Technical Help: How Often Should Machine Coolant Be Checked?

Checking your machine coolant is an often overlooked aspect of metalworking that can have disastrous effects on your machine and reduce its lifespan. Despite this, many metalworkers are unsure about how often these checks should be performed, and what they should cover.  

So, how often should machine coolant be checked? In order to comply with HSE MW05 as a metalworking fluid user, your machine coolant should be checked weekly. These checks should include inspecting the coolant for tramp oil or contamination, dipslide testing for bacteria, and pH testing to check it’s within the recommended dilution range.

Keep reading to find out more about how frequently to check your machine coolant, how to perform the checks, and what the benefits of changing your machine coolant are. 

How Frequently Should Machine Coolant Be Checked? 

Any metalworking fluid is required to be checked weekly. If coolant is well maintained and operating as it should then monthly testing may suffice. Weekly testing is needed if there are problems with coolant that need to be sorted out quickly because of the potential risk to health. Ideally, visual inspections should be completed by operatives whenever a machine is in use.

Visual Inspections:

Tramp Oil – Tramp oil is a substance which contaminates machine coolants. It produces a layer across the coolant within the sump and can lead to increased bacterial growth within the coolant. This can cause problems both with coolant and machine performance, as well as posing risks to an operator’s health. 

A visual inspection of the machine sump can determine whether tramp oil is a problem. If tramp oil is present it can be removed by installing a tramp oil skimmer, which will gradually remove the film. A coolant recycling machine, such as a Freddy can also filter out contaminants and refill the machine with the filtered coolant.

To see a tramp oil skimmer in use, watch our pH Testing, Dilution Testing & Dipslide Testing video which shows a variety of testing methods in action.

Monthly Coolant Checks should include:

Dipslide Testing – HSE guidelines advise conducting regular dipslide testing to check for bacterial and fungal contamination which may be present in the coolant. Dipslides should be incubated at a temperature of 30 degrees for 48 hours to check for bacteria and then for a further 24 hours to check for any fungal contamination. 

The below image supplied by the UKLA, shows dipslides in the upper panel from left to right, with an increasing number of bacterial colony-forming units. In the lower panel the yeast (left) and fungi colonies (right) are recorded as light, moderate and heavy contamination. It is important to note that the colour of dipslide and colonies may vary depending on the kit used to conduct the tests.

dipslide test images


Dilution Testing – To ensure your coolant is performing correctly, it’s vital the coolant is used within the manufacturers recommended dilution range. This information should be available on the coolant’s technical data sheet. To check the dilution of your coolant, use an easy to use hand refractometer.

pH Testing –  The pH of your coolant should be maintained within the manufacturer’s recommended range. If the pH of your coolant drops below this recommended operating range, corrosion and microbial growth can occur. If the pH of the coolant increases too much there is an increased risk of skin irritation to operatives. 

It is important to note that COSHH requires that all coolant checks should be recorded regularly and results should be retained for at least 5 years. 

More detailed information on the coolant tests required by law can be found in the UKLA’s guide to the Safe Handling and Disposal of Metalworking Fluids.

How Long Does Machine Coolant Last?

Machine coolant that is well maintained with routine testing can last many months, even years. Filtration systems such as a Freddy Coolant Vacuum can prolong the life of machine coolants by filtering out swarf, chips, and tramp oil before pumping back into a clean machine sump. Coolant recycling is a great way to prolong the life of the coolant and make sure that it is free of debris that can reduce the effectiveness of the coolant. It’s also better for the environment! 

What are the Benefits of Coolant Monitoring?

There are many benefits to coolant monitoring. Not only does it enable the machine to do its job effectively, there will then be minimal health risks to operatives. As well as these onsite benefits, should you receive a visit from the HSE, you will be able to provide historical reporting that details the tests conducted, results from those tests and any remedial actions taken to solve problems with your coolant. This makes you compliant with HSE MW05. 

Here is a summary of the benefits, along with an explanation on how this will help improve both the condition of your coolant, but the working environment too.


Benefit Explanation
Compliant with HSE MW05 By routinely checking & testing your coolant and keeping historical records of results, you are meeting the HSE’s requirements as a metalworking fluid user
No risk to operatives When you monitor your coolant you reduce the health risk to operatives – avoiding respiratory problems including lung disease, as well as skin diseases such as Dermatitis.
Increased sump life By performing regular routine coolant checks such as Dilution checks, pH testing, Dipslide Testing & filtering coolant you will prolong the life of your metalworking fluid.
Increased Tool Life If your coolant is free of contaminants, is in the correct dilution range and there are no potential bacterial problems your coolant can do its job without causing unnecessary wear and tear on tooling.
No machine down-time If you look after your coolant you reduce the risk of having to stop production for machine cleans or coolant changes, meaning there are no delays to production.

What Happens if You Never Change Your Machine Coolant?

If you never change your machine coolant and are not maintaining it correctly with routine coolant monitoring then it will stop doing its job. Your machine will not be protected against wear and tear when machining. The coolant will not be cooling down all of the necessary parts of the machine in order for it to work effectively. It also poses an extreme risk to the health of operatives.

Tool life will shorten and result in the need to replace tools more often,  increasing costs. This will result in a build up of bacteria, fungi, tramp oil, and your dilution rate will not be within the manufacturers guidance, meaning the coolant may not be doing its job at all. 

Machine Coolant at Pennine Lubricants

At Pennine Lubricants, we blend and manufacture a wide range of machine coolants for the metalworking industry at our manufacturing plant in Sheffield. Our technical team works with customers to ensure they are using the right machine coolant for their application. We are here to help advise on the correct coolant for your application, and can come and visit you on site to understand your requirements and make suggestions to help rationalise the number of products in use on site. 

We also offer a full fluid management service, where a technical engineer can visit you onsite to complete the required coolant checks, give help and advice, troubleshoot any application problems and help resolve any changes to coolant quality.  

If you’d like more information on how we can help you find the correct coolant for your application, or would like help with routine coolant monitoring then get in touch with us today! 

Pennine are more than just a supplier, they offer technical support and expertise. They provide full regular monitoring of metal working fluids and any aspects that support the safe use and operation of the oils and coolants we use on our site. Kevin Martin, Health & Safety Manager, Abbey Forged Products

They offer an excellent service, are polite and offer helpful advice. Mathew Kelly, Operations Manager, Barrett Steel

The communication from Pennine is great, we are always fully informed of our order status and they always deliver on time. I have been really impressed with the quality of their oil. Mark Wood, Fitter, Betney Cop Restoration Co.

We've recently changed to Pennine Lubricants, I can't thank Bob enough for the effort and service that's provided every time we order. Always happy to do business. Mylo Charlesworth, Purchasing and Warehouse Operative, CNC

In fifteen years of dealing with Pennine Lubricants, I have found the service to be impeccable. Jeremy Gosling, Director, Fine Grinding LTD

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