Used oil filters provide lots of clues about the oil condition. Inspecting a dissected filter reveals information about the filter itself when looking for collapsed media, bad seals or weak points that developed during use. The debris remaining in the used filter also indicates important facts about the machine’s health.

Here, we discuss three different options for analysing this filter debris. The first method is quick, easy and free, and can be conducted on site. The next two involve the use of laboratory instruments. You can choose which debris/ filter examination method you need depending on how much detail you require.

Canister filters

For a canister style filter, a cost-effective, easy technique is to simply cut the filter in half, and remove the media. Then, conduct a visual inspection of the media, for sludge, varnish or shiny particles. An additional step at this point would be to use a magnet. This is a good way to determine whether any of the shiny particles are metallic.


For a more scientific version of this method, the media can be extracted from the filter following the above technique, and then submitted to a reliable laboratory, where it will be analysed by trained technicians. Several methods are used in the laboratories, including separating the debris from the filter media using ultrasonic agitation

Once the debris is separated, the size of the contaminants is assessed, counted and categorised, and many additional condition monitoring tests can be conducted to determine the machine’s health.

Extract the oil

Thirdly, a different option is not to remove the filter media, but rather to drill a hole into the filter canister to extract the oil. This is then collected in a sample bottle, and visually inspected with a laser beam for particulate matter. When inspecting with a laser, safety is of paramount importance.

Similarly to method one, a magnet can be employed to show whether any of the particles are metallic. Again, the sample can be submitted to a laboratory for more detailed, scientific testing.

ASTM D919-14 is the standard guide for filter debris analysis using manual or automated processes. This standard can be reviewed for a more detailed, step-by-step process. 

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