This guideline provides a method for an accurate measurement of particle count by pretreating oil samples with kerosene, prior to testing, with an optical light-blocking automatic particle counter. The particle counts are then corrected for the pretreatment and an ISO code is determined for the oil sample.

Table 1. Tooling and Equipment

The Impact of Additive Interference
In certain oils offered by original equipment manufacturers and oil suppliers (mainly diesel engine oils and hydraulic oils), oil additive interference has caused some difficulties in determining new oil cleanliness levels with automatic optical particle counters. Because of this interference, the oil may appear dirtier than its true cleanliness level without additive interference.

The oil pretreatment method described in this article provides step-by-step instructions that will allow for the comparison of oil cleanliness results from both nonpretreated and pretreated oil samples to determine if additive interference is impacting particle counter results.


Figure 1. Clean Sample Bottle
(1) The 50 ml (1.7 ounces) line is in the middle of this ridge in the bottle.
(2) The 100 ml (3.4 ounces) line is just below the top of the "Fill Range" line.

Test Procedure
Step 1 - Filter 100 milliliters (3.4 ounces) of kerosene through a filter patch to ensure cleanliness of the solvent by using the filtering procedure described in the Tool Operating Manual, NEHS0729,"Use of Portable Contamination Control Kit." Caterpillar recommends that the 0.45-micron filter patch be used in conjunction with the portable contamination kit. Each oil sample analyzed will be split into two separate samples, and each sample will require 50 ml (1.7 ounces) of filtered kerosene.

Note: The best choice to filter the kerosene is to use a 0.45-micron patch. The patches can be ordered through Fisher Scientific and cost approximately $67. The Fisher Scientific part number is 09-905-15 for a pack of 100. If the 0.45-micron patch clogs, you should first filter the kerosene with a five-micron patch, followed by a 0.45-micron patch. If the clogging is a result of water, start over with a new container of kerosene.

Step 2 - Fill two of the clean (super-clean rated) oil sample bottles to the top (fill range line) with the oil to be tested. One sample will be tested without pretreatment and one will be tested with the pretreatment oil method. All of the sample bottles should be rinsed with the oil being tested. (Refer to training video PERV4638, "Caterpillar Oil Sampling ... The Right Way.")

Note: The source container of the oil needs to be agitated before the oil is poured into the small sample bottle. If the sample is taken before agitation, then the concentration of particles will be altered and incorrect. For example, 3.78-liter (one U.S. gallon) and 18.9-liter (five U.S. gallon) containers should be shaken for three to five minutes before a sample is taken. It is recommended to use a paint shaker-type of device to agitate the container. Hand-shaking will not be adequate to resuspend the particles and, thus, may affect the results.

Step 3 - Shake one of the two small samples vigorously for one minute to ensure proper agitation of the oil. One minute of agitation may be adequate only if the original oil container was properly agitated within the last couple of minutes. Significant particle settling can occur within five minutes. Noria information suggests that five minutes of hand-shaking resuspends only 78 percent of the particles and that a paint shaker is needed to ensure resuspension of 98 percent of the particles.


Figure 2. Bransonic B200 Ultrasonic Bath

Step 4 - Take the shaken sample and unscrew the lid one quarter of a turn. Place the bottle in the ultrasonic bath for 45 seconds to remove the air bubbles. It is acceptable for air bubbles to remain at the surface of the oil.

Note: The ultrasonic bath should be filled with enough water to cover 75 to 80 percent of the height of the bottle, which allows the air bubbles to rise to the top of the oil in the bottle.

Step 5 - Remove the sample bottle from the ultrasonic bath and analyze the oil sample immediately, using the particle counter per the manufacturer's instructions to obtain the particle count results. This sample will be used as a reference to determine if additive interference is present in the oil.

Note: As a reminder, the three-code readout represents the counts for the 4-, 6- and 14-micron particles, respectively. For new oil, only the values for the second and third codes are reviewed. These codes represent the values for the 6-micron and 14-micron particles. Caterpillar does not currently use the 4-micron rating to determine oil cleanliness.

Step 6 - Take a third clean sample bottle and mark the levels on the bottle at 50 ml (1.7 ounces) and 100 ml (3.4 ounces) (Figure 1).

Note: If using a different type of sample bottle than the part number listed in Table 1, the 50 ml (1.7 ounce) and 100 ml (3.4 ounce) levels will need to be determined before beginning the procedure.

Step 7 - Take the second oil sample bottle from Step 2 and shake the sample vigorously for one minute. Pour the oil into the empty sample bottle from Step 6 to reach the 50 ml (1.7 ounce) mark on the bottle. Both sample bottles should now contain 50 ml (1.7 ounces) of oil.

Step 8 - Add 50 ml (1.7 ounces) of the filtered kerosene from Step 1 to both sample bottles. The bottles should now be filled to the mark for 100 ml (3.4 ounces). Mark one of the sample bottles as "Flush" and the other as "Sample." Both of these samples are now considered as pretreated or diluted.

Step 9 - Vigorously hand-shake the pretreated oil sample marked "Flush" for one minute.

Step 10 - Take the shaken sample and unscrew the lid one quarter of a turn. Place the bottle in the ultrasonic bath for 10 to 15 seconds to remove the air bubbles. It is acceptable for air bubbles to remain at the surface of the oil.

Step 11 - Remove the oil sample bottle from the ultrasonic bath. Immediately analyze the sample using the particle counter per the manufacturer's instructions.

Step 12 - Repeat Steps 8 through 11 for the bottle marked "Sample."

Note: The two pretreated samples are run through the particle counter because one sample is used to flush the system with the same type of fluid that is being analyzed to ensure a more accurate particle count.

Step 13 - Because the sample is only 50 percent oil, the particle count results for the dilution factor can be corrected by multiplying the counts per ml by two, or by adding one number to each range of the ISO code. Therefore, the number of particles in 100 percent oil would be two times as much as what is counted in a 50 percent oil sample. Refer to Table 2 to determine the corrected ISO code from the counts per ml numbers. This can also be accomplished by adding a value of one to each ISO code number. For example, an ISO 17/14/10 pretreated sample has a true cleanliness of ISO 18/15/11.

Step 14 - Compare the nonpretreated and the corrected pretreated ISO codes. If the ISO codes are the same, there is no significant additive interference and the particle count determine is accurate. If the pretreated sample is lower (cleaner) by at least two ISO codes, additive interference has occurred.

Note: Regardless of pretreatment, be aware that water in the oil samples will cause inaccurate particle count readings.

Table 2. Corrected ISO Codes

Equipment Notes
The ultrasonic bath should meet the minimum specifications listed in Table 3. There are several different brands available that can be purchased at retail stores. For example, the specifications in Table 3 are for a Bransonic model B200 and can be purchased online through the manufacturer for approximately $105. The manufacturer's Web site is

Table 3. Ultrasonic Bath

Courtesy to Caterpillar for permission to use the dilution method (SEBF9086-01) for Noria's publishing and training purposes.

The author also wishes to thank a team from Exxon Mobil for their assistance with the initial testing procedure.