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Filtering the flow

October 11, 2010
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Oil is the lifeblood of an engine. It lubricates, cools, seals, absorbs contaminants and suspends soot and wear particles before they can do damage.

Think of the oil filter as the kidney; filtering blood and keeping harmful dirt and contaminants from penetrating and gumming up the inner organs.

And just as kidney failure in humans spells serious illness, oil filter neglect can lead to excessive engine wear and even premature engine failure.

How does the oil filter work?
Oil from the oil sump (pan) is pumped through holes on the perimeter of the oil filter base plate.

As the oil passes through the filter, the filter media (which can be made from various types of materials ranging from paper to cellulose fibers), traps contaminants be-fore they can move on to the engine.

The oil then flows to the center tube and back into the engine through a hollow, threaded center-mounting stud.

Today, there are primarily two types of engine-oil filters in common use:

1) Spin-on: Spin-on oil filters are enclosed in a steel case with a threaded bottom assembly. As the name implies, these filters directly spin onto a threaded stud at the engine’s oil-filter adaptor.

Spin-on oil filters are often side-mounted and can be mounted at inverted angles. They are most commonly designed into North American automobiles.

2) Cartridge: Cartridge oil filters generally perform the same function as spin-on oil filters. The main difference is that a removable lid/cap provides access to the filter media inside a fixed canister or housing unit.

Cartridge oil filters are predominately used by European vehicle manufacturers, such as BMW, Mercedes-Benz and Volkswagen, although some North American manufacturers have started to use them.

Performance measures
When stocking replacement oil filters, it is important to understand how their performance is measured and tested. Oil filter performance is evaluated using five criteria:

  • Efficiency — Efficiency is the percentage of contaminants that are actually caught and withheld from the oil as it passes through the filter.
  • Capacity — Capacity is the amount of contaminants a filter can remove and hold before it becomes too restrictive to oil flow.
  • Flow restriction — Flow restriction is the resistance to flow of the oil being filtered through the media.
  • Life — Life refers to the actual number of test hours (under lab conditions) during which a filter can be used before the media becomes too restricted to flow.
  • Micron rating — Micron rating is the size of the particles that the filter media will effectively trap.

Most quality oil filters are performance tested in two ways — either through a single-pass efficiency (SPE) test or a multiple-pass efficiency (MPE) test.

The SPE test determines a filter’s ability to remove contaminants on a single pass through the oil-filter assembly. This test provides a measure of overall particle retention, but does not simulate real-life driving conditions.

The MPE test uses repeated passes until failure. Testing under these conditions best simulates how a customer actually drives.

Filters that are tested using these methods provide better — though not necessarily 100 percent — insurance that the filter will perform properly to OEM performance requirements in real-world conditions.

A filter meeting these and other test requirements provides better warranty protection in the event of a filter concern.

Maintenance service intervals
When and why do oil filters need to be changed?

As oil filters become too restricted due to build-up of contaminants, they begin to negatively impact oil pressure and flow. Over time, clogged oil filters can restrict the flow of oil to the engine.

As the filter media degrades, it can begin bypassing oil contaminants that are suspended in the oil. Continuous recirculation of contaminants throughout the engine can lead to premature wear and costly engine damage.

There are several opinions about when to change the oil filter. Many facilities provide a full oil-change service, which includes engine-oil exchange and oil filter replacement.

Because manufacturers’ recommendations for oil filter changes vary widely, the safest way to determine when to change an oil filter is to follow OEM recommendations for the particular vehicle depending on the driving conditions in which it is operated.

Defensive driving
Driving condition definitions can vary by OEM, but in general they are categorized as normal/highway or severe/city.

Some severe driving conditions listed by most OEMs include, but are not limited to:

  • Frequent short trips (less than 10 miles);
  • Frequent driving in city traffic;
  • Frequent driving in extreme hot or cold temperatures;
  • Frequent driving on dirt or gravel roads or mountainous or hilly terrain;
  • Towing; and
  • Long idling periods.

In these instances, most vehicle manufacturers recommend engine oil and filter services on an accelerated schedule.

Oil filters may not get as much attention as the motor oil itself, but they play a critical role in protecting vehicle engines from wear and damage.

Changing the oil and oil filter as recommended by the OEM is a small price for drivers to pay to help keep their engines running more efficiently and longer.


Ricky Jackson is national technical service advisor for Jiffy Lube International, Inc., a subsidiary of Shell Oil Company. Ricky provides technical support to a fast lube network of more than 2,200 service centers and has more than 17 years of automotive experience as a Ford ASSET graduate/technician. He is also a member of Automotive Maintenance Repair Association and the Motorist Assurance Program.

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