Oil Filters Revealed

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This page contains my *personal* slant on oil filters.  It is largely based on the things I discovered in the Oil Filters Revealed article.  Since there was concern about the influence of some of the subjective information on that page, it has been removed and put into this page.  Again, these are my personal opinions and I am just a concerned automotive enthusiast that is tired of being misled by branding tricks.  In reality, I am an Electrical Engineer with no qualifications in the area of filtration analysis.  However, I have eyes and some common sense, which has proven to be enough to accomplish what I set out to do.

What Makes A Good Filter?

Engine oil filters have one purpose in life: to filter out the particles that enter the oil so that they don't act as abrasives when the oil recirculates.  The filter is a cellulose (paper) or synthetic media that is usually contained in a steel can.  The front of the can typically has a threaded center with surrounding holes.  Oil enters through the surrounding holes, passes through the filter media, and exits through the threaded center.  The filters usually screw right onto the engine block using an o-ring gasket to prevent leakage.  Many filters have an anti-drainback valve to prevent dirty oil from draining back into the oil pan through the oil pump.  They also have a pressure relief or bypass valve that will allow oil to bypass the filter element in the event that it becomes too plugged to pass enough oil.  This prevents engine oil starvation and the possibility of destroying the element, possibly causing pieces of it and the junk it filtered to enter the engine.  Also, when the oil is cold and very thick, it will tend to bypass the filter through the pressure relief valve because it cannot pass through the element until it thins out somewhat.  If it did not do this, the filter element media would collapse and tear open.

A good filter has a strong steel can to withstand the high oil pressure (60-80psi when cold), an anti-drainback valve that actually works without creating too much back pressure, a pressure relief valve that doesn't leak, and a strong element and cap that can with stand the pressure and flow of oil without falling apart.  The element media has to be able to trap small particles, but without restricting the flow too much.  Cellulose (paper) media is used on economy filters and works OK.  The fibers in the paper acts as a mesh to block particles down to a certain average size, while allowing the oil to pass through.  Some manufacturers add other media, such as cotton, to the cellulose to improve its performance.  There is synthetic fiber media for the high-end filters that has smaller passages to trap smaller particles, but can pass more fluid through it because it has more of them.  There is also media that is a blend of these two.  There are also "depth" filters that are usually made of synthetic material that has a passage size gradient to it.  In other words, the deeper into the element the oil goes, the smaller the passages get.  This way, large particles are trapped in a different spot than small particles, which allows the filter to hold more particles before it "blocks" (becomes too restrictive).

All filters have to undergo SAE (Society of Automotive Engineers) tests to prove that they meet the engine manufacturer's requirements.  The SAE J806 test uses a single-pass test, checking for contaminant holding capacity,size of contaminant particles trapped, and ability to maintain clean oil.  As an amendment of the J806 test, the multi-pass test also looks for filter life in hours, contaminant capacity in grams, and efficiency based on weight.  The efficiency of the filter is determined only by weight through gravimetric measurement of the filtered test liquid.  Typical numbers for paper filter elements are 85% (single pass) and 80% (multi-pass).  A new test, the SAE J1858, provides both particle counting and gravimetric measurement to measure filter capacity and efficiency.  Actual counts of contaminant particles by size are obtained every 10 minutes, both upstream (before the filter) and downstream (after the filter), for evaluation. From this data filtration ratio and efficiency for each contaminant particle size can be determined as well as dust capacity and pressure loss as a function of time.  Typical numbers for paper element filters are 40% at 10 microns, 60% at 20 microns, 93% at 30 microns, and 97% at 40 microns.

Recommended Filters

Based on the simple criteria above and the information I gathered in the Oil Filters Revealed, I have found some filters that are readily available and are of good quality in my opinion.  I have disassembled many filters and made observations and measurements on them.  Sadly, some of the most common and popular filters don't cut it in my book.  Those filters are described in the next section.  The filter names are also links to the reference filter page, which gives the intimate details of that filter in the Chrysler/Ford reference filter version.  You will find all the hard data for these filters there.  What follows are filters that I recommend in alphabetical order:


The SuperDuty line of filters is no longer being sold by AMSOIL.  They now have their "Absolute Efficiency" line of filters that are intended for long duration use along with their premium synthetic oils.  The SuperDuty filters had to be changed out at least once between oil changes.  From the pictures, they appear to be manufactured by Donaldson.  Donaldson manufactures filters mainly for truck applications intended for long duration use.  They also manufactured the Hard Driver filter, which I used with great success for several years.


