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Why Is Changing an Oil Filter So Important?

A car oil filter.

We’ve long departed from the 3,000-mile oil change; most automakers now suggest longer oil change intervals, usually every 5,000, 7,500 or 10,000 miles. These longer intervals are possible thanks to both tighter engine-manufacturing tolerances and high-tech, low-viscosity engine oils, which make for more efficiency and better performance.

Changing an oil filter has always been recommended along with the oil change, yet some suggest that changing the filter less often could save money and time. What’s really going on here? Are oil filters just another money-making add-on or a critical part of every oil change?

How Engine Oil Filters Work

As suggested, oil filters filter oil. New, clean oil immediately starts to pick up metal flakes and old deposits from oil passageways. Over time, as the oil completes many thousands of circuits through the engine, it starts to oxidize, and other reactions generate particles in the oil.

Given that some passageways in your engine are exceptionally small — some main bearing clearances are just 0.002,” or slightly thicker than a human hair — you don’t want stray particles to get lodged in there. The oil filter captures these particulates and metal, preventing them from circulating through the engine and causing damage. But how much debris can the oil filter collect?

Unfortunately, that question isn’t an easy one to answer. Most filter companies express filter efficiency as a percentage of particles of a certain size that the filter is able to capture. However, few filters display this filter debris capacity, and some products don’t display any such information.

When Is the Right Time for Changing an Oil Filter?

Changing an Oil Filter is Best Done Before Dirty Oil Causes DamageAll oil filters have limited debris capacity and then become useless. Once an oil filter reaches capacity, excess pressure opens the bypass valve. This allows unfiltered oil into the engine lubrication system, where particles can wreak havoc on bearings, rings and journals, or get stuck in chain tensioners or lifters. Unfortunately, without some sort of mechanical clairvoyance, there’s no practical way to tell if the oil filter is stuffed. Changing an oil filter is the only way to prevent problems from occurring.

It’s a good idea to change an oil filter at the manufacturer’s recommended interval. Check your owner’s manual or maintenance manual for specifics. When in doubt choose the “severe service” service interval. Your vehicle may also have a built-in oil change interval light that comes on when it is time. Other vehicles has an “oil life percentage” notification that uses complex calculations to determine when your oil (and therefore your oil filter) should be changed.

In general, it’s better to be safe than sorry when it comes to oil filter capacity.

Check out all the filters available on NAPAonline. For more information on changing an oil filter, chat with a knowledgeable expert at your local NAPA Auto Parts store, or trust one of our 17,000 NAPA Auto Care centers for a complete oil change.

Photo courtesy of Wikimedia Commons.

Benjamin Jerew View All

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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