6 Easy Steps to Ensure your Coolant Stays in Tip-Top Condition

If you’re shutting down for a period of time then there are a few things you can put in place now to ensure you can get your machines straight back up and running after the celebrations…

1: Skim any tramp oil from the surface of your coolant

Tramp oil is one of the most common and damaging contaminants found in CNC coolant systems, and removing it regularly is essential to maintaining coolant performance. When oil from hydraulics or slideways floats on the surface, it creates a barrier that prevents oxygen from entering the coolant. This encourages anaerobic bacterial growth, which leads to unpleasant odours, reduced coolant life, and a decline in machining performance. By skimming tramp oil regularly, you help the coolant “breathe,” stabilise its condition, and significantly extend sump life while keeping your machines running more efficiently.

Key actions to control tramp oil:

• Skim tramp oil from the coolant surface daily where possible with a Freddy Vacuum
• Use oil skimmers or separation devices for continuous removal
• Check machines for leaks (hydraulic or way oil) that may be contributing
• Avoid agitation that mixes tramp oil back into the coolant
• Maintain good housekeeping around machine sumps to reduce contamination ingress

2: Remove any solid contaminants from your coolant

Solid contaminants like swarf, fines and metal turnings are one of the fastest ways to degrade coolant performance if they are left to circulate or settle in the sump. These particles increase wear on pumps and tooling, disrupt coolant flow and create pockets where bacteria can thrive. Over time, they also form sludge at the bottom of the tank, reducing coolant capacity and heat transfer efficiency. Removing solids regularly helps maintain stable coolant condition, improves machining consistency and reduces the risk of machine downtime caused by blocked filters or damaged components.

Why removing swarf and solids is important:

• Prevents abrasive wear on pumps, seals, and machine components
• Improves coolant flow and heat dissipation during machining
• Reduces sludge build-up in the machine sump
• Limits bacterial growth sites within trapped debris
• Helps maintain consistent machining performance and surface finish

Best practices for effective removal:

• Regularly clean machine sumps and chip trays
• Use filtration systems such as conveyors, magnetic separators, or paper band filters
• Avoid allowing swarf to accumulate overnight or over weekends
• Ensure coolant return lines are not blocked by debris
• Schedule periodic deep cleaning of tanks, not just surface maintenance

3: Restore the level of your coolant to more than 75% of the sump volume.

Maintaining an adequate coolant level is often overlooked, but it plays a critical role in system stability and coolant life. When coolant levels drop too low, the fluid becomes more exposed to air, heat fluctuations, and contamination from chips and tramp oil. This increases the risk of bacterial growth and causes the coolant to degrade. Keeping the sump consistently above 75% capacity helps maintain thermal stability, ensures proper pump performance, and reduces the concentration swings that occur when top-ups are made too infrequently or in large volumes.

Why maintaining over 75% sump volume matters:

• Improves coolant temperature stability during machining cycles
• Reduces aeration, which helps limit bacterial growth
• Prevents pump cavitation and inconsistent coolant delivery
• Minimises concentration fluctuations from evaporation or carry-out
• Helps maintain consistent lubrication and corrosion protection

Best practices for coolant level control:

• Check sump levels daily as part of routine machine inspection
• Top up gradually using correctly mixed coolant, not neat concentrate
• Avoid letting levels drop below critical pump intake thresholds
• Monitor for unexpected losses, which may indicate leaks or excessive carry-out
• Link level checks with concentration testing to maintain balance across the system

4: Check dilution levels on each machine, make sure they are at the upper end of the recommended scale.

Coolant concentration is one of the most important factors in maintaining stability, performance, and tool protection. Running at the lower end of the recommended dilution range can leave the system under-protected, increasing the risk of corrosion, bacterial growth, and poor lubrication. Keeping concentration toward the upper end (within manufacturer guidelines) provides a stronger safety margin, helping the coolant resist contamination and last longer between maintenance interventions.

Why higher-end dilution control is beneficial:

• Improves resistance to bacterial growth and contamination
• Enhances lubrication, extending tool life and improving surface finish
• Provides better corrosion protection for machines and components
• Reduces risk of concentration drift caused by evaporation or carry-out
• Helps stabilise coolant performance across different machines

Best practices:

• Test each machine individually rather than assuming system-wide consistency
• Use a refractometer regularly to verify true concentration levels
• Adjust gradually using pre-mixed coolant rather than neat concentrate
• Record readings to identify machines that consistently drift out of range in PROCARE Fluid Cloud
• Ensure operator training includes correct mixing and topping-up procedures

5: Check the pH level of your coolant – if below 8.6 apply 0.2% of biocide.

pH level is a key indicator of coolant health and microbial stability. As coolant degrades, pH typically drops due to bacterial activity and contamination. When pH falls below 8.6, it signals that the fluid is becoming biologically unstable and more susceptible to rapid deterioration. In these cases, controlled biocide dosing can help restore balance and prevent further bacterial growth, protecting both coolant life and operator safety.

Why pH control is critical:

• Indicates early stages of bacterial contamination
• Helps maintain coolant stability and extend sump life
• Supports corrosion protection on machine surfaces
• Prevents unpleasant odours and skin irritation issues
• Ensures coolant remains within a safe operating condition

Best practices for managing pH:

• Test pH regularly as part of routine coolant checks
• Investigate sudden drops in pH (often linked to tramp oil or contamination)
• Apply biocide at a controlled 0.2% dosage when pH falls below 8.6
• Avoid overuse of biocide, as excessive dosing can affect coolant performance
• Combine pH monitoring with concentration and visual inspections for a full condition picture

6: Increase machine usage before shutdown periods to oxygenate coolant

Coolant health is strongly influenced by circulation and oxygenation. When machines sit idle for extended periods, especially over weekends or shutdowns, the coolant becomes stagnant. This creates ideal conditions for anaerobic bacteria to grow, particularly if tramp oil or contamination is already present. Running machines more frequently before downtime helps circulate the coolant, improve oxygen levels, and reduce the likelihood of bacterial build-up while the system is static.

Why oxygenation matters:

• Reduces anaerobic bacterial growth during idle periods
• Keeps coolant circulating and evenly mixed
• Helps prevent foul odours developing over shutdowns
• Improves overall fluid stability and consistency
• Supports better performance when machines restart

Best practices before shutdown periods:

• Run machines periodically before weekend or holiday closures
• Ensure coolant is fully circulated through all lines and sumps
• Avoid leaving stagnant pockets of coolant in isolated systems
• Combine with tramp oil removal and filtration before shutdown
• Restart with a quick coolant check (smell, concentration and appearance)

By following these 6 simple steps, you’ll give your coolant the best possible chance of staying clean, stable, and productive, so when you reopen, your machines are ready to perform straight away. Better coolant control means improved tool life, and more consistent machining results across the board.

We’re Here to Help You Keep Things Running Smoothly

If you’d like a second opinion on your coolant condition or need help with a particular application, our technical team is here to help. We work with manufacturers every day to diagnose issues, improve fluid life, and reduce downtime, and our advice is always free!

To find out more about our range of lubricants or our PROCARE Fluid Management service, get in touch with us today. We can help you move from reactive coolant maintenance to a more controlled, data-led approach that keeps your machines running at their best.

📞 Call us: 0114 285 2987
📧 Email: [email protected]