How to know if you're using the right hydraulic oil?

June 26, 2025

Is Your Hydraulic System Thirsty for the RIGHT Oil?

Here's How to Tell!

Hydraulic systems are the unsung heroes behind countless operations, from heavy machinery to delicate manufacturing processes. But like any hero, they need the right fuel to perform at their best. And when it comes to hydraulics, that fuel is the correct hydraulic oil.

Using the wrong hydraulic oil can lead to multiple problems, ranging from decreased efficiency to catastrophic equipment failure. So, how do you know if you’re using the correct oil, or if it's struggling with a bad match? Let’s find out.

The Obvious First Step: Check the Manufacturer's Manual!

We know, we know – it sounds simple, but it's often not checked. Your equipment's manufacturer knows their machinery best. The operator's manual or service manual is the most reliable source for using the correct hydraulic oil and finding the correct specifications.

Look for:

Viscosity Grade (ISO VG): This is very important, and it will typically be a number like ISO VG 32, 46, or 68. This indicates the oil's resistance to flow at a given temperature.

Performance Specifications: The manual might also list specific industry standards (e.g., DIN 51524 Part 2 (HLP), ISO 11158 (HM), or manufacturer specifications). These codes ensure the oil has the right additives for anti-wear, rust protection, and oxidation stability.

If you don't have the manual, you can always call us with the make and model, and we can find this out for you.

Beyond the Manual: Signs Your Hydraulic Oil Might Be Wrong (or Worn Out)

Even with the right oil, conditions change. Here are some signs that your hydraulic oil might be incorrect, contaminated, or simply past its prime:

Sluggish Performance & Reduced Power:

What it looks like: Cylinders extending or retracting slowly, a lack of lifting power, or general weakness in hydraulic functions.

Why it happens: Oil that's too thin might not provide proper lubrication or sealing, leading to internal leakage. Oil that's too thick can cause excessive drag and make the pump work harder.

The tell: If your system feels "tired," the oil could be a culprit.

Excessive Heat Generation:

What it looks like: The hydraulic reservoir or lines feel unusually hot to the touch, or your system's temperature gauge is consistently high.

Why it happens: Incorrect viscosity leads to increased friction. Oil that's too thick generates more shear heat. Oil that's too thin might not dissipate heat effectively. Contaminated oil can also cause friction.

The tell: Overheating is a bad sign for your hydraulic system's health.

Unusual Noises (Whining, Grinding):

What it looks like: Your pump is whining loudly, or you hear grinding/chattering sounds from hydraulic parts.

Why it happens: This often indicates cavitation (vapour bubbles forming and collapsing in the oil) or inadequate lubrication. Wrong viscosity, air in the system, or low oil levels can cause this.

The tell: Your hydraulic system shouldn't sound like it's in pain!

Foaming or Milky Appearance:

What it looks like: The oil in your machine has a foamy top layer, or the oil itself looks cloudy or milky.

Why it happens: Foam indicates air contamination, which can be due to a low oil level, a leak in the suction line, or an oil with poor anti-foaming properties (i.e., the wrong type). A milky appearance strongly suggests water contamination.

The tell: Visible changes in the oil's appearance are a clear sign of trouble.

Frequent Seal Leaks or Hose Failures:

What it looks like: You're constantly replacing seals or hoses, and there's constant oil leakage.

Why it happens: The wrong type of oil can be incompatible with the sealing materials in your system, causing them to degrade, harden, or soften prematurely. Extreme temperatures from incorrect oil can also make this happen

The tell: Leaks are a messy and costly problem, and often point back to oil issues.

Discoloured or Burnt-Smelling Oil:

What it looks like: The oil is dark brown or black (should be amber/clear) and has a distinct burnt odour.

Why it happens: This shows severe oil degradation, often due to overheating and oxidation. The oil has lost its lubricating properties and is no longer protecting the machinery parts.

The tell: Change the oil immediately.

When in Doubt, Get a Sample Analysis!

For valuable machinery, the most accurate way to know the health and suitability of your hydraulic oil is to perform a professional oil analysis. We can help you out with this!

Viscosity: To confirm it's still within spec.
Contaminants: Water, dirt, wear metals (which indicate component breakdown).
Additive Levels: To see if the oil's protective properties are still active.
Oxidation & Nitration: Indicators of oil degradation.

The Takeaway

Choosing and maintaining the correct hydraulic oil isn't just about increasing your equipment's life; it's about optimising performance, preventing costly downtime, and ensuring safety. Always start with your manufacturer's recommendations, and keep an eye (and ear) out for the warning signs.

Need high-quality hydraulic oil that meets the toughest specifications?