Your Bobcat S590: Pressure, Problems, and Fixes

The Bobcat S590 skid steer loader has long been a workhorse on construction sites, farms, and various industrial applications across the UK. Renowned for its robust performance, compact size, and versatility, it's a favourite among operators who demand reliability. Whether you're lifting, digging, or moving materials, the S590 is engineered to handle demanding tasks with ease. However, like any complex piece of heavy machinery, understanding its intricate systems, particularly its hydraulic pressure and common operational quirks, is paramount for efficient maintenance and longevity. This comprehensive guide will delve into the critical specifications of your S590, address frequently encountered problems, and provide actionable solutions to keep your machine running smoothly and reliably.

Understanding Your Bobcat S590's Hydraulic System

The hydraulic system is the very heart of your Bobcat S590, responsible for powering its lift, tilt, and auxiliary functions. It's what gives your skid steer its impressive strength and precision. Knowing the system's operational parameters is vital for both performance and troubleshooting. For the Bobcat S590, the hydraulic system relief pressure is a crucial figure:

• System Relief Pressure: 3550 psi (245 bar)

This pressure ensures that the hydraulic fluid is delivered with sufficient force to operate all implements and movements. Operating outside of these designed pressures, either too low or too high, can indicate a problem within the system, potentially leading to reduced lifting capacity, slow movements, or even damage to components. Regular checks and adherence to manufacturer specifications are key to maintaining this vital system.

Hydraulic Fluid: The Lifeblood of Your Bobcat

A common question among Bobcat S590 owners and operators is regarding the type of hydraulic fluid to use. While it might seem tempting to use generic hydraulic oils, there's a specific recommendation for a reason. Yes, you can technically use other hydraulic oils, but Bobcat strongly suggests using its own all-season hydraulic or hydrostatic fluid. This isn't just a marketing ploy; Bobcat's fluids are formulated with specific additives tailored to meet the exact requirements of their hydraulic and hydrostatic drive systems. These additives ensure optimal performance across varying temperatures, provide superior wear protection, and help prevent issues like foaming and corrosion, ultimately extending the life of your components and ensuring your warranty remains valid. Always consult your operator's manual for the precise fluid specifications and recommended service intervals.

Engine Evolution and Common Bobcat S590 Issues

The Bobcat S590 has seen an evolution in its engine over the years. Historically, Bobcat models, including earlier S590 variants, utilised reliable Kubota engines. However, as of 2015, Bobcat transitioned to Tier IV Doosan engines for many of its machines. This change, driven by emissions regulations, introduced new technologies and, for some users, a new set of characteristics and potential issues. While the Kubota engines were known for their robust simplicity, the newer Doosan engines, with their advanced fuel systems, require a more nuanced approach to maintenance. Many of the reported issues with the S590, particularly those related to fuel contamination and injection systems, are often associated with these more modern Doosan powerplants. Understanding these common problems is the first step towards effective maintenance and ensuring your machine's longevity.

Recognising and Resolving Performance Problems

Here’s a breakdown of the most frequently reported issues with the Bobcat S590, particularly those equipped with the Doosan engine, along with practical remedies:

1. The Machine is Lagging Power

When your Bobcat S590 feels sluggish and lacks its usual vigour, a few common culprits are often at play. Modern engines, especially those designed for Tier IV compliance, are incredibly sensitive to airflow. A frequently overlooked issue is a clogged air filter. These engines are "thirsty" for air, and when the air purifier becomes blocked, it can dramatically reduce engine efficiency and even force oil out of the motor, leading to a noticeable drop in power.

Solution: Begin by inspecting and cleaning the air filter. If it's heavily soiled, replace it. Following this, it's a good practice to replace the fuel filter as well, as a dirty fuel filter can also restrict fuel flow and impact performance. Finally, always check your fluid levels. Ensure your engine oil is at the correct level, as insufficient or contaminated oil can contribute to power issues. After these steps, your machine should regain its full engine performance.

2. The Throttle Does Not Respond

An unresponsive or delayed throttle can be frustrating, especially when precision is required. This is a fairly common characteristic, particularly in colder climates. In cold weather, the throttle mechanism can become stiff or slow to react, taking some time to properly engage and respond to operator input.

Solution: Patience is key here. After starting the engine, allow it a sufficient amount of time to warm up. Keep an eye on the "Cold" message that may appear on your LH display; this indicates the engine has not yet reached its optimal operating temperature. Once this message clears, the throttle response should normalise. To mitigate this issue during prolonged cold spells, consider storing your S590 in a heated garage or workshop overnight. This can significantly reduce the warm-up time and improve immediate throttle responsiveness.

