Six Signs That Industrial Grinding Oil Might Need To Be Changed

Posted on: 10 May 2018

Over time, industrial grinding oils will age and wear out. Industrial grinding oils need to be changed before they become excessively degraded to ensure both safety and proper machinery operation.

You need to know what the symptoms of old and less effective oil are so that your grinding oils are promptly changed. The following are six signs to look out for that indicate that it's time to change your industrial grinding oil:


As metalworking fluids like grinding oils become older, their color will begin to change. A typical oil will be clear when new if it's synthetic. If the oil is semi-synthetic, it may be either transparent or slightly milky when new. A soluble oil will first appear milky white.

As oils age, they may start to look either black or gray. This is typically an indication that bacteria are proliferating in the oil. Alternatively, grinding oils may become yellowish or brownish over time if they have been contaminated by tramp oil. 

Grinding oils need to be replaced if they start to look black, brown, or yellow. 

Unusual odors

Grinding oils may eventually become rancid if microbes start to grow and multiply in them. Oils that are giving off an unusual smell should be changed. Also, something should be done within the machinery itself to prevent the spread of microbes in the oil.

Typically, a biocide can be used to prevent future problems with microbe growth after oil is changed. 

Contaminants floating in fluid

There shouldn't be any solid substances floating around in grinding oil. If there appear to be chips or small particles, these contaminants should be removed with a skimmer. If contaminants are repeatedly seen floating on oil, it's a good idea to inspect the oil filtration system and repair any irregularities. 

Foaming on the surface

Foaming on the surface of grinding oils doesn't necessarily indicate that the oil needs to be changed. It could be an indication that the oil is merely too highly concentrated so that water needs to be added.

Alternatively, foaming might indicate that flow rates are too fast or the oil has been contaminated by some type of chemical cleaner. 

Excessively low sump levels

It's important to check the sump level every day when machinery operation begins. Sump levels that are excessively low indicate that oil has been leaking away somewhere. Metalworking fluids need to be added at the right concentration to keep sump levels at a high enough level. 

Dirty machinery

If machinery is becoming dirty as it comes into contact with grinding oils, it's a good indication that the emulsion in the oil is becoming unstable. This is usually caused by faulty filters or fluid contaminants.