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An oil filter magnet is a magnet that attaches to an automotive canister type oil filter. It’s purpose is to supplement the oil filter’s mechanical filtration, by remove particles suspended in the motor oil, through magnetism or paramagnetism.

How Oil Filters Work

A typical automotive engine has a large pan on it's bottom, that serves as a reservoir for the engine’s lubrication oil. Inside this oil pan, is an oil pickup tube attached to the oil pump. When the engine is running, the oil pump draws oil from the oil pan, through the pickup tube, and distributes the oil to the various moving parts inside the engine. This oil lubricates the moving parts. However, not all friction is eliminated, there are some metal particles that wear off the parts and contaminate the oil. Combustion byproducts also contaminate the oil. As these materials accumulate in the oil, it's ability to lubricate is reduced, and wear increases.

Prior to the 1950s, most cars relied on frequent oil changes, to help the engine survive. In the 1950s, engine oil filters became more and more common, now all cars have oil filters. Oil filters prolong the life of the engine oil. There is now a much longer interval between oil changes.

Most oil filters are designed to trap particles larger than 30 microns in size. Inside the oil filter are pleats of cellulose or man-made fiber. This filter medium has tiny holes in it, that allow oil to flow through, while straining out particles larger than 30 microns.

To give some idea of how small these particles are, a human can range from 40 to 600 microns, with most being in the 40 to 80 micron range. The human eye can see particles as small as 40 microns, the size of the smallest human hairs. Talcum dust (baby powder) has particles as small as .5 microns. (See Figure 1)



As stated, oil filters remove particles 30 microns and larger, which is already microscopic. Some filters are a bit better, claiming to trap particles as small as 20 microns, which is quite good. Sometimes as time goes on, the filters get better, because the pores in the filter paper, become partially or totally clogged with these particles, and then only even smaller particles can get through. More often though, the smallest pores clog first, reducing the flow of the filter, while not straining out some of the smaller particles as well as could be filtered at first. Whichever way it goes, a clogged filter begins to starve the engine for oil. Filters can be made to strain out smaller particles, but if oil cannot get through, then the engine is starved of good, clean oil, and it will wear out shortly.

Because it is understood by oil filter manufacturers that a filter can become clogged and destroy an engine, they install bypass valves, so that the oil can go around the filter paper entirely. Of course at this point, the oil is no longer being filtered. What is worse is that the oil is also now washing the filter material's surface, and bringing the particles that the filter previously trapped, back through the engine again. This is why it is extremely important to replace your oil filter regularly.

While it may sound as though using an oil filter, and replacing it regularly, solves all the problem of contaminants and engine wear, it is not quite the case. According to the Society of Automotive Engineers, particles as small as 2 microns, still cause significant engine wear. Most engine wear and damage is from particles in the 10 to 20 micron range. It is also known that the bypass valves built into an oil filter, do not always work perfectly, often they leak some unfiltered oil and can allow particles of most any size to go through the engine. This is not often a significant source of engine wear, but on occasion, a large particle or particles, can go through this valve and scratch the bearing journals on crankshafts and camshafts, valve lifters and cam lobes, rocker arms and push rods and the like.

It is said that an oil filter reduces engine wear by some 95% on average, compared to engines with no filter, and frequent oil changes, however, it is a fact that engines still wear. Replacing or rebuilding engines due to that remaining 5%, is quite expensive.

Though engine wear cannot be eliminated, help is available. Engine replacement/rebuilding can be greatly postponed. Reducing this wear not only reduces or postpones expensive engine repairs/replacements, but it also enhances fuel mileage and reduces air pollution. It comes as no surprise that a worn out engine wastes fuel and pollutes more.

Oil Filter Magnets

Oil filter magnets work on the principle that most of the particulate matter which causes engine wear is composed of iron or steel. While this is true, it is not true that ferrous metals are the only source of abrasive materials in engine oil. Silica and coke (carbon) are non metalic combustion byproducts are also abrasive and find their way into engine oil. Also aluminum is commonly found in used motor oil, and although it is metallic, it is not magnetic. There are other abrasives found in used engine motor oil, but they constitute a smaller contribution to engine wear.

