Our customers often give us feedback that the hydraulic system of marine cranes will have various problems after long-term use, and OUCO reminds you that in the daily use of cranes, you should not neglect the detection and maintenance of crane hydraulic oil. Want to know more about hydraulic oil related issues? Please read this guide.
What is the function of hydraulic oil?
Hydraulic oil is an excellent working medium. What’s more, hydraulic oil enables energy transfer, conversion and control.
Hydraulic oil can lubricate mechanical components, prevent internal rust, cool down, buffer and shock absorption, etc.
Why should I do hydraulic oil maintenance?
Hydraulic systems need very clean hydraulic oil for maximize performance.
High-quality hydraulic oil can maintain and extend the life of system components.

When should I change the crane’s hydraulic oil?
The deterioration of hydraulic oil is not always visible from the outside. Therefore, the quickest way to identify a problem is to observe the performance of your crane. If it is becoming less efficient and struggling to lift properly, it may be time to change the hydraulic oil.
In addition, the following situations also need to be noted:
- Marine crane hydraulic oil aging, which will lead to hydraulic oil emulsification and deterioration, the aging hydraulic oil needs to be replaced on time.
- Marine crane hydraulic oil tank additives depletion needs to be replaced, such as antioxidants, rust inhibitors, cleaning agents, anti-foam agents, etc.
- The viscosity of hydraulic oil increases, the speed of the hydraulic motor decreases, and the movement of the crane boom becomes slower.
- The pressure of the hydraulic system decreases and the components leak.
- The sound of the gear pump is abnormal, and the parts often need to be replaced.
- Carry out hydraulic oil tests every year to ensure that the quality of hydraulic oil is within the normal range. If the test fails, it needs to be replaced.
To avoid constant concern about the condition of the hydraulic oil, consider using an automatic lubrication system. This system monitors the operating status of the equipment and ensures that oil is delivered to each lubrication point in a timely, accurate and automatic manner.

Crane hydraulic oil service life?
- After purchase, the first replacement needs to be about six months after use, this is to prevent impurities generated in the hydraulic component break-in and solid particles in the pipeline, which will flow back to the tank with the hydraulic oil.
- In normal use, it needs to be replaced once a year. Of course, you can also adjust yourself according to your frequency of use. However, it should be noted that the general use period of mineral hydraulic oil should not exceed two years.
- Synthetic hydraulic oil can be used for up to three years if it passes the test every year.
How to change the hydraulic oil correctly?
There are many users who do not follow the requirements of hydraulic oil replacement, non-standard replacement methods will lead to the failure of the marine crane. It is a mistake to simply drain the hydraulic oil tank and subsequently fill it with new hydraulic oil.
If the hydraulic oil pipe and control valve are not thoroughly cleaned, remnants of the old hydraulic oil can linger. When the crane is operated, this old oil mixes with the new, accelerating the deterioration of the fresh hydraulic oil.
The correct oil change steps are as follows.
- Hydraulic oil need to ensure the use of the specified type of hydraulic oil, you can refer to the hydraulic oil guide and our related documents.
- Drain the hydraulic oil in the hydraulic oil tank, clean or replace the filter element, wash the oil tank and add new hydraulic oil.
- Remove the hydraulic oil circuit main hose, turn on the engine and run at low speed to make the oil pump work
- Manipulate each institution separately, and then disassemble the return hose of each working cylinder, and completely discharge the old oil in the circuit through the new hydraulic oil, until the return main hose has new oil outflow.
- Finally, connect the oil return hose to the oil tank, and add new hydraulic oil into the tank to reach the specified position.
- Run the machine for a period of time and then repeat the process several times to gradually replace the residual old oil.

What should I pay attention to in the process of changing hydraulic oil?
- During the oil change work, wear protective glasses, turn off the motor and the main power of the equipment
- New oil should be precipitated for more than 48 hours before use
- Must use silk cloth, strictly forbidden to use cotton yarn, towels and other fiber fabric to wipe the parts
- Post the time mark, fill in the oil change record
- Operation site, the presence of open fire is strictly prohibited
- The oil change process is completed on the same day to avoid temperature changes in the morning and evening
What are the hydraulic oil requirements for marine cranes?
- The oil should have suitable viscosity and good viscosity-temperature performance
- Good rust resistance, oxidation resistance, hydrolytic stability
- Non-flammable, shear resistance
- Suitability with hydraulic sealing components and hydraulic tank materials
- Hydraulic oil with wear resistance and lubricity
- Good anti-foaming property, so that the hydraulic oil can keep normal under continuous mechanical agitation
What hydraulic oil is used in marine cranes?
Hydraulic oil grade distinction according to the viscosity decision, marine cranes generally use 46 or 68 hydraulic oil.
46 hydraulic oil viscosity is less than 68 hydraulic oil, 46 hydraulic oil is suitable for year-round use in temperate regions, and 68 hydraulic oil is suitable for subtropical.
Also, if you need to use it in cold areas, we recommend you use hydraulic fluid 32 because of its lower viscosity.
In addition, there are 68, 100, etc., different grades are suitable for different equipment and machines, you can choose the corresponding hydraulic fluid according to the viscosity grade recommended by the supplier.
How do I know if I need to refill my hydraulic oil?
Observe the hydraulic oil level gauge. When the hydraulic oil has been filled, the oil level will be at the red mark in the picture.
When the oil in the tank is below the marked scale in the picture, the hydraulic oil needs to be replenished and filled.
What is the classification of hydraulic oil?
Hydraulic oil is classified into HH type, HL type, HM type, HR type and HG type
What is a hydraulic oil air cooler?
Hydraulic oil cooler products are mainly used in the return path of the hydraulic system. When working, the high temperature hydraulic oil in the hydraulic system will pass through the hydraulic oil cooler device, and the cold air will reduce the oil temperature to the working temperature required, to ensure that the machinery and hydraulic system can operate normally.

OUCO offshore crane can be equipped with hydraulic oil air cooler according to your needs, our hydraulic oil air cooler flow pipe is arranged as shown below, so that the arrangement of the flow pipe can make the hydraulic oil flow pipe surface is larger and the cooling effect is better.

Can I mix hydraulic oil?
Try to avoid mixing hydraulic oil! If you are about to run out of hydraulic oil, it is best not to add other hydraulic oil to fill the hydraulic oil tank, different brands of hydraulic oil, they contain mostly different additives, these additives may affect each other, resulting in adverse consequences.

What is the difference between lubricating oil and hydraulic oil?
The main function of lubricant oil is to reduce friction, slow down wear and prevent metal sintering.
The hydraulic oil viscosity is more important. Hydraulic oil needs to perform well at high temperatures and low temperatures, to ensure that the oil flows easily and reduces energy consumption.
In addition, they are not interchangeable. If you use hydraulic oil as a lubricant oil, it is difficult to form a protective oil film on the machine surface, which will increase the wear of the machine. Therefore, hydraulic oil is not suitable to be used as a lubricant oil replacement in your machine.
Summary
The above is the hydraulic oil guide for your reference. I believe that after reading the above content, it will be of great help to you.
Also, remember that if you encounter a problem that you cannot solve yourself, do not hesitate to contact your product’s hydraulic oil supplier immediately.
Finally, if you have the need of offshore knuckle boom crane, telescoping crane and other lifting equipment, OUCO will be your reliable partner!
Recommend Reading:
How to change the hydraulic oil of the remote control grab?


