Hydraulic systems power the heavy lifting on excavators, loaders, cranes and most mobile plant. When they fail, the machine stops. Regular servicing catches fluid degradation, filter blockages and hose wear before they cause unplanned downtime or costly component damage.
This guide covers the complete hydraulic service procedure, from lockout/tagout through to pressure testing. It applies to most mobile and fixed hydraulic systems, but always cross-reference your OEM service manual for machine-specific intervals and specifications.
Before you start
Gather your tools: filter wrench, clean rags, fluid sample bottles, a calibrated pressure gauge and the correct hydraulic fluid for your machine. Check the OEM manual for the fluid specification (e.g. ISO VG 46 or CAT HYDO Advanced 10) and the filter part numbers.
If your team uses a maintenance checklist, pull it up before you start. Having the checklist in hand ensures you do not miss a step, especially on machines with multiple filter locations or complex hose routing.
Step-by-step service procedure
1. Prepare the machine and lock out
Shut down the engine and allow the hydraulic system to cool. Engage lockout/tagout procedures to isolate all energy sources. Cycle the hydraulic controls with the engine off to relieve residual pressure in accumulators, cylinders and lines. Hydraulic fluid under pressure can penetrate skin, so never loosen a fitting on a pressurised system.
2. Check fluid level and condition
Locate the sight glass or dipstick on the hydraulic reservoir. The fluid level should sit within the OEM-specified range. Draw a sample into a clean bottle before draining or filtering, as this provides a baseline for oil analysis.
- Amber/clear = healthy fluid
- Dark brown/black = heat-degraded, schedule a change
- Milky/cloudy = water contamination, investigate seals and breathers
- Metallic particles = internal component wear, escalate immediately
3. Replace the hydraulic filter
Remove the return-line and pressure-line filters using a filter wrench. Inspect the old filter element for excessive debris or metal particles. Install new filters of the correct OEM specification. Pre-fill spin-on filters with clean hydraulic oil before fitting to reduce air ingress on start-up.
4. Inspect hoses, fittings and cylinders
Walk around the machine and visually inspect every hydraulic hose. You are looking for:
- Cracking, abrasion or UV damage on the outer cover
- Bulging (internal reinforcement failure)
- Oil weeping at crimp fittings or swivel joints
- Cylinder rod scoring or seal leakage
Replace any hose that shows external damage. A burst hose under pressure is a serious safety hazard.
5. Bleed air from the system
With new filters installed and the reservoir topped up, start the engine at low idle. Slowly cycle each hydraulic function through its full range several times. Air trapped in the system causes spongy operation and can cavitate the pump. Monitor the reservoir level and top up as needed.
6. Test pressures and record the service
Connect a calibrated pressure gauge to the test port. Run the system to operating temperature and compare readings against OEM specifications. Record all pressures, filter part numbers, fluid volume added and any defects in your equipment maintenance log.
Common faults and actions
| Fault | Possible cause | Action |
|---|---|---|
| Slow cylinder movement | Low fluid, blocked filter or internal leak | Check level, replace filter, test pressures |
| Excessive pump noise | Cavitation from air ingress or low fluid | Bleed system, check suction line and fittings |
| Overheating | Blocked cooler, degraded fluid or relief valve fault | Clean cooler, sample fluid, test relief valve |
| Oil leaking at cylinder rod | Worn rod seal | Replace seal kit, inspect rod for scoring |
| Foaming in reservoir | Air leak on suction side or water contamination | Tighten suction fittings, check breather cap |
Fluid analysis and contamination
Sending fluid samples to a laboratory for analysis is the most reliable way to track hydraulic system health. A standard analysis report covers particle count, water content, viscosity and metal wear elements. Many labs provide trending over multiple samples so you can spot degradation before it causes a failure.
Under AS 4024 (machine safety) and general WHS obligations, employers must ensure hydraulic systems are maintained in a safe condition. Fluid analysis provides documented evidence of proactive maintenance, which is valuable during audits and incident investigations.
Service intervals
| Task | Typical interval | Reference |
|---|---|---|
| Fluid level check | Daily (pre-start) | OEM manual |
| Fluid sample for analysis | Every 250-500 hours | Oil analysis provider |
| Filter replacement | Every 250-500 hours | OEM manual |
| Hose and fitting inspection | Every 500 hours or weekly | OEM manual / AS 4024 |
| Full oil change | Every 2,000-5,000 hours | OEM manual / oil analysis |
Download a preventive maintenance schedule template to map these intervals against your fleet.
Going digital with MapTrack
Paper-based service records are easy to lose and hard to trend. With MapTrack, you can attach a QR code to each machine and scan it to launch the hydraulic service form on your phone or tablet. The system captures the timestamp, technician name, fluid volumes and pressure readings automatically.
Overdue services trigger automated alerts, and all records are stored centrally so your maintenance team can review service history, track fluid analysis trends and produce compliance reports without chasing paper.