Magnets have been used to remove contaminants, from oil in engine oil for some decades now, and in industrial machinery since at least as far back as the 1930s. In the past, these magnets were more useful to detect problems, that they were effective at actually cleaning oil. The invention of Neodymium Iron Boron magnets in 1982, created the potential to change this. Originally, this magnet type was prohibitively expensive. However in recent years the costs have come down to where it is now practical to employ this technology in oil filter magnets.

Neodymium magnets are the most powerful magnets in the world. They are so powerful that they can pull very fine particles of metal from engine oil at a good distance. Other types of magnets cannot. Not only can they remove magnetic material, the can attract even many non-magnetic materials, such as aluminum, silica and coke, the major abrasive materials in used motor oil. This is done through a phenomenon known as para-magnetism, and also there is an effect wherein nonmetallic materials get "pinched" between magnetic materials and mechanically captured. Besides being more effective than other types of magnets, Neodymium magnets do not grow weaker with time. While other magnet type might be effective for a long time (50,000 miles or 10 years is claimed by some manufacturers), Neodymium magnets should last several lifetimes.

Design Considerations While the material chosen for oil filter Magnets is very important, the design (relating largely to intended physical location) is equally important. Understanding and examining the internals of an oil filter reveals why. Oil enters the filter through a series of holes near the outer edge of the canister, and then flows on the outside of the pleated filter material inside the canister. It then turns and flows through the filter material to the center of the filter and back out the center of the canister. In the closed end of the canister, is a valve mechanism. This valve prevents flow to the bottom of the filter under normal circumstances. The valve serves several purposes. It protects the filter from overly high pressures, which could result in bursting the canister or blowing out the o-ring seal, or tearing the filter material, all of which are bad things. It also prevents oil starvation when the oil is to thick to flow well through the filter media, due to low temperatures.

The potential causes of over pressure, would be usually be caused by one of two things. In cold weather, oil can have a high viscosity (the oil is thicker) and until the oil warms up, the oil pressure will be abnormally high. The use of proper, multi-viscosity oil, can go a very long way toward preventing this condition. The second cause of over pressure, is neglecting to change the oil filter as frequently as it should be. In this case, the filter becomes clogged and oil can no longer flow through the filter material. The job of the valve we just talked about, is to relieve the high pressures, by allowing the dirty unfiltered oil to bypass the filter material altogether. This is not good, but it is preferred to having the filter burst.

When the filter is clogged like this, the vehicle operator will not know that the oil is unfiltered, and will continue to drive the vehicle with unfiltered oil, prematurely wearing the engine out. This explanation of the insides and functions of the oil filter, helps us understand why some oil filter magnets are better than others.

First off, all oil filter magnets need two properties, the need to be strong enough to pull small particles from the engine oil from a distance. This requirement limits the use to Neodymium Iron Boron material. Less powerful magnets while providing some benefit are not effective at capturing very fine ferrous material or paramagnetic material. The second quality needed is temperature resistance. N.I.B. magnets may or may not meet this requirement. Some Neo magnets lose strength at elevated temperatures.

Oil filter magnet producers know this, and select a grade of Neodymium magnets to suit the purpose. Neo magnets come in different strengths as well, and the penetrating power of the magnet, is proportional to it's thickness. For these reasons, the addition of neo magnets of unknown characteristics to an oil filter, may not be very effective.

Regarding design in general and shape in particular, magnets sold as oil filter magnets, are most often either a flat disk or rectangle, a long thin cylinder, or an inline type. There are also ones that have some sort of mechanical attachment of several small, flat magnets to the side of the canister, ones mounted on hinges; there is even one that has a magnet on the bottom, attached to a spring that wraps around the side of the filter canister. There is also a type, that has a casing that holds a bunch of slender flat magnets side by side, that is formed around the curve. That one can be considered a curved magnet for the sake of our consideration here.

Table 1 shows the major differences to the consumer, of the most common magnetic filtration methods employed on automobile engines. It is not interned to be exhaustive or representative of any particular magnetic filtration device brands.



