Flow vs Filtration

There are 2 schools of thought here:

1. Those who want maximum oil flow and figure that any particles hitting the filter repeatedly will be mostly caught after a few passes. These folks want a filter to be as unrestrictive as possible - even if the media is rather "coarse" and permeable to debris.

2. Those that feel they want as much debris as possible to be caught as quickly as possible by a "fine" filter media, and are not concerned by the relatively small oil pressure drop across the oil filter.

Who is right?

This is something of a judgment call because there is a logic to both people's preferences. Personally, I lean toward the second school of thought because the first one assumes that a load of debris is put into the oil at one time with no more debris being added. In this case, the filter will likely catch almost all of the debris in successive passes. In reality, there will be a continuous generation of particulate debris as the engine is run. There will be carbon and sludge, and there will be wear particles and also dust getting into the engine that makes it past the air cleaner. This is why multipass tests generally show a lower efficiency percentage than single pass tests - "dirt" is being continually added to the oil going through the filter being tested.

I have seen little evidence that any correctly selected name brand oil filter is much more than "invisible" to the oil pressure system as a whole. There may be some exceptions for a few picky engines that use small, high efficiency filters, or in racing applications. I try to choose a happy medium between flow and absolute per pass filtration.

Some of my comparisons will show a 2 or 3 fold difference in time that is takes the filter center tube to fill with oil. This should not be taken as that there would be a 2 or 3 fold reduction in oil flow to the engine. I look at it this way: "Filter A" may drop 3 psi when "Filter B" would be dropping only 1 psi. But out of, for example, 60 psi oil pressure to the engine parts, it makes no real difference.
That is my theory anyway...and probably why I have seen no difference in after-filter oil pressure on my old van that has an oil pressure gauge.

Another thing is that just because a filter has a "fine" and efficient media, that does not preclude an easy passage of oil. There are wide variations in media composition, quantity, and media thickness in any given filter size. A filter with a larger quantity of media, all other things being equal, will pass oil more easily.

Whatever you choose...

Whichever type of filter you choose and whichever flow vs filtration characteristics you are comfortable with, it is my understanding that all oil filters must pass certain requirements. This is probably true, and a reputable filter that is advertised as meeting or exceeding car manufacturer or OEM specifications will likely serve you well in the long run.

Next: Filter Construction and Terminology