Oil Change Intervals and Fluid Sampling
A fixed hour-based oil change either wastes fluid life or replaces contaminated oil too late. Condition-based change is smarter: a regular fluid sample reveals cleanliness class, water content and additive depletion. This guide explains how to draw samples correctly, read the results and set the change date from data.
View hydraulics basicsWhy change by condition instead of a fixed interval?
A change based on a fixed hour count ignores the real load. A clean system with good filtration often lasts twice the catalogue life, while a dusty or humid environment ages the oil sooner. The condition-based approach measures instead of guessing: cleanliness, water and additive reserve set the date, not the calendar.
- Fresh oil is rarely clean enough - new drums often sit at ISO 21/19/16 and need filtering before use.
- Over 70 % of hydraulic failures trace back to contaminated or degraded oil.
- Water and particles act together: moisture drives corrosion and speeds up additive depletion.
How do I take a meaningful fluid sample?
The most common error is a dirty sample: draw it carelessly and the lab measures the bottle, not the oil. Take the sample with the system warm and running, from a fixed sampling point, never from the tank bottom or the drain valve. That keeps the sample representative and comparable over time.
Which values decide the change?
Three metrics carry the decision: the cleanliness class per ISO 4406, the water content, and the state of the additives together with viscosity. Cleanliness and water can often be checked on site, while additive depletion and oxidation come from the lab. Only when values run out of the target band for good and filtration no longer helps is a change due.
Three numbers for particles at 4, 6 and 14 microns - the lower, the cleaner.
Understand cleanlinessFree water clouds the oil and drives rust, dissolved water weakens additives.
View the basicsFrequently asked questions
How often should I take a fluid sample?
For stationary systems every 2000 operating hours or twice a year is common, and more often for critical or mobile equipment. What matters more than the exact spacing is a fixed, steady rhythm so a meaningful trend can build over time.
At what water content does it get critical?
As a guide, 200 to 500 ppm, that is 0.02 to 0.05 percent, is the concern zone. Visible cloudiness points to free water and clearly excessive levels. Free water drives corrosion and additive depletion and should be removed promptly.
Can I just filter the oil instead of changing it?
Particles can be filtered out to restore the cleanliness class. But if additives are depleted, viscosity has shifted or the oil has oxidised, only a change helps - filtration cannot restore aged oil.
Plan oil changes from data
Our hydraulics specialists help with sampling, limit values and the right filter concept for your system.
Condition-based
Change by measured values, not a fixed calendar.
Cleanliness in focus
ISO 4406 and water content clearly explained.
Clean sampling
Representative samples for reliable trends.
Expert advice
Hydraulics specialists read the lab report with you.