A practical guide to mixing hydraulic oil grades, the risks involved and when a full oil change is the safer option.
Mixing hydraulic oil grades such as ISO 32 and ISO 46 is a common question in plant, industrial and mobile hydraulic systems. While it may seem harmless, the reality depends on the system, operating conditions and how the oil is being used.
Understanding whether you can mix hydraulic oil grades helps prevent performance issues, contamination problems and unnecessary wear.
If you are unsure which oil your system should be using, try our
Hydraulic Oil Advisor tool
or read our guide on
Hydraulic Oil Grades Explained.
Some machines require specialist or OEM-specific hydraulic oil. Using the wrong oil can cause serious damage.
Check Your Oil NowMixing ISO 32 and ISO 46 creates a blended viscosity somewhere between the two, which may not match the system’s required specification.
When these two hydraulic oil grades are mixed, the resulting oil does not behave exactly like either grade.
To understand how viscosity affects performance, see our Hydraulic Oil Viscosity Chart.
There are situations where mixing ISO 32 and ISO 46 may be unavoidable:
In these cases, the goal is to maintain operation temporarily – not as a long-term solution.
Mixing oil grades can lead to issues, especially in demanding systems:
If the wrong oil grade is already causing problems, read: What Happens If You Use the Wrong Hydraulic Oil?.
Mixing oil is often confused with normal topping up — but they are not the same.
If a significant amount of the wrong oil has been added, a full oil change is usually the safest option.
ISO grades relate directly to oil thickness at operating temperature.
Mixing them removes that precision, which is why correct grade selection is important.
For a full comparison, see: ISO 32 vs 46 vs 68 Hydraulic Oil Explained.
To avoid issues caused by mixing hydraulic oil:
Regular maintenance also helps extend oil life. See: How Often Should You Change Hydraulic Oil?.
If you’ve mixed oil or need the correct grade urgently, we can help.
See our Emergency Hydraulic Oil Supply page for fast delivery and support.
Yes, but only in small amounts for temporary use. It is not recommended as a long-term solution.
The viscosity changes, which can affect performance, lubrication and system efficiency.
If a significant amount has been mixed, a full oil change is usually recommended.
It depends on the system and operating temperature. ISO 46 is commonly used for general applications.
