Automotive oil filter magnets have been around for nearly as long as the internal combustion engine—so what makes us skeptical of their purpose?

They can be expensive for one thing. They must also be transferred from the old filter to the new one every time you change oil. They are not always completely understood.

Are Oil Filter Magnets Worth the Investment?

(Image/Jim Smart)

We can tell you oil filter magnets are worth the investment in what they provide in engine and driveline protection. They capture ferrous metals (iron and steel particles) in the filtration process to keep harmful magnetic metal particles away from your engine’s precious moving parts. They’re also perfect for driveline components.  

Magnetic filtration is available for virtually every type of oil filter imaginable. (Image/Jim Smart)

FilterMag tells us with the tight tolerances of today’s engines and transmissions, normal wear and tear generates iron and steel particles that remain suspended in oil. These particles are so small they can pass through the best oil filters. As hot oil circulates back to the oil sump, these iron and steel particles are carried back into the engine’s oiling system. With an oil filter magnet, these particles become trapped on the inside wall of the oil filter and are thrown away when you change the filter.

It has been proven the removal of very small iron and steel particles (10 microns) from lubricating oil has a very positive effect on engine life. The finer the filter element, the more beneficial good filtration is for longevity. Add a filter magnet and the result becomes even more beneficial.

Because FilterMag is magnetic, it “jumps” right onto your oil filter with aggressive magnetism trapping ferrous metal particles that pass through the filter. (Image/Jim Smart)

How Do Oil Filter Magnets Work?

In order to understand what filter magnets do, you must first know something about metal. Not all metals are magnetic, meaning they are “non-ferrous” metals. Non-ferrous metals are aluminum, copper, lead, zinc, tin, gold, silver, and even some diecast. These metals are not magnetic and cannot be trapped by a filter magnet.

(Image/Jim Smart)

Ferrous metals, with a few exceptions such as some stainless steel alloys, are magnetic and can be trapped by a filter magnet. Steel alloys consist of a cocktail of metals designed to make steel stronger. We create a steel alloy via the infusion of chromium, nickel, titanium, and other metals to get greater strength and durability. Titanium enables us to produce lightweight steel, which is especially important in aviation and racing for both strength and weight reduction. Stainless steel is an alloy produced using chromium primarily. It is typically non-magnetic depending upon the alloy mix and it is corrosion resistant.

And yes, you can install two FilterMags for even greater engine protection. (Image/Jim Smart)

Just plain old-fashioned steel is made from iron with a carbon mix to harden the iron. This process begins by heating and melting iron ore in blast furnaces. The melted steel comes out of the furnaces and is poured into molds to form ingots used in the manufacture of steel products. High carbon steel has a higher carbon content compared with other types of steel, which makes it stronger. Cast iron used for engine blocks, heads, cranks, and even camshafts comes from raw iron, carbon, and silicon to give it strength. There are several forms of cast iron depending upon the strength desired.

Stray iron particles from castings can eat away at bearing and journal clearances, score cylinder walls and piston skirts, damage piston rings, score cam lobes and journals, and eat away at the oil pump. Iron particles originate primarily in poorly cleaned and serviced iron castings and parts. At that, you can be thorough in your cleaning and still wind up with destructive metal particles floating throughout your engine’s oil system, which is all the more reason to use a filter magnet.

Popular Types & Uses of Magnetic Filter Metal Catchers

Filter magnets are available for a variety of purposes—oil filters, transmission fluid, and power steering filters along with transmission, engine, and drive axle sumps. You can place them anywhere you want protection. And this isn’t just about filter magnets, but any magnet you can place at the lowest point in a component to keep metal fragments away from moving parts. Automakers place magnets in automatic transmission sumps to catch harmful magnetic contaminants. You can place a magnet in your engine’s lowest point in the oil sump for protection.

Cruise the web and you will see all kinds of metal entrapment devices for both filtration and simple trapping at the lowest point in the oiling system. There are inline magnet filters for transmission and power steering cooler lines which are very effective. They don’t just trap debris, they catch ferrous metals that can do damage.

FilterMag isn’t just for engines, but also transmissions and rear ends. (Image/Jim Smart)

The most common name out there is FilterMag, which is available for virtually every application imaginable. FilterMag is a high-power magnet that “grabs” the outside of your oil filter—and any ferrous metal particles that happen to pass through it on the inside. Cut your oil filter open at the next oil change after installing FilterMag and you will see fine metal particles on the filter shell.

You will want to place FilterMag at the lowest spot on the oil filter, which keeps iron and steel debris well away from the oil pump. FilterMag also offers magnets for automatic transmission sumps, which are best placed toward the rear of the sump or at the lowest point to catch ferrous metals.

You can position these metal catchers anywhere on the transmission pan or case to capture harmful iron/steel particles. (Image/Jim Smart)

There is also MagnaFilter for engine oil filters and Magnefine for transmission and power steering fluid cooler lines. The Magnefine inline filters are installed in the return side (low pressure) side of the system to capture any debris on its way back to the pump. Magnafilters are installed between the oil filter and the engine’s oil filter mounting location. The magnetic disc structure of the Magnafilter provides for a regular replacement interval of 50,000 miles, which guarantees oil flow even under the harshest conditions without disrupting oil flow.

Magnefine does inline hydraulic fluid filtration and magnetic filtration for automatic transmissions and power steering. Position these filters on the return flow side (low pressure) only. (Image/Jim Smart)
Magnafilter does magnetic oil filtration inline with your engine’s oil filter. Life expectancy is 50,000 miles before you need to change it out. Screw it onto the oil filter flange, then, install the oil filter as shown. This is a magnetic disc filter that captures ferrous metals only. (Image/Jim Smart)

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Author: Jim Smart

Jim Smart is a veteran automotive journalist, technical editor, and historian with hundreds of how-to and feature articles to his credit. Jim's also an enthusiast, and has owned and restored many classic vehicles, including an impressive mix of vintage Ford Mustangs.