to Be Changed
The hydraulic fluid and system will also give some signals to help you determine if the fluid needs to be changed.
Changes in the state of the fluid:
- If the oil color becomes dark or cloudy, it means the hydraulic fluid has aged.
- If the hydraulic fluid has an odor, the fluid may be oxidized or contaminated.
- If the foam increases and dissipates slowly, indicating that the performance of the fluid is declining.
- If there are impurities or contaminants in the fluid, it will also affect the normal operation of the system.
Changes in system operating performance:
- If the system becomes noisier during operation, internal friction or contamination is increasing.
- If the actuator action becomes slow or erratic, the fluid may be deteriorating.
- If the pressure fluctuates greatly, the fluid or system has developed an abnormal condition.
You need to note that when the above phenomena occur individually, it doesn’t necessarily mean that you have to change the oil immediately, but if multiple signals occur at the same time, you need to check the fluid and the system carefully, and then decide whether or not to change the oil.
What to Prepare Before Changing Hydraulic Oil？
Preparation before an oil change determines whether the entire operation goes smoothly, and also affects the safety of the system and the life of the fluid. You need to focus on three things: oil selection, tools, and contamination control.
How to Choose the Right Hydraulic Oil for Your System？
The viscosity of the hydraulic fluid should be consistent with the viscosity grade recommended in the system manual, lubrication and system efficiency will be reduced.
The hydraulic fluid must meet the standards specified for the system or equipment. You can check the equipment manual or the manufacturer’s technical data to confirm which specifications the oil meets.
Different types of oil may not be compatible. So, before changing or adding new oil, you should check the manual or ask the supplier if the new oil and the old oil can be mixed.
Tools and Cleanliness Required for a Hydraulic Oil Change
Before changing the hydraulic oil, you need to prepare tools such as a draining device, a drum, a funnel, gloves, and cleaning rags.
You should clean all containers and tools before changing the oil to avoid dust, moisture, or impurities entering the hydraulic system.
The operating environment should be clean, dry, and at the right temperature to reduce the risk of contamination and operational errors.
During operation, you should not touch the fluid directly to avoid bringing dust or moisture from your hands into the system.
Preparing your tools will make the oil change process go smoothly. Keeping the operating environment clean protects the hydraulic system and extends the life of the fluid and equipment.
Step-by-Step Guide to Changing Hydraulic Oil
The following steps apply to most industrial hydraulic systems. For specialized systems, you can follow the equipment manual or professional recommendations.
Step 1: Shut Down the System and Release Hydraulic Pressure
Before you start changing the oil, you must shut down and completely relieve the hydraulic system.
You want to keep the oil temperature within safe limits to avoid scalding yourself or damaging system components with hot oil.
Shutting down and relieving pressure prevents the system from taking an unexpected shock during an oil change and protects you as well.
Step 2: Drain Hydraulic Oil Without Causing Contamination
When draining the fluid, you should follow the order in which the system is designed to make sure you drain the old hydraulic fluid.
When operating, you should control the speed of the discharge to avoid contamination of the system by dust and moisture.
After draining is complete, you should wipe the ports with a rag to prepare them for the addition of new oil.
Step 3: Replace and Inspect Hydraulic Filters
When you change the fluid, you should check and change the filter element at the same time.
By looking for contamination in the cartridge, you can determine if there is a potential contamination problem in the system.
A clean filter element protects the new oil and the system, extending the life of the equipment.
Step 4: Refill Hydraulic Oil and Remove Air
When filling with new oil, you should add it slowly and evenly to avoid air bubbles or disturbed deposits.
You should not refuel only according to the amount of oil discharged, but rather according to the oil level gauge or tank scale.
After refueling is complete, you should start the system and exhaust the air to make sure that no gas remains in the hydraulic circuit.
What to Check After Changing Hydraulic Oil？
Do not leave the unit immediately after an oil change. Many problems occur after an oil change.
Here are some places to focus on checking:
- After the equipment is started, you should check if the oil level is normal and refill the oil properly if necessary.
- You should listen to the system for abnormal noise.
- You should pay attention to whether the action of the actuator is smooth.
- You should check whether the pressure is stable.
- You should look to see if the system is leaking oil, especially at the locations of the drain and fittings.
- You should watch for the oil to foam heavily or become muddy.
- You should check the system several more times during the first few hours of operation. If you find more than one abnormality, you should immediately shut down and recheck the oil level, filter element, and operating procedures.
- Just because an oil change is complete does not mean maintenance is over. The oil change is not truly successful until the system is running stably.
Common Mistakes When Changing Hydraulic Oil
Changing hydraulic fluid isn’t complicated, but many problems are caused by ignoring details. Here are a few of the most common mistakes.
