Oil filter: What is it for, and when is it important to replace it?

Oil filter
Publié le Traduit avec l'aide de l'IA à partir de notre article original (source :

An oil filter is a type of filter designed to remove impurities from engine oil. Oil filters are used in car engines, aircraft, and marine engines.

If we are talking about cars, this filter is located in the lower or middle part of the engine.

Table des matières

How does an oil filter work?

Oil filter

The oil filter removes dirt by forcing engine oil through a porous filter material. The first car engines did not use oil filters, which, together with the low quality of engine oil, caused excessive degradation of this oil, and therefore it was necessary to change it very often.

Nowadays, all automotive internal combustion engines are equipped with an oil filter. The basic components of an oil filter include:

Oil-filter cartridge, internal construction
  • Filter media: Made of paper, synthetic materials, or wire mesh, it catches dirt when oil flows through it.

  • Check valve: Prevents oil from flowing out of the filter when the engine is off, thus ensuring a constant supply of oil during starting.

  • Bypass Valve: Allows oil to bypass the filter if it becomes clogged, preventing engine damage due to lack of oil.

Types of oil filters

There are several types of oil filters, each of which has its own advantages and is suitable for specific types of engines:

Mechanical oil filters

Mechanical filters use a folded paper or fiber element to trap dirt. They are the most common type of oil filter and are usually more affordable. However, they have a limited filtering capacity and need to be replaced more often.

Cassette oil filters

Cassette filters have a more modern design with a reusable cover and replaceable filter elements. It is a more ecological alternative and provides a higher filtration capacity than mechanical filters.

Magnetic oil filters

Magnetic filters use a magnet or electromagnet to attract and remove metal particles from the oil. These filters are reusable and only require regular cleaning. However, they are not as effective at capturing non-metallic impurities.

Centrifugal oil filters

Centrifugal filters use rotary motion to separate contaminants from the oil based on density. These filters are more effective at capturing smaller particles but may require frequent maintenance.

Semi-flow oil filter

These filters work in such a way that part of the oil that goes to the lubrication system passes through the oil filter, and part flows directly to the lubrication points of the engine.

Nowadays, semi-flow oil filters are used only exceptionally because only half of the oil passes through the filtration, which causes insufficient engine oil cleaning.

Full-flow oil filter

These filters are very effective because all the engine oil passes through the filtration and thus captures most of the impurities. Thus, the lubrication system cleans all the oil during one flow.

Full-flow oil filters are made of filter paper and are designed as single-purpose, which means that they cannot be cleaned and can be changed completely with the casing or just the filter insert.

What is a replacement filter?

It is a filter insert and packaging, which together form one unit. When replaced, the entire filter changes. This type of filter is equipped with a safety valve that allows the oil to bypass the filter in the event that the filter element becomes clogged. This prevents the lubrication system from being disabled. The safety valve, therefore, has the same function as the reduction valve of the lubrication system.

This filter is also equipped with a breather valve that keeps the oil in the filter even after the engine is turned off, thus preventing the wear of the engine's moving parts due to the initial lack of oil. Without this valve, the oil would first have to fill the filter, and only then would it move to the engine's working parts.

Why should you not forget to change the oil filter?

Comparison of new and old motorcycle oil filters

Regular oil filter replacement is crucial for maintaining lifespan and engine performance. A clogged filter can cause:

  • Restricted oil flow leads to increased engine wear and potential damage.

  • High fuel consumption because the engine has to work more due to insufficient lubrication.

  • Higher emissions because dirty oil can contribute to the formation of sludge and carbon deposits.

Without an oil filter, impurities in the engine oil reach the engine's working parts, causing them to wear out faster. The oil filter should be changed at every engine oil change, as it is an essential part of the lubrication system.

Interesting facts about the oil filter

  1. The first cars did not have oil filters: The concept of oil filtration was not introduced until the 1920s. Previously, engines relied only on basic oil screens that offered limited filtering capabilities.

  2. Ernest Sweetland and George H. Greenhalgh invented the first full-flow oil filter in 1923. They patented the invention under the name Purolator. Purolator remains a well-known brand in the automotive industry today.

  3. Oil filters can significantly impact fuel consumption: A clean oil filter ensures optimal oil flow and reduces friction in the engine. The result is better fuel consumption and lower emissions.

  4. Synthetic oil filters are designed for extended use: Synthetic oil filters are made of synthetic materials such as fiberglass or polyester, providing improved filtering capabilities and longer life than conventional paper filters. They are especially suitable for vehicles using synthetic engine oil.

  5. Oil filter magnets can trap metal debris: Although not a standard feature, some oil filters are equipped with magnets that attract and trap metal particles in oils. This helps further reduce engine wear caused by abrasive metal debris.

Frequently asked questions about the oil filter

How often should I change the oil filter?

Replacing the oil filter at each oil change or as specified by the vehicle manufacturer is generally recommended.

Can a dirty oil filter cause low oil pressure?

Yes, a clogged oil filter can restrict oil flow, leading to low oil pressure and, in the worst-case scenario, potential engine damage. Changing the oil filter regularly can help maintain proper oil pressure.

Is it normal for oil to leak after changing the filter?

A small amount of residual oil may leak after changing the filter, but this should stop a few minutes after the engine is started. If the leaks persist, check that the filter is properly tightened and that the gasket fits properly.

Can I clean and reuse my old oil filter?

Some oil filters, such as magnetic or centrifugal, can be cleaned and reused. However, mechanical and cartridge filters have a limited filtering capacity and should be replaced according to the manufacturer's recommendations.


If you did not change the oil filter when changing the engine oil, you would be making a big mistake, because you would immediately spoil the new engine oil with dirt from the old oil filter. An oil filter is not an expensive part, so trying to save some money, in this case, just doesn't make sense.

Video instructions on how to change the oil filter: