Cat 252B Skid Steer Hydraulic Oil Compatibility and Stalling Problem

[MikePhua]

Background on the Cat 252B
The Caterpillar 252B is a compact skid steer loader that features a hydraulic system with a pump delivering ~22 gal/min (about 81 L/min) at a relief pressure of ~3,335 psi.  Its hydraulic reservoir capacity is about 9.2 gal (35 L), with a total system capacity around 14 gal (53 L).  This loader is a widely used model in construction and maintenance because of its relatively light frame and solid hydraulic performance.

Oil Compatibility Question
One owner of a 252B (serial 252BTSCP02842) asked whether he must use Cat-branded hydraulic fluid or if generic hydraulic oils from retail stores (like AutoZone or Tractor Supply) would suffice. A highly experienced forum member responded that:

• You do not have to stick with Cat-branded oil.
  
• However, he strongly cautioned against using “anything with ‘Universal’, ‘Farm’, or ‘Tractor’” in the name, implying that many lower‑grade or low‑spec oils are not suitable.
  
• He recommended ISO AW 32 or SAE 10W hydraulic oil from a reputable major oil company.
  
• According to him, these viscosity grades work fine for the 252B’s system.
  

From a technical standpoint, ISO AW 32 is a common choice in many mobile hydraulic systems for moderate climates. The Cat maintenance documents (SEBU6250-21) also provide guidance on acceptable oil viscosities for skid steer hydraulics depending on ambient temperature.

Stalling Symptoms and Possible Causes
The same owner also reported that his 252B sometimes stalls: his RPM unexpectedly drops, especially when operating a breaker (hydraulic attachment), and occasionally the machine shuts off.
He wondered if:

• Low hydraulic fluid level could cause the stalling.
  
• There might be a low‑fluid “cut‑off” switch in the hydraulic system.
  

The forum advice was clear: no, there is likely no automatic shutoff switch linked to low hydraulic fluid.  The experienced user stated that in his opinion, low hydraulic level does not cut power to the engine.

Likely Technical Explanations
Based on the discussion and common skid steer behavior, possible causes for the stalling include:

1. Hydraulic Demand Overload
   • The breaker attachment draws a large volume of hydraulic flow. If the system cannot maintain sufficient pressure or flow (due to pump wear, fluid issues, or internal leakage), the engine may bog down under load.
     
2. Air or Contamination in Hydraulic System
   • Poor-quality oil, improper fill, or contamination (water, dirt) can reduce hydraulic efficiency.
     
   • Aerated (foamed) hydraulic fluid can cause cavitation, leading to erratic pressure and potentially stressing the engine when the hydraulics draw.
     
3. Engine‑Fuel or Injection Issues
   • While not directly discussed in the thread, stalling under high hydraulic load may also relate to fuel delivery, engine injection timing, or governor response.
     
4. Hydraulic Pump Wear or Internal Leakage
   • Over time, hydraulic pumps may develop internal leakage or wear that reduces their capacity to maintain system pressure under heavy loads, particularly when attachments demand high flow.
     

Recommended Troubleshooting and Solutions
To resolve or mitigate the problem, the following steps are advised:

• Verify and stabilize hydraulic fluid
  • Drain and refill with a high-quality hydraulic oil that matches Cat’s spec (or a major brand equivalent, e.g. ISO AW 32).
    
  • Make sure the fill is correct (not over or under) and take care during refills to avoid introducing air.
    
• Check hydraulic fluid condition
  • Sample the fluid to check for contamination (dirt, water).
    
  • If fluid is dirty, perform a flush or multiple partial changes, replacing the hydraulic filter afterward.
    
• Inspect the pump and hydraulic circuit
  • Monitor hydraulic pressures during operation (especially under attachment use) to see if the pump is maintaining correct pressure.
    
  • If pressures drop or fluctuate, consider pump evaluation or rebuild.
    
• Evaluate engine-demand behavior
  • Observe if the stalling happens only with the breaker or other high-flow implement.
    
  • Test with a different attachment or fewer hydraulic demands to isolate whether it’s a load‑specific issue.
    
• Use the proper Operation & Maintenance (O&M) Manual
  • The responsible forum user recommended obtaining the correct O&M manual (for his unit, SEBU7731) to understand Cat’s fluid specs, refill capacities, and maintenance intervals.
    
  • The manual can also help confirm safe operating limits, system relief settings, and service intervals.
    

Real‑World Cautionary Note
This issue is fairly common in older skid steers: operators sometimes downplay hydraulic system maintenance, especially when using non‑OEM fluids. But when high‑demand attachments like breakers or augers are installed, any weakness in the hydraulic system becomes amplified, often resulting in stalling or poor performance.
One small contractor reported that after switching from a generic “tractor hydraulic oil” to a premium ISO AW 32 oil and performing a full fluid change, his skid steer ran smoother and no longer stalled under heavy hydraulic load.

Conclusion

• The Cat 252B does not require proprietary Cat-branded oil; a high-quality ISO AW 32 or SAE 10W hydraulic oil from a major brand is acceptable and recommended by experienced users.
  
• Using lower‑grade “universal” or “tractor” hydraulic oils is discouraged because they may lack the necessary performance and contamination resistance.
  
• The stalling issue when using a hydraulic breaker is more likely related to hydraulic overload, fluid condition, or pump capacity rather than a low‑oil shutoff sensor.
  
• Proper diagnosis should include fluid sampling, pressure testing, and possibly hydraulic system servicing.
  
• Acquiring and referencing the correct O&M manual is an important step in verifying specifications, refill volumes, and maintenance procedures.
  

By following these steps, an owner can improve reliability, prevent future stalling, and extend the life of the 252B’s hydraulic system.