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Filters are an integral part of the oiling system in your engine. They provide a catch point for trash and dirt that are found in any engine oil after operation. Engine blow-by transfers partially burned fuel (which is highly reactive) and water into the crankcase, where they interact with the engine oil to create some pretty nasty compounds. If these are allowed to remain in the oil, they find their way onto metal surfaces and into nooks and crannies where they generally cause decreased engine performance and poorer low-temperature flow properties, and prevent additive components (antiwear, antifoam and pour point depressants) from doing their job properly. The oil filter is there to remove the products of these reactive compounds and insolubles before they can do damage to your engine.

The history of the oil filter is an interesting one. The first engines didnt have a filter, but had a metal screen on the oil pump intake. Todays engines still have that screen. In 1923, Ernest Sweetland invented the original Purolator oil filter, considered to be the first modern oil filter. It was more sophisticated in design and was located between the oil pump and the engine lubricating points. However, it was fixed in place and bypassed most of the oil. That is, only some of the oil was filtered on each pass through the system.

The give and take here is that dirty oil is better than no oil and if all of the oil passed through the filter, the medium would eventually become completely blocked and the engine would then starve for oil. It took 20 years to come up with a full-flow filter that would take all of the oil through the filtration medium. Of course, that was only so long as the oil flow was not too restricted. When that happened and pressure mounted, a bypass opened so that oil would continue to flow.

Some of the reasons why the bypass would open were that the filter was clogged with debris, or the oil was too thick to pump successfully through the filter due to cold weather, or the oil was too thick because of oxidation. At least the bypass allowed oil to get to the engine.

Evolving Designs

In 1954, Wix created the first true, easily detachable spin-on filter which is now the standard, at least sort of. If you have ever seen a filter catalog, youll know that just about every engine has a different design with varying thread sizes (in both English and metric), different can shapes, and internal vs. external connections. Some are extremely similar in external dimension with the only difference being thread size. This leads to situations in which a filter seems attached to the engine, but falls off rather easily and with disastrous results for the engine -no oil! Believe me, I know this happens.

So, given the basics (spin-on filters, bypass filter designs and full-flow filters), lets look at some of the more interesting permutations and combinations that have occurred.

A number of filter media have been tried in addition to the treated cellulose (paper) most commonly used. One of the more famous is toilet paper. The Frantz bypass filter, first developed by George Walker in 1962, uses a roll of toilet paper as a depth-type filter medium.

The rationale for TP is that it has a very fine porosity and a roll is quite thick (4.4 inches), thus filtering even the smallest of contaminants out of the oil as well as up to 6 ounces of water. The aftermarket housing for this bypass system is designed to hold a standard-size TP roll and is said to be easy to install and maintain. The paper choice is tightly wound, and firm and hard when squeezed. (Im just quoting from Frantz literature!)

There is little or no test data but some of the testimonials to the value of the Frantz filter indicate that the used oil is very clean even after several thousand miles of use. In fact, claims of annual replacement are common, as well as reduced insolubles, etc.

Of course, there is a flip-side to all of this. The following objections have been raised to the Frantz:

1. The TP will fall apart leaving lots of fine fibers in the oil. Frantz fans say, no way. They point out that full-flow filter media are paper as well. They also make the point that TP is actually stronger when wet with oil. My take on this is that TP is supposed to dissolve in water, making it possible to be degraded in sewage plants. The question is whether or not oil will also cause it to break down.

2. TP does not belong in an engine filter. Theres no response to this except to say dont use it if you dont like it.

3. Use of a bypass filter will void your warranty. This is probably not so, but should be taken up on a case-by-case basis with your dealer.

4. Too much trouble and expense to install the system and change the cartridge. I guess this is true if you dont change your filter now but it probably isnt the most difficult thing to do.

The bottom line is that I dont think that TP and engine oil mix ideally. Since the OEMs like the current filtration systems, thats good enough for me. Ive seen many vehicles which have gone for lots of miles without fancy filtration systems.

Cotton, Clay and More

Another filter medium that has been used is clay. This requires an elaborate system which circulates oil through a clay contactor which adsorbs particulates and other debris; its used in some industrial engines and turbines. The concept is good – its basically what an oil rerefiner uses to clean up used oil – but the oil volumes in a passenger car arent large. Also, todays modern rerefiners go on to hydrotreat the oil, which hasnt been suggested by anyone yet as an on-board filtration option.

Yet another filter medium which has been used is waste packed cotton. This material is certainly a good filter medium and has wide use in the filter industry. It does however, have a history. About 25 to 30 years ago, there was a problem with waste packed cotton filters that showed up in Cummins engines. The engine oil extracted some of the natural oils found in the cotton (apparently, it wasnt washed to any great extent). Engine oils contaminated by these filters turned out to be very corrosive to copper surfaces.

In fact, this problem led directly to the development of the Cummins HTCT procedure. This test measures the ability of engine oils to protect against corrosion on copper, lead, and tin metal surfaces. For a time, Cummins specifically banned any engine oil containing molybdenum (moly) since the oils in use when this situation occurred did contain moly.

Of course, the filter medium used in most current full-flow, spin-on filters is treated paper. It is pleated to provide added surface area and is about 0.1 inch thick. It serves to remove the greatest amount of contaminants and has been in wide use for many years.

Newer to the market, costlier and usually made by the same filter manufacturers that make the cellulose versions, are synthetic filter media. These employ a nonwoven synthethic fiber such as polyester, which is melt-bonded into a mesh-like sheet and then pleated and formed to fit into a spin-on cartridge housing.

Recent Innovations

There are other types of filtration devices available. Centrifugal systems rely on the flow of oil to rotate the filter inside a housing, where insolubles and other particulate matter are slung to the walls of the housing and isolated. This device is used on bypass filters and is most often seen in heavy-duty truck applications and stationary engines.

Magnetic filtration is another type used in engines. Most often, this is either the drain plug itself or is a device that sits between the oil pump and the oil filter. The obvious intent is that the magnet removes any ferrous metallic particles. Such wear debris can be damaging to moving parts within the engine. One typical device is the Boss Magnafilter.

There is another approach to filters that is very interesting. In the late 1970s, Monroe Auto Equipment proposed the addition of a polymer ring, which was impregnated with additives, in the filter housing above the filter medium. The ring would dissolve in the oil over time, introducing a polymeric V.I. improver into the oil. The polymer concept had been developed by DuPont, which had also developed the idea of including some additive components to augment the oils performance and extend its life.

Unfortunately, this didnt get off the ground since the polymer ring dissolved too quickly.

Since that time, a number of improvements have been proposed. One concept from 1993 was the addition of PTFE – best known as the non-stick coating Teflon – to the filter. The polymer would be dissolved in the oil over time providing additional wear protection and friction modification. An extension to this concept came around 1997 and included other additive components besides the PTFE. Other proposals have included a heater in the filter, to separate water from the oil and to help solubilize additive material which was built into the filter.

In 2000, PTFE was proposed to be built into the fabric of the filter medium itself, to aid in controlling the rate at which the polymer was dissolved in the oil. Five years later, the form of the additives was changed to an oil soluble gel which was incorporated into the filter and allowed to solubilize at a controlled rate.

Most recently, Donaldson Co. has incorporated a container of additive into its heavy-duty engine oil filters, which it claims will double engine oil life. It believes this concept will help with exhaust-gas-recirculation engines which tend to deplete additives more quickly. The additives in the filter increase Total Base Number and, apparently, delay Total Acid Number increase. The release of the additive components is at a controlled rate.

Donaldson points out that this system doesnt require any changes to the equipment, since it is a direct replacement for their current filters.

End of Story?

No discussion of filters would be complete without mentioning disposal. Obviously, the used filter is full of used oil, which is a very bad actor in the environment. The two ways to properly manage used filters are to either hot drain them thoroughly, or actually use a crusher to squeeze the oil out of them. In each scenario, the filter then must be disposed of in an environmentally acceptable manner. The cans on the filter are recyclable so there is a home for them.

Engine oil filters have come from a screen on the oil pump outlet through a bypass filter built into the engine to a replaceable spin-on, full-flow filter. From there, the filter has been doctored with additives, boosted with magnets and centrifuges, and filled with different filter media.

Im sure that the filter is bound to have even more tweaks applied in the coming years. What will happen next? Well just have to stay tuned.

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