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What is an Oil Filter?

Katharine Swan
Katharine Swan

A car's oil filter is located on the side of the engine block, which is the lower, larger part of the engine. An oil pump circulates the oil through the engine. Every time the engine oil circulates, it passes through the filter, which protects the engine by catching any large particles in the oil that might damage the engine if allowed to circulate freely.

The oil filter serves a dual purpose, as it also protects the engine by retaining a small amount of oil when the car is turned off. The part that makes this retention possible is called the anti-drainback valve. While the engine is at rest, the oil drains into the bottom of the engine, leaving the moving parts at the top of the engine without proper lubrication when the car is started again. However, the small amount of oil remaining in the filter will circulate quickly into the top of the engine during the first couple of seconds after the car is started, restoring proper lubrication as soon as possible.

Oil filters should be changed when oil changes are performed.
Oil filters should be changed when oil changes are performed.

There are many different kinds of oil filters available. The standard version is usually sufficient, assuming it will be replaced within 3,000 miles (4,828 km). However, an important feature to look for is the anti-drainback valve; an oil filter that has this valve will retain oil while the car is off and provide valuable lubrication to the top of the engine during the first few seconds after startup, as described above.

When shopping for an oil filter, it is also important to avoid any fancy-sounding technology. An excellent example is the oil filter by a leading manufacturer that includes Teflon® in the filter itself; the Teflon® circulates through the engine with the oil. However, Teflon® is a semi-solid substance and has the ability to clog small oil passages within an engine. A filter with Teflon® in the filter material is not advisable, but one that uses Teflon® in the gasket should not have any adverse effects on an engine.

It is important to change your car's oil filter with the engine oil every 3,000 miles or three months, whichever comes first. Because the job of the oil filter is to trap large particles, preventing them from damaging the engine, it is safe to assume that after 3,000 miles it may well be getting clogged. A clogged filter will pose more resistance to the flow of engine oil, backing up the oil passages and preventing lubrication from reaching all parts of the engine. To prevent the serious damage that results from insufficient lubrication, it is imperative that you change your oil filter regularly.

Discussion Comments


@anon33881: You can use a standard car oil filter but it always better to use a 'marine grade' filter.


I would like to point out that not all oil filters are on the underside of the car. There are some cars with the oil filters under the hood of the car.


I have a boat with an inboard engine. The specs say it is a 350 (5.7L). Can I use a standard car oil filter or is a 'marine grade' filter needed?

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    • Oil filters should be changed when oil changes are performed.
      By: uwimages
      Oil filters should be changed when oil changes are performed.