Filter efficiency vs. effectiveness

CCI

Joined
Jul 15, 2009
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371
Location
New Mexico USA
As air filters go from brand new to slightly dirty they become somewhat less efficient in terms of possible total flow but they become more effective at filtering out the smaller particles. According to the service clinics I attended it's better to not change an air filter sooner than necessary.

Could oil filters work the same way? If an engine is relatively new, well maintained, not in severe service, good oil is being used, is there any case to be made for changing the filter every other oil change?
 
Oil filters typically get less efficient as they load up. Some are worse than others - it depends on how well the media is designed and it's ability to hold already captured particles as it loads up and the delta-p across the media increases. When the delta-p increases from loading up, it tries to dislodge already captured debris in the media, and as the debris dislodges it causes the downstream oil to become contaminated, that essentially decreases the filter's efficiency.

Read this thread from where the link pops into it - link below. The loss in efficiency is discussed with a few of the filters tested, and verifies what M+H/Purolator said a long time ago. It's an on-going misconception that oil filters become more efficient with loading ... that's not the case.

A filter with a higher ISO 4548-12 efficiency rating is most likely much better at retaining captured debris than the filter that has lower efficiency. The ISO efficiency test would certainly be effected if a filter was bad at retaining debris as the delta-p increased near the end of the test when the filter was loaded up pretty good.



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As the filter clogs would we see the lower sized end of particle count decrease yet over all have an increase of particles increase as the filter would open up the bypass more as the restriction increases ?
 
That is a good question, which I hadn't thought about. I had heard the same about air filters, but never thought about oil filters in the same way. I am glad the question was asked out in the open and will hope this question results in a discussion..
 
That is a good question, which I hadn't thought about. I had heard the same about air filters, but never thought about oil filters in the same way. I am glad the question was asked out in the open and will hope this question results in a discussion..
You mean for the nth time?

Hasn’t it already been answered in this thread as well?
 
As the filter clogs would we see the lower sized end of particle count decrease yet over all have an increase of particles increase as the filter would open up the bypass more as the restriction increases ?
The efficiency decrease under discussion happens before the bypass valve opens. It's the decrease in efficiency due to increasing delta-p across the media. That could also happen from any time there is a large increase in flow and resulting delta-p, like revving the engine to high RPM that would cause higher delta-p across the filter. IMO, this is another advantage of a higher vs lower efficiency oil filter. Filters that rate higher in the ISO efficiency test have better debris retention capability as delta-p increases.

And of course any time the bypass valve opens the downstream efficiency can be effected.
 
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