Lesson 271 - Coolant Maintenance Troubleshooting

Troubleshooting coolant problems

helps you better understand coolant maintenance protocols as well as equipment that solves coolant problems. We’ve arranged this troubleshooting Topic by product to compare the technologies we offer and how they fit into the grand scheme of coolant maintenance.

pH Test Strips

“Why is it important to check the pH of coolant (and what is pH anyway)?”

Put simply, pH is an indication of the acidity or alkalinity of a fluid. Water has a pH of 7, which is neutral. An acidic fluid will range from 0-7 pH, and an alkaline fluid will have a range of 7-14 pH. pH levels of coolant drop due to bacterial emissions, so coolants are deliberately formulated within the pH range of 8-10 to counteract bacterial growth. Even a .2 drop in coolant pH can cause a host of problems, ranging from rusty machines and parts to sump odor and skin irritations. With consistent pH monitoring and other bacterial control methods such as oil skimming and aeration, these problems can be prevented.

Measuring the pH of a sump rinse cycle using

before it is recharged with fluid also helps to ensure that the fresh batch is not subject to the poor conditions which made it go bad in the first place.

Hardness Testing Sticks

“My coolant separates from the water after mixing. Why?”

The water source contains excessive minerals and is ‘hard.’ On a chemical level, these minerals prevent concentrate from mixing with water. Even with a ‘soft’ water supply, minerals build up over time at the sump level due to evaporation.

Most coolant manufacturers specify what hardness range their blend operates within. Use

to check the water supply and compare its hardness to the specifications of the coolant. Then, monitor hardness at the sump level at least once per week.

RO (reverse osmosis) or DI (de-ionized) water sources may be needed should the initial water source be near the upper range of what the coolant can bear. The ‘hard’ water source may not affect the initial charge, but will certainly affect the coolant as refills are repeatedly added at the sump level.

Hard water can also contribute to surface grease formation, which is not readily removed by mechanical skimmers since its surface tension is different than straight oil. (Coalescers work better here.) Grease also contributes to premature filter blockage. Other negative results of hard water are rust and gummy residues on parts or machine interiors.


“Do I need to replace the refractometer if it is blurry?”

No. Like binoculars, the instrument may need to be focused. But if the coolant reading ‘line’ is blurry, it is because of emulsified oils in the coolant sample. Replace the coolant batch if there is no discernible line to determine what the concentration is.

“How do I know what refractometer scale I need?”

use a scale called Brix, which was designed for measuring sugar content, but is also used for metalworking fluids. Some coolant manufacturers blend their coolants so they measure 1:1 with the Brix Scale. Some do not. Check the product data sheet for the coolant’s ‘refractometer factor’. This factor needs to be multiplied by the scale reading to determine the actual percent concentration of the coolant mixture. To determine which refractometer scale is the best, first divide the target concentration by the coolant’s refractometer factor. For example, the factor is 1 and you need a 10% target concentration. A scale that goes up to 10 is sufficient (10 / 1 = 10). But, if the factor is 0.8 and the target is 12%, you need a scale that goes at least to 15 (12 / 0.8 = 15). However, we recommend you use a scale that has a higher range than what you are trying to achieve as a target, since evaporation at the sump level will increase the concentration. You will then be able to read these higher values and make appropriate corrections for them.

Venturi Mixers & Proportioning Pump

“Why can’t a

 deliver the mixed fluid through a long piece of hose or pipe?”

The venturi mixers use the water source to create the vacuum which suctions the concentrate. When a long hose or pipe is installed on the outlet, the energy of the water pressure pushes that long column of fluid, and the ability to suction the concentrate is inhibited.

When long distance is required, use the

. It uses the water pressure to drive a reciprocating piston and valve system to suction a given amount of concentrate and a given amount of water on each stroke. With this action, known as positive displacement, the coolant-to-water volume is protected and can be delivered at longer distances.

“Why do you recommend the protective accessories with the Proportioning Pump?”

The water filter will prevent minerals, or scale, from building up on the small internal pump components. This will lessen wear and extend its performance.

The water limiter protects pump components from damage due to excessive incoming pressure.

The back flow check valve prevents mixed fluid from traveling back through the pump and into the concentrate, particularly when the water source remains on at all times or if the mixture is delivered vertically.

Mechanical Skimmers

“What are the benefits of using the Diverter?”

A mechanical skimmer loves oil and does not know the difference between good oils in coolant and bad tramp oils. It will pick up anything it recognizes as oil…period.

The Diverter does know the difference, separates oil from coolant in its reservoir, and diverts coolant back to the sump. Only tramp oil goes to the oil waste container, saving hundreds of dollars a year in otherwise wasted coolant.

If access is an issue and the Diverter will not fit, the skimmer can be put on a timer so it runs only as long as an oil layer is present. Once the tramp oils are picked up, the skimmer turns off. This also will save motor life.

“What factors should I look at when choosing a mechanical skimmer?”

Access to the area where oils naturally collect (mount location of the skimmer)

Reach needed to the lowest fluid level (distance from mounting point to low fluid level)

Required rate of oil pickup (quarts or gallons per hour)

Temperature of the solution (as in wash water)

If using a mechanical skimmer, we recommend the use of the Diverter whenever possible.

If the sump runs only one or two shifts, an Oxygenator assists in aeration while the machine pump is down. It will help to prevent bacterial rancidity by keeping oxygen in the fluid.


“What is the benefit of using a coalescer over a mechanical skimmer?”

A mechanical skimmer only removes tramp oil and needs regular maintenance to keep chips and other debris off the pickup mechanism and scrapers.

The Muscle Coalescer, when dedicated to a sump, will constantly remove the oil layer and keep the coolant sump in circulation when the machine is idle, helping to prevent bacterial contamination which degrades coolant. Little to no maintenance is required, except filter bag replacement on chip filtering models. If floor space is at a premium near a machine, a mechanical skimmer may be a better option to remove tramp oil, then an Oxygenator whenever the pump does not run to help keep bacteria at bay.

“How do I know a coalescer will effectively separate tramp oil from my coolant?”

Coalescer efficiency is all about how long it holds the coolant versus how much oil gravity separates from the coolant within this time.

When new, most coolants will reject tramp oil within a matter of minutes. This is the best time to start using a coalescer, preventing emulsification of tramp oils. But to prevent waste, you can determine if a coalescer will work well on a used coolant batch. In a clear container, such as a water bottle, take a small sample of the fluid. Cap the bottle, shake it well, and then wait 15 minutes (for the Muscle). Whatever oils are rejected within this time are those that the coalescer will separate. Let the sample sit longer to see if there is oil that takes longer to separate. If there is additional oil, this sump should be changed as soon as practical since the coalescer will only recirculate oil back to the sump.

Note that high-pressure coolant delivery systems, such as for through-spindle coolant, cause tramp oil to deeply emulsify into coolant because of pressurization. During the separation test, you may see a separated layer that looks like a milkshake or sponge. This layer is made of lots of tramp oil, a bit of coolant, and tons of air bubbles, and is what you can expect as a tramp oil layer.

Conclusion to the Intermediate Course

We hope you agree that this part of ZCMC has lots of information that will enhance your ability to spot and solve coolant problems, and even help the customer prevent them. Thank you for the time you have spent learning more about Zebra and what has made us successful over the last two decades. We’re glad to have you as a soldier in the field and look forward to hearing from you when we can help!

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