Site icon LEARN OIL ANALYSIS

Should my oil be this colour? Why hydraulic, turbine and compressor oils turn dark?

Oil colour change, oil color, oil darkening, oil turned brown, oil turned black

This article will answer the following questions.

Should I change my oil if it’s changed colour?

The answer is not necessarily. The first thing to establish is why it has changed colour. Lubricating oil is very suspectible to colour changes through oxidation and thermal degradation and it doesn’t take that much to cause a visual change. In fact colour changes are often some of the earliest signs of oil deterioration or localised overheating, but just because it’s darker doesn’t mean the oil is totally spent and it may still be in its prime of life. However there are other causes of colour changes such as contaminants and also evidence of air entrainment causing microdieseling that are cause for concern. This turns the oil as black as diesel engine oil. Furthermore, an oil can be perfectly crystal clear and light yet still not be serviceable so a colour change is important information, but should not be something to take a knee jerk reaction to.

The first action you should take is to take a lube oil sample, which compared to a costly oil change or an even costlier machine failure is well worth doing and has considerable cost savings.

The test suite should include ASTM D1500 colour or a close equivalent method to monitor the darkness of the sample. If this is not a one off and a regular analysis programme you can trend this data. Equally if your lab photographs samples then you can visually see the colour changes across samples over time.

What colour should my oil be?

The first thing to establish is there is no good or bad colour of an oil. Most oils start off light in colour, but naturally get darker over time with some doing so quicker than others. What is important to note is any rapid changes or changes that do not occur normally with this lubricant.

Causes of colour change.

The most common causes of a colour change include:

Remember: colour changes where the oil gets lighter are also significant too so it is not just darker. This can happen when the darker oxidised oil is being mixed with a lighter oil through e.g. seal leaks.

Measurement System for colour

To allow a standardised way of referring to the darkness of an oil your laboratory will implement something close to the ASTM D1500 Colour scale from 0 which is water white to very dark almost black 8. The actually colour needs to be ignored in this scenario as it could be a dyed lubricant and it’s the darkness that is important. So calling it a colour scale is really a misnomer and it should be called a darkness scale.

How to prevent and manage the causes of colour changes?

There are several ways to address causes of darkening oils related to the causes highlighted above. An oil analysis sample is a great way to begin this process of identifying the cause. Once identified you have the following options.

If you want to find out more about what to do about colour changes in your lubricants then click the contact us button at the bottom right of this screen to get in touch.

Exit mobile version