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One Bottle Coolant Test

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One Bottle Coolant Test

A simple way to determine:
Amount and size of
particulate matter
Fungal and bacteria growth
Tramp oil and grease
Cobalt contamination


This is a very simple method to examine machine coolant quality.  You fill a clear bottle with machine coolant and let it sit.  You watch the changes over time to determine how dirty it is.   For other Machine Coolant Testing Methods, or For Machine Coolant Testing Instruments browse through our Machine Coolant Index.


You may see some settling in the first minute if you have really large particles.  If the machine coolant is very clean it may take two hours or more to get anything to settle out.  The best length of time would be to let the bottle sit for twenty-four hours.  New machine coolant will be clean with no sludge layer, no oil layer and no reddish color.


How to run the tests.

Test 1. Fill any clear bottle or jar most of the way to top with grinding machine coolant.
This is not a critical measurement. Label it with the time and source.  It might be a good idea to label the samples with the date, the machine, type of machine coolant, time since last machine coolant change and anything else important.


Test 2. How long does it take for particles to settle out?
See how long it takes for the particles to settle to the bottom. The finer the particles are the longer it will take to settle. Dust will float on top of and in water. Rocks will drop right to the bottom. This will give you some idea of particle size. If you get a thick layer immediately and nothing later then it is probably all particles over ten microns. If you do not get anything on the bottom in the first minute and the sludge layer grows over a day then you probably have particles that are all under two or three microns.


Typically you will get a pretty good sludge layer starting in a few minutes. That layer will continue to grow for up to an hour. After an hour it should be pretty well all settled out however, the really fine particles may take up to day to settle out.


Test 3. Measure the amount of sludge
Once everything has settled out measure the height of the particle layer on the bottom. A three-inch machine coolant sample can settle out to have as much as an inch or more of sludge on the bottom.


Test 4. Check the top for an oily layer.
Looking will tell you if you have tramp oils in your machine coolant. This is really simple but it is also very important. Oils and greases really clog filters and grinding wheels. Some machine coolants could be disposed of in sewers except for the oils and greases.


You may see three or more layers on top depending on what tramp oils you have in your machine coolant. It is possible to identify leaks in your system by observing the amount and kind of tramp oils


Test 5. Check the color of the machine coolant.
This is a test for metal contamination of the machine coolant and works best in clear machine coolant. In a lot of machine coolants the dissolved cobalt will cause a color change and a reddish or purplish tint. The amount of color change is related to the amount of dissolved cobalt.


Test 6. Cobalt levels and conductivity
The amount of color change relates to the change in conductivity of the machine coolant. This is important if it is being sprayed in sensitive areas. The amount of color change relates to the amount of chelated (sort of like dissolved) metals in the machine coolant.


Note: test conductivity with a meter. Other factors affect it besides dissolved or chelated metals.


Test 7. Look at the machine coolant.
If you see things floating in the middle of the machine coolant you may have fungal or bacteria growth.


Test 8. Shake the bottle
Once the sludge has settled out, shake the bottle and try to get the sludge back into suspension. A. This will give you an idea of how much sludge there is in relation to the ability of the machine coolant to carry sludge. B. You will also get an idea of the amount of oiliness by how well the sludge sticks to the walls of the bottle.


Typically it will be impossible to shake the bottle enough to get all the sludge back into suspension.