Changing Oil Without Inspecting the System
Some people just drain the old oil and add new oil without checking the condition of the system.
If there are contaminants in the system, a clogged filter element, or worn parts, just changing the oil won’t solve the problem.
Sometimes the oil looks fairly clean, but it may have oxidized or run out of additives, changes that are not visible to the naked eye.
That’s why you can’t tell if you need to change the oil just based on the color of the oil, but also on the operating condition of the system.
Contaminating New Oil During Refilling
Many problems are not caused by old oil, but are brought in when new oil is added.
If the refueling bucket is not clean, the oil is left open for long periods of time, and the funnel is dusty, contaminants can enter the system together.
It’s also easy to bring contaminants into the system if the surrounding environment is dusty when refueling.
This step is critical because all of the previous efforts to drain and clean the oil can be destroyed during refueling.
Ignoring Reservoir, Breathers, and Sealing Components
Some people focus on the oil but ignore the tank, breather, and seals.
If the tank is not cleaned out, the new oil will soon become contaminated with old deposits.
The breather is there to filter the air. If it breaks down, dirt will go straight into the system.
Seals that are deteriorated can allow water or dust to enter the system, which can also lead to oil leaks.
These parts are insignificant, but they can affect the cleanliness of the fluid and the stability of the system.
Changing Hydraulic Oil When the System Is Not Suitable
Not all hydraulic systems are suitable for self-service oil changes.
If the system requires extremely high levels of cleanliness, even small amounts of contamination can affect its operation.
If the system is complicated, old oil may not be fully drained, leaving contaminants trapped inside.
If the equipment stops working and causes big losses, it might be safer to let customers change their own oil.
If the temperature or pressure is wrong, it can be dangerous.
In these cases, changing the oil without knowing what’s going on is a bad idea.
FAQ
Do I have to change all the filter elements when I change the oil?
In most industrial hydraulic systems, it is recommended to change the filter elements at the same time as the oil change.
Contaminants and metal particles have usually accumulated in the old filter element. If they are not replaced, the new oil will soon become contaminated.
If the cartridges have been in use for a short period of time, you can decide whether or not to replace them depending on the contamination, but it is usually not recommended to skip this step.
Will a little old oil left in the system affect the new oil?
A small amount of old oil left in the system does not usually cause an immediate problem.
However, if the old oil has become heavily oxidized or contaminated, it can cause the new oil to deteriorate at an accelerated rate.
If the system is heavily contaminated, you should evaluate whether to perform a hydraulic system flush instead of just changing the oil.
Can I use different brands of hydraulic fluids of the same viscosity together?
Hydraulic fluids of the same viscosity grade cannot be safely mixed.
Different brands of hydraulic fluids may have different additive formulations that may affect oxidation or foam resistance when mixed.
Before mixing, you should check the technical data or consult your supplier to make sure the fluids are compatible.
If you can’t confirm, don’t mix.
How often is it reasonable to check the hydraulic fluid?
The frequency of inspection depends on the importance of the system and the operating conditions.
Ordinary industrial equipment can have a fluid check every 3 to 6 months.
High-load or critical production equipment can be inspected every 1 to 3 months.
If the environment is highly polluted, you should increase the inspection frequency.
What do I need to pay special attention to when I change the oil in very cold weather?
Cold temperatures make the hydraulic oil thicker and less fluid, so you can’t get the old oil out completely.
You can run the equipment for a short period of time before changing the oil, so that the temperature of the oil rises to a state suitable for flow before changing the oil.
At the same time, you need to avoid condensate entering the hydraulic system to prevent moisture from contaminating the new oil.
How long after an oil change can I run the system normally at full load?
Do not run the hydraulic system at full load immediately after changing the oil.
You should first let the system run at low load to check if the oil level and pressure are normal and if there are any leaks in the system.
If the operation is stable and there is no abnormal noise or pressure fluctuation, you can then gradually return to normal load.
Are oil changes the same for small and large industrial equipment?
The basic principles are the same, but the risks and complexities are different.
Small systems are simple in construction and relatively easy to drain and refuel.
Large industrial systems have complex piping and a higher risk of system contamination.
Larger systems require stricter contamination controls and more detailed operating procedures.
Final Thoughts
Changing hydraulic oil may seem common, but if you don’t do it right, the system can easily break down. You should combine the operation of the equipment and the state of the oil to determine whether you should change the oil. You should prepare the oil before changing it, control the contamination when changing it, and check it carefully after changing it. Get every step right, and the system will be more stable.
With over 10 years of experience in industrial hydraulics, Target Hydraulics can provide you with hydraulic fluid change recommendations, system contamination control programs, and hydraulic component selection support. If you want to make your system safer to operate, feel free to contact us.
