How to Maintain your Metalworking Coolant

How to Maintain your Metalworking Coolant

Coolant Maintenance in many applications is crucial to tool-life, how your tool cuts, and most importantly your bottom-line. The basic idea behind maintaing your coolant is somewhat similar to maintaining crystal clear water in a pool.

Of course, just as it can be nearly impossible to keep your pool perfect all season long, it can be difficult to keep your coolant at peak performance.


How to Maintain your Metalworking Coolant

Makeup Concentration

When you clear your sump and start over with brand new coolant, this initial coolant mixture is often times referred to as a “Makeup” Concertation. It is a simple recipe, if you will, that tells you precisely how to make your Coolant.

Water Concentrations in Coolants

When using a water in your coolant, it must be understood that this will be one of the first components to your Coolant that will disappear. Water is lost not only from it getting carried away on metal chips and parts, but it has additional loss through evaporation.

Refractometer Factor

The refractometer factor is used in determining concentration of a metalworking fluid. Each chemical concentrate product has a refractive index factor for determining concentration. Always use Data and Information Sheets for that products specific refractive index factors. Multiply the refractive index (refractometer reading) by the refractometer factor and the result is the concentration of the working solution in percent. (The factor for most emulsion fluids is 1.0 so that the BRIX refractometer reading is the fluid concentration.)

Cole-Parmer RSA-BR82T Refractometer 45 - 82%, Brix from Cole-Parmer

prism in a refractometer
Viewing through a Refractometer

The Smells of Coolant

You come into work, setup your machine and get to work. You start smelling what is often times is described as a rotten egg smell. Why?

What caused the smell can sometimes be a mystery. It could be something as crazy as the machine operator spitting is pistachio shells into the sump (real-story), or it could simply be a miscalculation in current maintenance standards. Whatever the cause may be, the effect is bacteria growth within your coolant. this bacteria will begin to eat away at your fluid and excrete sulfur. This is where the rotten egg smell comes from.

Once you have bacteria running through your coolant, they will quickly alter the coolant. your coolants ability to lubricate and provide corrosion protection will rapidly decline. Aside from excreting sulfur, they also excrete corrosive acids and salts that will lead to lowered pH and if left untreated will start corroding everything it touches.

Minimizing Bacteria Growth

To keep bacteria growth to a minimum follow the 5 C’s

  1. Coolant Concentration – Always maintain a proper coolant concentration.
  2. Clean Machine – If it doesn’t go into a machine, it should not be in or near the machine. Getting food or beverages in your coolant for example would be the easiest way to get a bacterial growth spike.
  3. Contamination Free – Similar to 2, however this extends to anything. Do not put anything into your coolant that is not part of it’s makeup concentration.
  4. Chip Filtration – Maintaining good filtration of your coolant. The chips that come off of your part are a contaminate. Keeping your coolant well filtered means these contaminates cause less damage to concentrations.
  5. Clean out Sump – Cleaning out your sump should happen periodically. When you do clean it out, it should be thorough and comprehensive


Divide 1 by the total number of parts (water + solution). For example, if your mix ratio is 8:1 or 8 parts water to 1 part solution, there are (8 + 1) or 9 parts. The mixing percentage is 11.1% (1 divided by 9).


(100 – the percentage): percentageFor example, if your percentage is 4%, take 100 – 4 (which is 96), so your mix ratio is 96:4 which is reduced to 24:1.

Following is a list of standard metalworking coolant concentrations and ratios


The good news

Sussex Tool and Supply has a great staff of Coolant specialist that are excited to discuss your coolant applications. We offer a complete coolant experience from additive selection to coolant maintenance. We also can ensure you never run out!

Contact us today and be worry-free with your coolant tomorrow!

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