These filters are well constructed and are highly regarded in trucking circles.  They don't have as much surface area as some others, but they are one of the best filters you can get for around $5.  These are the filters I have been using lately.


This used to be another Champion Labs filter sold at Auto Zone, but now it is made by Purolator.  It has an impressive surface area and uses a cellulose/synthetic blend media.  This should result in well-above average holding capacity.  I generally like the Purolator design as well, so I wouldn't hesitate using a Bosch after verifying it was still a Purolator.


Like NAPA, they sell two lines of oil filters.  One is painted red and the other is painted blue.  They are both made by Dana/WIX and the blue one is supposed to be better.

Fram Tough Guard

Even with all the problems of the other Fram filters, this one is not too bad.  It has a heavier filter element with more surface area, a silicone anti-drainback valve, the cheap pressure relief valve, but with an integral screen to keep out large particles, and enough inlet holes for good flow.  The only other drawback to this filter is that it is capped on each end with cardboard instead of metal.  Looking in through the center outlet does not reveal any paper end caps, but they are there.  I personally do not use this filter, but the design didn't have enough bad qualities to cause me to tell others to avoid it.

Hard Driver

This was one of the few oil filters that uses a fully-synthetic filter element with a dual-density layering "depth" media.  The construction of the filter is what you would expect from a quality filter with steel filter element caps and special epoxy-coated steel mesh retainers to keep the element from flexing.  It also has a good flowing, strong steel case and a zinc-coated backplate to prevent preinstallation corrosion.  I used these for a few years with no problems until Donaldson stopped manufacturing them.  Donaldson does list part number P169071 in their Endurance line for the same application.  This may be a viable substitute for the Hard Driver.


It's a white Mobil 1 filter with a nut welded to the back.  It's made by Champion Labs using what I call their "performance" design instead of the "Ecore".  Save the $2-$3 plus shipping and get the Mobil 1.

Mobil 1

This filter is made by Champion Labs using what I call their "performance" design instead of the "Ecore".  It uses a synthetic fiber element that can filter out very small particles and has a high holding capacity.  It is rated by the manufacturer at just under the Purolator Pure One as far as filtering capability, but is still very much above conventional paper filters.  It also has a very strong construction to withstand high pressure spikes during start-up.  Given the choice between the Purolator Pure One and the Mobil 1 filters, I would choose the Mobil 1 because of the restriction concerns of the Pure One.  However, as with all Mobil 1 products, expect to pay 2 - 3 times as much for this filter.  I have seen this filter sold at Auto Zone and K-mart and used them a few times, but I feel they are not worth the money in the end.

Though I have never had problems, I had received feedback from a few people back in 1999/2000 that these filters may leak at the base.  It seems that the seal between the backplate and can may burst under high pressure (at startup).   These were on Ford engine applications.


The one I opened in 1999 seemed to be a Purolator hybrid.  It had the Premium Plus case (anti-drainback valve, gasket, etc), but with what appeared to be a Pure One filter element.  This was a cheap way to get a Purolator Pure One.  It is sold at many locations including Auto Zone, Pep Boys, etc.  I have heard from several people that Motorcraft seems to switch between Purolator and Champion Labs as the manufacturer so be observant.  The Motorcraft I took apart in 2008 appeared to be a regular Purolator Premium Plus.  Not worth the extra couple of bucks anymore in my opinion, but it probably looks snazzy under a Ford hood.


They sell two lines of oil filters: NAPA Silver and NAPA Gold.  They are both made by Dana/WIX and there is no obvious difference between them.  They may have different elements, but NAPA does not state that this is the case.


This is a Purolator Premium Plus that I have seen at Murray's Auto Supplies.


This is a Purolator Premium Plus that I have seen at Pep Boys.  Pep Boys also sells the Purolator Premium Plus brand, which is pretty dumb (to be selling both).

