Oil filter: How it works, how often should you change it?

March 31, 2020
What does the oil filter do? An oil filter is the key component of the engine lubrication system. The engine oil is stored in the oil pan at the bottom of the engine.
4-cylinder engineOil filter in an engine.
When the engine is running, the oil pump draws the oil from the oil pan, and pumps it through the oil filter and then into oil passageways delivering it to various parts of the engine.

Over time, the oil absorbs abrasive metal particles produced as a result of mechanical wear, as well as pieces of carbon, sludge and dirt. The oil filter catches and stores these particles and other debris. The oil filter is typically made of a pleated paper material. In some cars, it comes built into a metal casing, like in this photo;
Oil filter Oil filter. Fig2.
in others, as a paper element or cartridge, called a "paper oil filter," see the photo below. An oil filter has a one-way valve that prevents the oil that is inside the lubrication system from draining into the oil pan when the engine is not running.

Does the oil filter need to be changed at every oil change? Yes, unless specified otherwise by the car manufacturer. The reason is that when the oil filter is dirty, it restricts the oil flow within the lubrication system. Good oil flow is essential for proper engine lubrication and longevity. An oil filter is not an expensive part ($10-$25) and, in most cars, it is easy to change.
What happens if the oil filter is not changed? Can it get clogged up? Yes, the oil filter absorbs and stores dirt, sludge and loose carbon particles that can eventually clog it up. An oil filter typically has a bypass valve that opens if the flow through the filter is severely restricted.
Paper oil filter The paper oil filter element or cartridge is installed inside the filter cap.
However, the oil that passes through the by-pass valve is not filtered and will contain abrasive metal particles and dirt. This will cause the engine to wear faster.

Does it matter which oil filter brand to use? An OEM (original) oil filter or a high-quality filter from a well-known reputable aftermarket brand is always a preferred choice. A poor-quality oil filter may not filter well or have other issues. For example, one of the common problems with poor-quality oil filters is when a one-way valve is leaking. This results in a lack of lubrication for a few seconds when the engine is first started. Is it really worth it to save a few bucks if a poor-quality filter can cause expensive engine problems?

Are oil filters specific for each car? Yes, each car requires a specific oil filter. Even different engines in the same car often require different oil filters. If in doubt, it's best to buy an OEM (original) oil filter from a dealer, where they can verify the part number by the VIN number of your vehicle. We know many people who buy OEM oil filters from a dealer and then supply it to the mechanic when taking a car for an oil change to an independent repair shop.

Does the new filter need to be filled with oil before installing? It's a good idea to fill the oil filter with oil when a brand new or a rebuilt engine is first started after the repairs or replacement, because the lubrication system is dry.
However, it's not necessary when doing a regular oil change, because the lubrication system still has some amount of oil in it. If in doubt, check the service manual for your car for proper oil filter replacement instructions. For example, the service manual for the 2009 Honda Accord instructs to inspect the old oil filter to make sure the seal is not stuck to the seating surface, then to "clean the seat on the oil filter base, then apply a light coat of new engine oil to the filter rubber seal". However, it doesn't say anything about filling the filter with oil. For many cars, you can find instructions on how to change the engine oil and the oil filter in the owner's manual.