Hydraulic Oil Vs. Engine Oil: Can Engine Oil Safely Replace Hydraulic Fluid?

Understand the Key Differences & Risks to Protect Your Equipment and Avoid Costly Maintenance

Some companies, in an attempt to cut costs, opt for general-purpose products or common alternatives. Many experts have heard of the widespread practice of using engine oils with the lowest API grades, such as SAE 10, SAE 20, or SAE 30, as substitutes for hydraulic oils like ISO 32, ISO 46, or ISO 68.

Despite their similar appearance, engine oil and hydraulic oil are two products that are NOT interchangeable. They are manufactured with different base oils and additive formulations. This means they cannot be substituted for each other in use and can have negative consequences if used improperly. For instance, using engine oil in a hydraulic system can lead to reduced performance and severe wear, while using hydraulic oil in an engine can damage seals and other components.

It's undeniable that this practice can save some money in the short term! But the question is: Is it safe? Is it truly acceptable to use engine oil as a substitute for hydraulic oil?

What is Engine Oil?

Engine oil typically refers to a petroleum-based lubricant used to lubricate the moving parts of an engine. Its role is to help cool, clean, and prevent corrosion within the engine. Generally, engine oils have a much lower viscosity than hydraulic oils, meaning they flow more easily at lower temperatures, which is suitable for their lubricating role in an engine.

What is Hydraulic Oil?

Hydraulic oil, on the other hand, is a mineral-oil-based lubricant designed to keep hydraulic systems cool and running smoothly. It is specifically formulated for hydraulic applications, capable of withstanding extreme high temperatures and pressures while providing excellent wear protection.

Are Engine Oil and Hydraulic Oil the Same Product?

While both are lubricants, they are essentially two completely different products. Engine oil is specifically engineered for cleaning and protecting internal combustion engines, whereas hydraulic oil is a non-flammable fluid used in hydraulic systems. Although their functions might seem similar, they are not interchangeable.

Is It Safe to Substitute Engine Oil for Hydraulic Oil?

The short answer is: No, it is not safe. Engine oil and hydraulic oil should not be interchanged; they are fundamentally different.

While engine oil might seem like a "viable" alternative in the short term, prolonged use will lead to component wear, decreased performance, and even system damage. The core function of hydraulic oil is energy transfer, and engine oil is not designed for this. Substituting engine oil for hydraulic oil is a costly mistake.

Can Engine Oil Be Mixed with Hydraulic Oil?

Technically, mixing is possible, and some experts might say it's "usable." But the real question you should ask is: What happens next?

When engine oil is mixed with hydraulic oil, its viscosity will decrease, making it ineffective at lubricating moving parts. If you continue to use this mixed oil, sludge is likely to form on equipment surfaces. Soon after, you'll observe increased equipment vibration or other issues like corrosion and accelerated aging.

Why Is Engine Oil Unsuitable for Hydraulic Systems?

Engine oils are primarily designed for engine lubrication and cooling. While they can tolerate some pressure, they are not engineered for high-pressure hydraulic systems! The most common consequence is that engine oil quickly breaks down within a hydraulic system, leading to a significant drop in efficiency.

The end results are often one of two things:

• Rapid equipment damage due to inefficient lubrication.

• Soaring repair costs as you're forced to replace the oil or repair the system.

In some cases, it can even lead to serious accidents or asset loss.

Why Is Hydraulic Oil Unsuitable for Engines?

Hydraulic oil does not possess the necessary lubricating properties required for engine operation. If hydraulic oil is used in place of engine oil, it will lead to rapid corrosion.

More critically, hydraulic oils have a lower flash point, making them more susceptible to ignition within an engine, which can lead to fire. They are simply not designed for engine systems.

Conclusion

Hydraulic oil and engine oil each have their specific uses and should never be interchanged. Incorrect usage can lead to equipment damage, reduced performance, and even safety risks. To protect your equipment and save long-term costs, always choose the correct type and viscosity of lubricant.