How Does An Oil Filter Work?

August 17, 2011  

As an essential component to any car’s engine, oil must be filtered efficiently to maintain its integrity. In the course of an engine’s operation, oil absorbs a number of contaminants:

  • Soot particles from combustion
  • Metallic particles from engine parts
  • Fungus from the air
  • Bacteria from the air
  • Dust and other dirt from the air

Your car engine’s oil must be filtered to remove organic and inorganic particulates so it can:

  • Help cool the engine through heat transfer
  • Seal gaps between piston rings and cylinder walls
  • Absorb contaminants
  • Suspend soot particulate
  • Suspend other organic particles (fungus, bacteria, dust) from the air
Filtering Oil

Oil, left unfiltered and/or unchanged, would eventually become saturated with particulates from combustion and from the air. These particles would wear down the components of the engine; especially the oil pump’s machined components and the bearing surfaces of the engine. The earliest engines burned poor quality oil, and as a result were changed often, eliminating the need for oil filtration.

The first oil “filters”, which were actually mesh screens installed to catch larger particulates, were not filters at all, and proved ineffective. Ernest Sweetland invented the first oil filter in the early 1920s, the Purolator:

Purolator = Pure + Oil + Later

It was not until the 1950s that oil filters were offered as standard equipment on automobiles. With improved oil chemistry and improved filter technology, intervals of at least 4,000 miles were achieved by the mid-1960s. Today, the “spin-on” oil filter is used universally in vehicles today.

Spin-On Filters

Even with technology that allows up to 10,000 mile intervals for oil changes, the filter’s job remain the same: clean the oil to to avoid engine damage. Construction of the spin-on filter is as follows:

  1. The filter is held to the engine block by a threaded central hole
  2. The external metal can is held against the engine’s mating surface with a sealing gasket
  3. The base plate is perforated just inside its gasket
  4. Filter material (usually synthetic) is inside the metal can
How Spin-On Filters Work
Once the filter is in place:
  1. Oil is pumped through the base holes into the filter by the oil pump
  2. Dirty oil is pushed through the filter media under pressure
  3. Clean oil passes back through the center hole to re-enter the engine
Over time, the oil filter will clog, in which case the bypass valve will open, allowing unfiltered oil to circulate through the engine.
Flow of Oil

Oil filters typically have two media types:

> Primary Media – captures particles down to 25 to 30 microns. As comparison, a human hair is 65 to 70 microns in diameter. A “full flow” filter has only primary filter media.

> Secondary Media – captures particles as small as 5 to 10 microns, which limits oil flow. Only a portion of the total oil (1% – 10%) is passed through the secondary media because it is so restrictive. The remaining oil is passed just through the primary media.

Magnets? Really?

Do not believe the filter manufacturers claims that installing magnets in oil filters to trap metals benefits. Claims have been made that:

  1. the magnetic forces act to stabilize oil molecules
  2. benefits are greater the longer magnetic field is applied to the filter
  3. fuel mileage is increased
  4. oil consumption is decreased
  5. emissions are decreased
  6. engine power is increased
Although magnets would remove some minute iron particulate and could attract ferrous metal particles, but in practice, the effect is minimal. Most metallic particulate in the engine are non-ferrous, or non-magnetic.  For an Everett Oil Change or Everett Tune Up Service, contact Carson Cars Auto Repair experts!