Follow the machine's specified interval as a baseline, then let oil sampling override it in both directions. Change the oil after any major component failure regardless of hours, and expect to change it more than once: the first change removes the bulk of the debris, and a short follow-up interval catches what the filter released afterward.
What triggers a change
| Trigger | Action |
|---|---|
| Specified service hours reached | Change to schedule. This is the baseline, not the whole story. |
| Oil analysis shows contamination or additive depletion | Change now, regardless of hours. Analysis overrides the schedule. |
| Oil is dark, burnt-smelling or contains visible particles | Change and investigate the cause, not just the oil. |
| Any pump, motor or cylinder failure | Change, flush and change again at a short interval. Treat the whole circuit as contaminated. |
| Water or coolant contamination | Change, correct the entry point, change again to remove residual moisture. |
| Machine works in high heat or heavy dust | Shorten the interval. Cooling and filtration both work harder in these conditions. |
| Machine sits unused for long periods | Change before returning to service. Condensation accumulates in stationary tanks. |
How to confirm it
- Operate the machine to warm the oil before draining
Warm oil carries suspended contaminants out of the system and drains more completely. Draining a cold machine leaves a significant proportion of the old oil and its contamination behind, which is one of the reasons a change sometimes appears to make no difference.
- Clean the area around the drain and fill points
The dirt around the fill point goes straight into the system the moment it is opened. On a dusty site, cleaning first is not a formality — it is the difference between a service and a contamination event.
- Drain completely, including low points
Open the drain and allow the tank to empty fully. Where the system has separate drain points on lines and components, use them. Oil sitting in a low line is old oil that will mix with the new.
- Service the suction strainer as well as the return filter
This is the step most often skipped and one of the most consequential. A clean return filter with a blocked suction strainer starves the pump, which is exactly the failure the oil change was meant to prevent.
- Replace or clean the breather
A blocked breather pressurizes or evacuates the tank as oil volume changes and draws contaminated air in through seals instead. Breathers are inexpensive and frequently ignored.
- Refill with the specified oil to the correct level
Use the correct viscosity grade and specification for the machine and the climate. Measure the level by the specified method, on level ground, rather than estimating by the sight glass while the machine is working.
- Run the machine and re-check level
Operate the functions through a full cycle to fill lines and cylinders, then re-check the level and top up if needed. A system that appears full before circulation can be meaningfully low afterward.
- Re-check for leaks and record the change
Check the drain plug, filter housings and any disturbed fittings. Record the hours and the oil used, so the next change can be assessed against actual conditions rather than against an assumption.
What to do about it
After a failure, change the oil at least twice: an initial change with a new filter, then a short interval — typically tens of hours rather than hundreds — with another filter. The second change is what removes what the first one released, and skipping it is how a new pump fails within weeks.
If oil analysis reports elevated wear metals but no component has failed, shorten the interval and investigate. Metals in the oil mean something is wearing, and identifying it before it fails is the entire purpose of sampling.
If the oil consistently darkens faster than the interval suggests it should, look for continuous bypass and for breathing contamination. Both degrade oil faster than hours alone, and neither is visible on a service sheet.
Keep a record of oil used, hours at change and analysis results on every machine. This is what converts maintenance from a schedule you follow into a decision you make, and it is what allows a repair to be planned instead of absorbed.
Need the parts this covers?
Send the machine model, serial number and the part numbers you need. We confirm fitment before payment and state the grade of every line — genuine, OEM-quality or aftermarket.
Request a quoteFrequently asked
Can I extend the interval if the oil still looks clean?
With sampling, yes, and this is a legitimate saving. Without sampling, no — appearance tells you about suspended contamination but not about additive depletion, water content or viscosity breakdown, which are the properties that protect components.
Do I need to flush the system after a pump failure?
You need to remove the debris, which can be done with staged oil and filter changes rather than a dedicated flushing procedure. Either approach works if it is done thoroughly; what does not work is one change and back to work.
How much oil does an excavator hydraulic system hold?
It varies enormously with machine size, from tens of liters on a compact machine to several hundred on a large one. Use the specification for your machine — and note that the system holds more than the tank, which is why partial draining leaves old oil behind.