Komatsu PC18MR‑3 Hydraulic Level Checking

[MikePhua]

Understanding the Machine
The Komatsu PC18MR‑3 is a compact mini‑excavator designed for maneuverability in tight job sites. It has a closed‑center hydraulic system powered by a variable‑displacement pump.  Maintenance of hydraulic fluid level is essential for system health and proper function.
Issue with Hydraulic Level Fluctuation
An operator reported that the hydraulic fluid level on their PC18MR‑3 appears to change overnight: when they park the machine with the boom at a 90° angle, the level read “middle.” But by the next morning, it sometimes reads nearly empty, and after use, the level may shift higher.  They were unsure what the correct boom position should be when checking, and whether the sight‑glass (“circle indicator”) should read middle or top.
Expert Guidance on Correct Level Check Position
A long‑time forum member advised that for Komatsu mini‑excavators, the proper procedure is to:

1. Extend the stick (arm) fully out.
   
2. Fully open the bucket.
   
3. Lower the boom so its weight rests on the ground.
   This configuration allows the hydraulic components to settle into a neutral state — giving the most accurate fluid‑level read.
   

Why the Level Changes
According to the forum discussion, the likely reason for the fluctuation is thermal expansion: hydraulic oil expands as it gets warm, and because this machine doesn’t have a very large reservoir, the difference between “cold” level and “warm” level can be quite significant.
Practical Checking Tips

• Always check fluid level when the machine is cool and on level ground, with the boom and arm in the correct “rest” position (stick out, bucket open, boom down).
  
• Use the sight‑glass / level indicator while the machine is off, to avoid pressure effects skewing the reading.
  
• Inspect for leaks: If the level is dropping overnight, verify that there is no hydraulic fluid leaking from hoses, connections, or seals.
  
• Maintain a maintenance log: note the level at each check, plus temperature or hours of operation; over time, patterns will emerge that can indicate a developing problem.
  

Why This Matters
Running with incorrect hydraulic fluid levels can lead to:

• Cavitation in the pump (if fluid is too low)
  
• Overfilling issues, putting pressure on the reservoir, or causing overflow
  
• Accelerated wear on hydraulic components due to inadequate oil volume or aeration
  

Conclusion
For the Komatsu PC18MR‑3, checking hydraulic fluid level requires careful positioning of the boom and arm, and must account for changes in fluid volume due to temperature. By following the correct level-check procedure and keeping an eye out for leaks or other issues, you can maintain hydraulic system health and avoid damage or operational problems.