Should I Use AW32 or AW46 Hydraulic Fluid?

The higher the number associated with an oil or hydraulic fluid, the higher its viscosity is. This means AW46 is thicker than AW32 and will not flow as easily through a system (AW stands for anti-wear). AW68 hydraulic fluid has an even higher viscosity, so it will flow even slower.

The type of hydraulic fluid you need depends on several factors, including the operating environment and the specific requirements of your equipment.


AW32 is a mineral-based hydraulic oil specifically designed for machinery that operates in temperatures between −18°C and 49°C (−0.4°F and 120°F). It offers excellent anti-wear protection.


AW46 is another mineral-based hydraulic fluid designed for medium-duty service in temperatures between −22°C and 107°C (−7.6°F and 225°F). It offers excellent wear protection and oxidation stability as well as good air-release properties.


Finally, AW68 is a mineral-based hydraulic oil specifically designed for heavy-duty service in temperatures between −45°C and 135°C (−49°F and 275°F). It offers excellent wear protection, oxidation stability, air-release properties, and low-temperature performance.

The right hydraulic fluid can make a big difference in the performance and longevity of your machinery. It’s also important to take into account if your machinery is operating in the cold temperatures that can be common in the Upper Midwest.

AW32 will flow “better” in colder weather than AW46. For instance, if your machine’s space is unheated, you may want to consider AW32 instead of AW46. Also, don’t use fluids that are too “thin” for your hydraulic system. Something like transmission fluid (5/10W) may weep around the cylinder seals or degrade the pump seals over time.

Selecting the Right Fluid

Some of the most common uses for AW32 are in the agricultural and industrial sectors, while AW46 is more commonly used in construction and forestry. Finally, AW68 is often used in high-temperature applications, such as foundries, power plants, and steel mills, and for heavy equipment.

It is always important to consult your operator’s manual or a qualified technician before selecting your hydraulic fluid. If you have questions, Keller-Heartt’s experts would be happy to talk through your options with you.


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