In Figure 2, there is an illustration which helps visualize what is being talked about as we discuss the different shapes of magnetic filtering devices.

The curved magnet, simply attaches to the curved side of the oil filter canister. The flat magnet is most often attached to the bottom of the canister. The cylindrical magnet is inserted into the oil outlet hole. The inline magnet filter, is clamped in a section of hose, usually requiring a way to create a routing of oil flow outside the engine, such as an adapter as often used when adding an engine oil cooler. Such adapters sandwich in between the oil filter and the engine. There is also an inline filter type that is a cartridge which is installed between the engine block and the oil filter.

The curved magnet, needs to have an inside radius such that any gap between the magnet and the canister, should not exceed. This gap (if any) should be less than .020 inches (about the width of a line drawn with a medium ball point pen) for best performance. A much wider gap than this and the side of the cannister interupts the magnetic lines of force to the degree that the magnet can no longer be very effective. This effect is known as magnetic shielding. (See Figure 4)    For this reason, curved magnets should be purpose made for oil filter work, surplus magnets are usually far from ideal.



Many manufacturers of flat oil filter magnets, recognize that a magnet in the center bottom, does almost no good whatsoever, and have offered a different approach. (See Figure 3)



This approach of several bottom magnets has some things to recommend it. It has the advantage of more magnetic area, but of course it increases the cost. It also concentrates the magnetic field into an area, where there may be more oil flow (though still not much) than there is with a center bottom mounted magnet. There is however, a possible added issue with this arrangement; the added power of extra magnets on the bottom, could potentially affect the pressure at which the bypass valve releases. This has not been established experimentally and it is probably not a problem, but it is something to consider. Flat magnets, wherever they are used, are also subject to the minimal gap rule (Figure 4).



In addition to insuring minimal gaps. The thickness of a neodymium magnet for oil filter use should exceed 1/3 of the distance from the outside of the canister to the deepest part of the pleats. For most automotive applications, this would mean having a magnet .200” thick or more. For optimum effectiveness, having a swept magnetic area exceeding 3 square inches is recommended. Some automobile owners change oil every 3000 miles religiously. This practice is a fine one, but unnecessarily expensive. Most cars under most conditions, can easily go over 2 to 4 times that distance between changes, even without oil filter magnets installed. Changing oil as frequently as every 3000 miles, wastes natural resources and adds considerably to the operationg costs of an automobile (over $2000 extra spent of the life of the car). Oil filter magnets not only can save you money on oil changes, but for those who are nervous about extended periods between oil changes, they can give one the confidence of knowing that magnet equipped oil filters clean the oil better than these frequent changes do. Skipping just one such too frequent oil change, will usually cover the cost of installing oil filter magnets, havnig the confidence to go with longer oil change intervals, and even filter change intervals, can really save a lot of money. Looked at in this way, not only will that engine last longer, but the money saved may even help pay for a new engine when it becomes necessary.

One many newer automobile manufacturers are recommending lower viscosity motor oils than was formerly the case. Pressure from C.A.F.E. standards, incentivises manufactures to find extra fule mileage where they cam. Lower viscosity oils improve fuel mileage, but result in thinner lubricating film thickness. This thinner oil film between metal to metal friction surfaces reduces clearances, making smaller abrasive particle control even more critical.

Manufacturers of Oil Filter Magnets (no endorsements implied): Magna-Guard (Cylindrical internal -ceramic) Filtermag (Segmented flat magnets mounted in a curve – Neodymium) Magnesaver (Curved single piece magnets – Neodymium) Performance Choice (Flat bottom type) Motion Pro (Magnetic Washer) Big Filter Plus (Flat bottom type) Bremmen Tech (Flat magnets inside rubber holder) Magnafilter (Inline filter, installs between block and filter) PowerMag (6 Flat side mount magnets in plastic holder) Forcefield (Inline filter, installs between block and filter) TurboMag (flat bottom type) Halex Development (Magnetized coil spring) One-Eye Industries – The Bear Trap (flexible holder of side mount flat magnets)