What’s in an oil filter, and how does it work? (Pt. 1)

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Cutaway of an automotive oil filter

A cutaway image of an automotive oil filter. (Photo Credit: Public Domain/Harrikkamies/Wikipedia)

You know that your car’s engine needs clean motor oil to function properly. It helps transfer engine heat; seals gaps between piston rings and cylinder walls; and soaks up system contaminants and soot from the combustion process that can gum up an engine. If oil is left to sit for too long, it becomes saturated with these byproducts and begins to wear down engine components, which is where the oil filter comes in. First introduced in the 1920s by Ernest Sweetland and standard in canister form by the 1950s, oil filter technology removes contaminants from the motor oil and extends the necessary duration between oil changes, to the point where by the mid-1960s, 4,000-plus miles between changes with a spin-on filter system was possible. Today’s clean-running engines can go as much as 10,000 miles between changes with modern filters. What’s in an oil filter, and how have they become so much more efficient?

How does the oil filter work?

Today’s spin-on oil filter is literally a metal can with a sealing gasket that enables the filter to sit flush against the engine’s surface. The base of the can holds a gasket in place, and that base place is perforated with holes around the area inside of the gasket. There is a threaded central hole where the the filter screws into the engine block. Synthetic fiber filtering material is found inside the can. The oil pump within a car’s engine sends oil to the filter, where the filtering material takes out as many impurities from the oil as possible, then sends the cleaner oil back into the engine. Particles as small as 5 microns can be filtered out of the oil (secondary media), but the most commonly caught contaminants are 25 to 30 microns in size (about half the thickness of a common human hair). Not all oil filters have a secondary media filtering ability.

The longer the oil filter on a car is, the more particles that can be suspended as part of the filtering process. Once the filter becomes overloaded with debris, however, oil can no longer flow through cleanly, causing the cycles fluid to become dirty and ineffective. The engine’s bypass valve then takes over to ensure oil gets back to the engine, but no filtration occurs at that point, which can be very damaging to the engine.

Oil filter hates magnet

Some oil filter manufacturers actually encourage consumers to put magnets inside their oil filters in order to trap additional metal shavings from the oil. They claim that this somehow “stabilizes” the oil molecules and increases fuel efficiency and engine power while decreasing emissions. Not only is none of this true, but some of the claims are impossible to achieve. Removing sub-micron sized iron particles from motor oil is possible, but there is no true measurable effect on engine performance. Most of the metallic particles in the oil come from bearing materials, and as such, they aren’t ferrous in nature. Magnets won’t attract those materials.

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What kind of oil filter do you need?

You can go cheap or you can go reasonable when it comes to an oil filter for your car’s engine. When you go cheap, you get what you pay for, as a $2 filter will do next to nothing to ensure maximum engine efficiency. A cheap filter can work, and it may have a warranty like a more expensive model, but the likelihood of lessened performance is greater. Don’t go generic. Look at the gasket quality, because that’s where leaks will occur if the filter is bad. You want materials that won’t become hard and brittle too quickly. Consult with your car’s owner’s manual and a reputable mechanic if you aren’t sure. A name-brand oil filter for $10, or one with dual stage filters for just a bit more, is a good idea.

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Looking at a FRAM oil filter


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