If motor oil is the lifeblood of an engine, the oil filter has to be its kidneys. There are thousands of small engines on the market that live in dirt bikes and race engines that do not employ an oil filter, because the engine is being taken apart for rebuild before any damage would occur anyway. But for automotive engines for the consumer and commercial market, where expectations of engine longevity are in the tens of thousands of hours, keeping oil clean between changes is vital.
Motor oil serves the purpose of not only lubricating the bearings and rings of the engine, it also serves as a way to remove heat from the engine in places that coolant cannot get to—like the piston rings. Due to the engine oil’s exposure to the combustion chamber, and things like piston ring blow-by, oil is frequently contaminated with post-combustion byproducts of petroleum burning. With how clean engines run these days and the quality of oil manufactured, the 3,000-mile oil change is ancient news.
The function of full-flow oil filters for the automotive application is pretty simple, and are made up of just a handful of components. The casing on the outside is made from stamped steel, and it houses the bypass valve and filter media. Oil flows into the filter through the outer ring of holes that are viewed on the face of the filter. After the oil passes through these holes, fills the outer portions of the filter casing (under pressure from the oil pump), and is forced through the media filter into the core of the filter itself. Once the oil has been cleaned by the filter (25-30 microns range) it then flows back towards the top of the filter through the center and into the engine. In the event that the filter media becomes clogged, a bypass valve will open making a full loop of the filter, bypassing the filter media to ensure that the bearings remain lubricated. Unfortunately, this means that no filtering is happening if the bypass valve is open, but the engine can remain lubricated.
With all that said, however, no oil filters are made the same. There is a huge range of filters from $2 up to $30, name brands and ones you have never heard of and more than likely if you are buying the filter yourself, you think that the more expensive the filter, the better it is made. That is not always the case, however, and it behooves you to make yourself educated on filters if you want the best for your engine. Generally speaking, WIX XR series and the high-end FRAM and Purolator offerings are continually the highest quality consumer and commercial filters on the market. It is worth noting though, that some industrial grade filters from Caterpillar and Fleetguard can be adapted to consumer and commercial automotive engines in some instances, and your local friendly internet forum will probably have the parts numbers for you on that.