STOLEN FROM ANOTHER WEB SITE, I DID NOT WRITE THIS
If you do any research on your own, you'll find that most manufacturers no longer use micron levels to rate their filters. This is a result of some manufacturers' shady representation of their filters using micron ratings. You see, some filter manufacturers would indicate that their filters would remove x micron particles and leave it at that ("x" being whatever arbitrary number they chose to print). Of course, consumers would take this to mean that all particles larger than this micron level would be removed, which is not necessarily the case.
The truth is that chicken wire will remove 5 micron particles. It will even remove 1 micron particles. BUT, it will not do so with very good efficiency. The key is, how efficient is the filter at removing x micron particles. If you don't know how efficient it is at a certain level, the micron rating means nothing.
So, most companies have gotten away from micron ratings (to avoid the confusion) and have gone to an overall efficiency rating. In other words, an industry standard test is used in which oil is contaminated with a certain number of particles of varying micron sizes. At the end of the test, there is a measurement taken to determine the total percentage of ALL of these particles that were removed by the filter. That percentage is then stated as the overall filtration efficiency of the filter.
Some companies use a single pass test, others use a multiple pass test. Both are perfectly valid and will give you an excellent way of determining how well a filter will do its job, but you should not try to compare results from a single pass test to results of a multiple pass test. You'd be comparing apples and oranges. In either case, high efficiency filters will rank in the low to mid 90's for filtration efficiency. Off-the- shelf filters will rank in the mid 70's to mid 80's for filtration efficiency.
IF MICRON LEVELS ARE TO BE USED
Nevertheless, you may still want to compare filters using micron ratings. If this is the case, the following is a good rule of thumb. A filter is considered nominally efficient at a certain micron level if it can remove 50 percent of particles that size. In other words, a filter that will consistently remove 50% of particles 20 microns or larger is nominally efficient at 20 microns.
A filter is considered to achieve absolute filtration efficiency at a certain micron level if it can remove 98.7% of particles that size. So, if a filter can remove 98.7% of particles 20 microns or larger, it achieves absolute efficiency at that micron level.
Most off-the-shelf filters are based upon a cellulose fiber filtration media. Most of these filters are, at best, nominally efficient at 15 to 20 microns. They won't generally achieve absolute efficiency until particle sizes reach 30 microns or higher.
High efficiency oil filters have filtration media made of a combination of at least two of the following: glass, synthetic fibers and cellulose fibers. Those that use all three are generally the best in terms of filtration. Those that use only two will fall somewhere in between. The best of these high efficiency filters will achieve absolute efficiency down to about 10 microns and will be nominally efficient down to 5 microns or so.
HOW IMPORTANT IS BETTER EFFICIENCY?
The fact is, you would probably be amazed at how much engine wear could be eliminated simply by using more advanced oil filtration. In paper 881825 the Society of Automotive Engineers indicates that a joint study was performed between AC Spark Plug and Detroit Diesel Corp. The study found that finer oil filtration significantly reduced the rate of engine wear.
According to the paper, the tests regarding engine wear within a diesel engine were performed using four levels of oil filtration. They chose filters whose efficiency rating was very high for particles of 40 micron, 15 micron, 8.5 micron and 7 micron sizes.
The same was done for gasoline engines, except that the relative sizes were 40 microns, 30 microns, 25 microns and 15 microns.
To make a long story short, the researchers had this to say:
"Abrasive engine wear can be substantially reduced with an increase in filter single pass efficiency. Compared to a 40 micron filter, engine wear was reduced by 50 percent with 30 micron filtration. Likewise, wear was reduced by 70 percent with 15 micron filtration."
By combining this type of oil filtration with the superior protection and cleanliness of a premium synthetic oil, you will virtually eliminate engine wear.
EFFICIENCY IS NOT THE ONLY IMPORTANT FACTOR
Of course, filter capacity and quality of construction are also important considerations. If a filter has low capacity and high efficiency, it will clog up quickly. As a result, your oil will begin to bypass the filter completely and will become contaminated very quickly. Filters with high efficiency and low capacity should definitely be changed at 3,000 to 5,000 miles or 3 months - without question.
Filters which have high capacity but low efficiency will last longer without becoming saturated, but will not protect your engine as well. Of course, filters with low capacity AND low efficiency are at the bottom of the barrel and should be avoided. Generally, you can call a filter manufacturer and ask them specifically what their filtration efficiency and capacity ratings are for your filter. They should have that information.
If they give you a micron rating, ask them how efficient their filters are at removing particles of that micron size. You might also ask them at what micron level their filters are nominally efficient (50% removal) and at what level they achieve absolute efficiency (about 99% removal). If they can't or won't provide you with a straight answer, I wouldn't purchase their filters.
If they give you an overall percentage efficiency rating, ask them if that is for a single pass test or a multiple pass test. That will be important if you are to compare those ratings with other manufacturers so that you'll be comparing apples to apples.
This is nearly 10 year old info but explains the rating system pretty clearly. Again not mine. I lifted it from his site. http://www.autoeducation.com/autosho...l-change-7.htm