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How to Check Hydraulic Oil Level on an Excavator

Yellow excavator with large bucket and hydraulic oil hoses

Checking the hydraulic oil on an excavator is a simple, yet important task that should be performed each day as part of the routine maintenance checks prior to operating an excavator or other hydraulic machinery.

Checking the hydraulic oil on an excavator is fairly straightforward, even for a beginner and the steps involved include ensuring the machine is cold and parked on a firm, level surface. Additionally, the boom and bucket must be positioned in accordance with manufacturer instructions to ensure an accurate reading. From there it is generally a matter of locating the hydraulic oil tank and ensuring the oil level is between the minimum and maximum marks on the oil sight glass.

Various Types of Excavators

There are some differences between the various makes of excavators:

  • Kobelco excavators, for example, will require the operator to ensure all cylinders are retracted including the bucket cylinder to ensure maximum amount of oil is in tank.
  • Hitachi excavators on the other hand, will require the operator to do the above, with the exception of the bucket cylinder, which needs to be fully extended and placed on the ground prior to checking the oil level.

Kobelco excavator logo/ Hitachi excavator logo

Again, highlighting the difference between the two:

  • The sight glass on a Kobelco excavator will typically be visible through the cab window
  • On a Hitachi, the access door to the main pump will need to be opened to view the sight glass.

If in doubt as to the correct way to check the hydraulic oil on a particular excavator, always consult the user manual, which is commonly found in the back pocket of the operator’s seat.

General Safety Precautions

General safety precautions include removing the key from the ignition before checking oil as well as ensuring there is no pressure in tank, prior to removing the hydraulic oil cap in the event of it needing to be topped up.

Obviously as an owner/operator, the incentive is to ensure the longevity of your investment. But even purely as an operator, it is in the operator’s best interest to ensure a thorough pre-start check is carried out prior to use, to avoid being liable for pre-existing damage to the machine, or in the case of rental equipment – being blamed for neglecting to carry out mandatory checks listed in the rental agreement.

Grades of Hydraulic Oils

There are a number of hydraulic oils on the market, ranging from hydraulic oil used in excavators, right through to food-grade oil found in food processing plants. The most common hydraulic oil types for excavators are 46-grade and 68-grade oil. The numbers refer to the viscosity of the oil. The easiest way to remember it is: the lower the number, the thinner the oil. As a rule, whatever oil grade is specified by the manufacturer, is the one to go with.

Hydraulic Oils vs Motor Vehicle Engine Oils

Hydraulic oil differs from motor vehicle engine oil in a number of ways:

  • Firstly the purposes of these two oil types are inherently different. Hydraulic oil’s primary function is to convey power in hydraulic machinery whilst in a 4 stroke engine, the main purposes of the oil are to lubricate, quieten and cool the engine.
  • Engine oil contains a lot of additives required to combat contaminants as a result of the combustion process. In theory many engine oils would function in a basic hydraulic application, but hydraulic oil would not have the ability to protect an engine.

“As a rule, whatever oil grade is specified by the manufacturer, is the one to go with.”

Function of Hydraulic Oils

As mentioned above, hydraulic oil is required in an excavator as it is the medium by which power is conveyed. Every action you observe an excavator doing is hydraulically operated. Excavators are able to track forwards and backwards by the means of a left and right hand hydraulic track motor which receive oil from the main oil pump which is connected to the diesel engine. A hydraulically powered slew motor allows the excavator to swivel around 360 degrees, whilst the boom, stick, and bucket are all operated by cylinders connected to the main hydraulic circuit. Buckets can also exchanged for various hydraulic attachments depending on the task at hand. These include hammers, augers, and grabs, to name a few.  

Prices of Hydraulic Oils

There are many different hydraulic oil brands on the market, at varying prices. As hydraulic oil is a relatively minor percentage of the overall maintenance costs on an excavator, it does make sense to pay for quality oil. If not buying directly from the dealer, at least ensure that it is a recognized brand and that it meets the manufacturer’s specifications. As the saying goes: Cheap oils are more expensive in the long run.

Lifespan of Hydraulic Oils

Hydraulic oil does deteriorate over time. One of the greatest factors affecting the life of hydraulic oil is the overall operating temperature of the oil. But seeing as there additional variables in play to determine at which point hydraulic oil requires changing, the safest and most logical option is to stick with the (usually conservative) intervals listed in the machine handbook by the manufacturer. In theory, if the hydraulic oil is well filtered, is not contaminated by moisture, and is operated at a relatively cool operating temperature, it could in all likelihood far exceed manufacturer recommended intervals. However, the average owner/operator might not be aware of the options available when it comes to the cost of regular, in-depth oil analysis, compared to routine hydraulic oil changes.  

Oil Levels

It is important not to overfill the oil on a hydraulic system as this will not allow for oil expansion, causing oil to leak out of the breather or filler cap. A low oil level in a hydraulic system is usually an indication of a leak somewhere that needs to be addressed. Running a hydraulic system with little to no oil can damage the hydraulic pump and other internal components. An obvious sign of low oil when operating an excavator is loss of hydraulic function which may be caused by something as simple as a blown hose.

Hydraulic Hoses

Aside from the usual wear and tear hydraulic hoses encounter through repeated movement and exposure to the elements such as UV rays, a common cause of hose failure is incorrect installation or routing of the hose. Installing a hose with a twist in it of only 7 degrees can drastically reduce the hose life by as much as 80%. 

Additionally, failing to route a hose correctly can cause it to rub against other hoses, mountings or components, leading to premature wear of the outer cover and eventual failure of the hose itself. To ensure maximum hose life, always ensure that hydraulic hoses are the correct pressure rating, that fittings are tightened correctly and that hoses are secured properly through the use of clamps, ensuring that any bends in the hose do not exceed the maximum bend radius specified by the hose manufacturer.

“Installing a hose with a twist of only 7 degrees can reduce the hose life by as much as 80%”

Hoses and oil fittings coupled to an engine


In addition to the safety factors touched on earlier, there are other safety aspects to keep in mind when checking, changing or filling oil:

  • If a leak is suspected, never run your hands along hoses or components in search of the leak to avoid the risk of fluid injection injury.
  • Use other, safer means to identify potential leaks such as a mirror if you are unsure of the location of a hydraulic leak, along with the appropriate personal protective equipment such as glasses and gloves.
  • Potential hazards when filling oil include the manual handling aspects of lifting and carrying hydraulic oil containers.
  • Another important safety aspect when working on or around excavators is to maintain positive communication with people around you. Never assume anything.
  • When checking oil for example, make sure the machine is not able to be started and operated. Standing within the slew radius of an operating machine can have disastrous consequences.  

If unsure of the hydraulic oil level of an excavator due to a cloudy sight class, or poor lighting, always double-check. This might mean physically removing the hydraulic oil cap on the tank to confirm the level is correct. Taking the time to ensure oil levels are correct is an important element of good maintenance routines.

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The above information is a general guide only. Always consult the operator’s manual relevant to your specific machine and use the recommended oil. Hydraulic systems on excavators operate at high pressure and any repairs should be carried out by a qualified technician.