The ISO 4406 rating tells us the cleanliness level of our lubricant. It tells us the number of particles that can pass through a 4, 6 and 14 micron rating.
However, the value on the ISO rating does not represent the number of particles. On the contrary, it represents the range in which the number of particles can lie.
One key point to remember is that the rating will always change from the time that the sample was taken to the date that the results were processed.
Therefore, it is a good idea to use the sample result as a guide as estimate a bit higher for the real value of your lubricant.
Check out our article which goes into more detail about ISO 4406.
Usually, the OEM of the equipment specifies the filter rating (and even the filter material in some cases). These ratings help us to keep out particles of larger sizes that may cause damage to the equipment either through wear or clogging of fine clearances.
Some filters allow us to monitor the differential pressure. This is the pressure between the outside of the filters and inside and as this approaches the warning limits, we know that a filter change is needed in the near future.
However, there are times when there is no warning and the filter goes into bypass. When a filter goes into bypass, this means that the filter is no longer keeping back the larger particles. This can be catastrophic for the equipment as a higher concentration of contaminants can now enter the system and damage it.
It is common practice to change the oil filter when the oil is being changed. In some instance, (especially depending on the environment), OEMs recommend changing the oil filters twice or more before the actual oil change.
Always consult with your owner’s manual about the maintenance practices before adopting your own.
A lot of people get confused when reading the ISO 4406 rating. The rating specifies a range of the number of particles of certain sizes that can pass through 3 particular sized filters namely; 4micron, 6 micron and 14 micron filters respectively.
For instance; a rating of 13/11/8 indicates:
13 represents 4000-6000 particles over the size of 4um
11 represents a range of 1000-2000 particles over the size of 6um and
8 represents a range of 130-250 particles over the size of 14um.
These values are actually the number of particles per milliliter. It does not mean that you have 13, 11 or 18 particles only in your oil, it's much more than that!
There are different ratings for different levels of cleanliness.
If your numbers are really high (25/22/19) then there’s definitely a high level of contamination!
Different components have different ISO cleanliness ratings. For instance, a roller bearing has a higher cleanliness target than a Variable Vane pump.
Understanding the ISO 4406 codes are crucial for determining the steps needed in “cleaning up” your system lubricants.
However, when we test for the cleanliness of an oil, there are a couple things that we need to consider:
When testing, we have exposed the oil to the elements (highly dependent on the method of sampling)
Results are not instantaneous (even with an onsite lab, there will be a timeframe between collecting the sample and processing it)
Since there are lag times involved, the value that is reported for the ISO4406 rating is never really truly representative of the oil. As such, when analysing the results of this test, it is important to consider that the actual value may potentially be higher than reported.
