"How do filters differ when handling mineral oils versus synthetic lubricants? Also, how can you tell a good filter from a poor one?"
Selecting the right oil filter can be challenging, especially if the pertinent details are not provided. Even if you have the necessary information, you may not fully understand it. This can result in choosing the wrong filter for the application.
Please note that there are not separate filters for mineral oils and synthetics. Filters generally are classified by the type of media used. The two main media are cellulose and synthetic. Microglass and fiberglass are some of the other names commonly used in place of synthetic.
Cellulose filters are made from wood pulp with large fibers and have an inconsistent pore size. They aren't always the best selection because smaller particles can sneak through them. They are sometimes marketed as economy filters.
Synthetic filters are comprised of smaller man-made glass fibers and have a more consistent pore size. They do a better job of trapping smaller particles while still allowing oil flow. Synthetic filters also tend to not break down as fast as cellulose filters. They sometimes are marketed as having a higher dirt-holding capacity or as being longer lasting.
Once you have determined the best filter media for your application, it's time to look at the filter's capture efficiency. This can be confusing for those who aren't familiar with beta ratios and micron ratings. If a filter has an absolute rating, this means the filter is 98.7 percent efficient at removing particles at the stated micron size and larger. For example, if the filter is labeled as B25=75, the filter will remove 98.7 percent of 25-micron particles and larger. The filter will also remove smaller particles, just not as efficiently.
The term "nominal" may also be used to describe a filter's capture efficiency. Nominal is rated at 50 percent capture efficiency. When only a micron size is listed, e.g., 10 microns, the manufacturer is simply stating that the filter will remove 10-micron particles. However, this does not indicate how many of the 10-micron particles the filter will trap.
While industrial filters typically provide the necessary information to determine if they are appropriate for your application, automotive filters often do not. Therefore, when selecting an oil filter, consider using the general rule of thumb that the higher the cost, the better the filter. A few more dollars spent upfront can prevent costly repairs down the road.