Skid steer loaders and compact track loaders are among the most versatile pieces of equipment on the market today. That versatility stems from the heart of these machines — their hydraulic systems. The hydraulic system is used to drive the machine, operate the loader and attachments, provide dynamic braking and lubricate components. It is even used to cool many of the components. A fair share of maintenance cost is centered on the hydraulic system. Proper maintenance and care of skid steer loader hydraulic systems is crucial not only for the longevity of the machine, but also for keeping costs and downtime to a minimum.
While many brands of skid steer loaders and compact track loaders may appear similar and have similar components, there can be differences in how to service their hydraulic systems properly. It’s very important to review your owner/operator’s manual before attempting to perform any maintenance to the hydraulic system, taking special care to review the safety procedures listed in the manual. Hydraulic systems in skid steer loaders can be rather complex in newer machines. There can be as many as five or six hydraulic pumps within the system. With the variety of options available today such as high flow, bucket self-leveling, ride control and hydraulic quick-attach brackets, there may be up to five or six control valves as well. All of these components are designed with very tight tolerances which may fall below 0.001 in. Because of this, keeping the hydraulic system clean is critical to the life of these components. Contamination is the single biggest reason hydraulic components fail and most of the time, it can be prevented.
Contamination may enter the system in a variety of ways. Perhaps a hose was recently replaced or maybe an operator neglected to clean the area around the tank’s fill spout before the system was topped off. Before removing the hydraulic oil reservoir cap, clean the area around it to prevent dirt from entering the tank. Additionally, if you fill the hydraulic system using a bucket, make sure that there is no loose dirt on the lid of the bucket that could fall into the tank. While all machines will have at least one hydraulic filter to remove debris from the system, this filter might be in the return side of the hydraulic system. This means that any dirt that enters through the reservoir may be sucked through the pumps and valves before it’s caught in the filter. There is a screen inside the tank to prevent large material from getting into the pumps, but it won’t catch small particles.
Another common way for contamination to enter the hydraulic system is by using hydraulically powered attachments. Before connecting any of the auxiliary hoses, be sure to wipe off the connectors to get rid of any water, dust or other debris. If a component such as a motor on a broom or auger fails, pieces of metal may enter the hydraulic system and cause damage. If an operator notices that an attachment isn’t functioning properly, a dealership or service personnel should be consulted before continuing its use. It’s much cheaper to fix just an attachment rather than having to fix a skid steer loader as well because of a broken attachment contaminated the hydraulic system. Lastly, if an attachment was used on a skid steer loader that had a hydraulic failure and spread contamination into the attachment, that contamination may enter the next machine it’s connected to. After repair, be sure to flush contamination out of the attachment before use on another machine.
In order to further prevent contamination, make sure to follow the OEM’s service interval for hydraulic filter replacement. This may fall anywhere between 500 to 1,000 hours depending on manufacturer and operating conditions. A plugged up hydraulic filter may cause a variety of issues such as loss of speed or power, overheating of the hydraulic oil and damage of components. It is also highly recommended to use OEM filters. While you may find filters cheaper elsewhere, OEM filters are specifically designed to clean the hydraulic oil with the most efficiency within that particular system. They are designed to allow a certain amount of flow and pressure through the filter material. Using filters other than the OEM’s may change the flow, which can make the machine perform differently.
What type of hydraulic oil should be used in a skid steer loader? This is a very important topic that is frequently overlooked. You should always review the operator’s manual for the skid steer loader before using any kind of oil in the hydraulic system. There will generally be two or three different options, mostly dependent on the climate that the machine will work in. It is strongly recommended to use the OEM oil recommended within the owner’s manual or equivalent. Components within the system are designed to function properly with a certain viscosity and chemical formula of hydraulic oil. Many times there are various additives within the oil to prevent water absorption and cavitation. The oil must also be compatible with the sealing material throughout the system such as O-rings and cylinder packing. Lastly, make sure when topping off the system that the same oil is used that is already in the machine. Mixing different hydraulic oil may cause a variety of issues such as loss of lubricity or component damage.
Just as important as the type of hydraulic oil used is the amount in the tank. The operator’s manual will show where the level should be within the sight glass and where the boom and bucket should be located while checking the hydraulic oil level. Most machines should be checked on a level surface while having the boom all the way down and the bucket flat on the ground. There may be multiple lines within the sight glass and they could be for checking the oil while it is cold or while the oil is at operating temperature. Those lines might also refer to a minimum and maximum level. If the hydraulic level is too low, damage to the hydraulic pumps may occur or the oil may overheat. If the level is too high, the tank may overflow when the oil heats up due to expansion.
Hydraulic oil should be checked daily, if not before every time the machine is operated. If the level is low, look around carefully for leaks. Given the dusty and dirty conditions that skid steer loaders and compact track loaders operate in, it is very common for mud, dirt, dust, grass, sticks or other debris to build up inside the machine. If there is a leak inside the machine, it may take a while for that oil to seep through all of the debris and form a puddle on the ground. Therefore, the first sign of a leak might be a low level of hydraulic oil. If you find a leaking hydraulic hose, contact an appropriate service technician or your local dealer. If you decide to replace it yourself, make sure all of the pressure is relieved from the system before removal of the hose or personal injury may result.
Because of the accumulation of debris inside the machine, the hydraulic cooler is another frequently overlooked component. This will usually be located at the rear of the machine near the radiator or in some cases even built into the radiator. The oil cooler might use engine coolant or outside air to cool the oil. It is vital that the oil remain within the acceptable operating temperature range. Make sure the oil cooler is free of debris and the cooling fins are fairly straight. If airflow can’t pass through the cooler, the oil will overheat causing issues within the hydraulic system.