3. The Injection Pump is Failing

The injection pumps in modern diesel engines, especially those like the Doosan units in later S590 models, are incredibly delicate and highly susceptible to fuel contamination. If the infusion compressor begins to fail or has already failed, the engine may struggle to start or run at all. This component is critical for delivering fuel at the extremely high pressures required for efficient combustion.

Solution: A quick diagnostic check involves connecting a sensor to the injector nozzle and monitoring the "desired" versus "real" rail compression. If the injection system is compromised, it will struggle to maintain the preferred motor rail pressure. Should this discrepancy be observed, the primary course of action is to thoroughly troubleshoot for fuel contamination. This might involve inspecting fuel lines, filters, and even the fuel tank itself for impurities or water.

4. The Inlet Metering Valve (IMV) is Not Working

On the Bobcat D24 and D34 propulsion systems (found in many S590 models), the inlet metering valve (IMV) is responsible for precisely metering rail compression. If this piston fails or becomes faulty, the engine will lose its ability to respond accurately to commands for increasing or decreasing rail compression, leading to erratic engine behaviour or a complete lack of power.

Solution: To quickly check the IMV, place your thumb on the valve itself and start the engine. You should feel a slight resonance or vibration as the IMV operates. If there's no vibration, or if it feels weak, the IMV could be defective, or its power cord could be faulty. Start by checking and potentially replacing the power cord. If the problem persists, then the Inlet Metering Valve itself likely needs to be replaced. This is a critical component for precise fuel delivery.

5. Fuel Injector Contamination

Bobcat Doosan D24 and D34 motors utilise Delphi's advanced, slightly elevated pressure common rail diesel plugs. These sophisticated fuel injectors are particularly vulnerable to fuel contamination, which remains the most common cause of their failure. The plugs feature extremely small diesel control valves, and even minute particles in the fuel can become embedded in the pressure regulator, causing blockages and operational difficulties.

Solution: Similar to injection pump issues, fuel injectors can also leak rail compression. Use a sensor to compare the desired and actual rail strain to ascertain if the motor is receiving adequate pressure. Injectors can bleed rail strain through the fuel exchange, or a nozzle might become stuck open. Bobcat diagnostic equipment can test the injectors to see if they respond to a pulse signal. If an injector fails to respond correctly, it indicates a malfunction, and replacement of the fuel injector will likely be necessary.

Detailed Bobcat S590 Specifications

To further assist with understanding and maintaining your skid steer, here is a comprehensive breakdown of the Bobcat S590's key specifications. These details are invaluable for ordering parts, understanding performance limits, and performing accurate diagnostics.

Engine Specifications

Drive Train Specifications

Hydraulic System Specifications

Loader Performance Specifications

Dimensions and Weight Specifications

Frequently Asked Questions About the Bobcat S590

Here are some common questions operators have about the Bobcat S590:

When did Bobcat go to Doosan engines?

Bobcat utilised Kubota engines for many of its machines until approximately 2015, at which point it transitioned to Tier IV Doosan motors. These newer Doosan engines often operate at higher temperatures and may consume more fuel compared to their predecessors, largely due to their emissions control systems.

What is the lifting capacity of a Bobcat S590?

The Bobcat S590 boasts a high lift path design, which enhances its load capacity and forward reach, even at full elevator height. Its rated operating capacity is 2,100 lbs (952 kg).

How much is a Bobcat skid steer?

The cost of a Bobcat skid steer, such as those in the 60-70 horsepower range with a cargo capacity under 2,200 lbs, can vary significantly. A brand-new Bobcat within this specification typically ranges between £45,000 and £60,000. For a good quality used or 'delayed version' medium-frame skid steer, you might expect to pay around £30,000, depending on age, hours, and condition.

Can you use any hydraulic oil in a Bobcat?

While you technically can use alternative hydraulic oils, Bobcat strongly recommends using its own brand of all-season hydraulic or hydrostatic fluid. These proprietary fluids are specifically formulated to ensure optimal performance, protection, and compatibility with Bobcat's sensitive hydraulic systems, helping to prevent issues and maintain warranty coverage.

Conclusion

The Bobcat S590 is an exceptionally capable and versatile skid steer loader, a true asset on any job site. By understanding its critical specifications, particularly the hydraulic system pressure, and by being aware of common operational issues—especially those related to the advanced fuel systems of its Doosan engines—you are well-equipped to keep your machine in prime condition. Most of the problems discussed, from lagging power to fuel injection concerns, can be effectively addressed with diligent troubleshooting and timely maintenance.

Regular checks of fluid levels, air filters, and fuel system components are not just good practice; they are essential for preventing costly downtime and ensuring the longevity of your investment. Should you encounter a problem that seems beyond your scope, or if you're unsure about any repair, do not hesitate to contact authorised Bobcat dealers or a professional service technician. Following these guidelines will help you maximise the performance and lifespan of your beloved Bobcat S590, ensuring it continues to deliver the robust performance you expect.

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