Purolator Premium Plus

The Purolator is a solid design.  It seems to have one of the tougher paper filter elements of the low-end filters and the bypass valve is built right into the cartridge.  There are no internal sealing problems with this filter at all.  There is an assembly string that is wrapped around the filter element, probably to hold it in place while the glue cures in the end caps.  In the ProLine (one of the Purolator clones), the string was wrapped too tightly and had damaged the filter element.  All the other Purolator-made filters (8 in all) had no trouble, and even the damaged one would probably have been fine.  I usually go with these in a pinch or when recommending the cheapest oil filter possible.

Purolator Pure One

This is an interesting filter design made by Purolator.  Most of the construction of the Pure One is the same as the Purolator Premium Plus.  The big difference is the filter element itself.  It has a dense paper/fiber filter element that can filter very small particles.  The result of this is cleaner oil exiting the element, but more oil restriction.  Purolator addressed this by adding more filter material (more and deeper pleats).  After seeing one of these filters cut open, I am apprehensive about this filter.  It seems to have so many pleats that it is almost a solid chunk of filter element.  It seems like it would end up restricting the flow, more than anything.  Purolator has plenty of data on the filtration abilities of this filter and I don't doubt it, but they have no flow data.  Even so, I don't see any major problems with this filter.  It also sports a silicone anti-drainback valve and a PTFE treated nitrile rubber gasket.


Another quality oil filter similar in design to the Purolator.  It has metal end caps on the filter element, a standard nitrile anti-drainback valve, and a seemingly good flow.  They are manufactured by the Dana corporation.  These appear to have a depth gradient filter element, which uses cotton fibers to progressively trap smaller particles as they get deeper in the filter.  This helps maintain good flow as the filter gets plugged.

Filters To Avoid

The following list of filters have known problems.  You will see well-known names here and will probably be disappointed.  This is because many of these brands have stopped making their own filters and buy from a common manufacturer.

AC Delco Duraguard

AC Delco no longer seems to manufacture oil filters.  They are now made by Champion Labs using their new "Ecore" design.  See that section below for the details.

Champ (Ecore)

Champion Labs touts their new "Ecore" design as a major advancement in oil filter technology.  In my humble opinion, they are a major advancement in cost savings for Champion.  I have no data to back this up, but that's what fiber end caps and plastic core tubes say to me.  I particularly don't like their "patent pending" bypass valve design, which depends on the stamped leaf spring at the back of the filter to regulate the bypass pressure.  One unlucky dent in the back of the can knocks it out of whack, assuming it was correct to begin with.

Fram Extra Guard

Years ago Fram was a quality filter manufacturer.  Now their standard filter (the radioactive-orange cans) is one of the worst out there.  It features cardboard end caps for the filter element that are glued in place.  The rubber anti-drainback valve seals against the cardboard and frequently leaks, causing dirty oil to drain back into the pan.  The bypass valves are plastic and are sometimes not molded correctly, which allows them to leak all the time.  The stamped-metal threaded end is weakly constructed and it has smaller and fewer oil inlet holes, which may restrict flow.  I had one of these filters fail in my previous car.  The filter element collapsed and bits of filter and glue were circulating through my system.  The oil passage to the head became blocked and the head got so hot from oil starvation that it actually melted the vacuum lines connected to it as well as the wires near it.

Fram Double Guard

Another bad filter idea brought to you by your friends at Fram.  The filter itself is a slightly improved design over the Fram Extra Guard, but still uses the same filter element.  It has a silicone anti-drainback valve, a quality pressure relief valve, and enough inlet holes for good flow.  The big problem is that they are trying to cash in on the Slick 50 craze.  They impregnate the filter element with bits of Teflon like that found in Slick 50.  As with Slick 50, Teflon is a solid and does not belong in an engine.  It cannot get into the parts of the engine that oil can and therefore does nothing.  Also, as the filter gets dirty, it ends up filtering the Teflon right out.  DuPont (the manufacturer of Teflon) does not recommend Teflon for use in internal combustion engines.  Please do not waste your money on this filter.

Fram High Mileage

Yet another bad filter idea brought to you by your friends at Fram!  Gotta love these guys.  It's a Fram Extra Guard with a weird goo cartridge suspended on the clean side of the filter, blocking the outlet.  It's supposed to be some kind of additive package, but if you want a high mileage oil, buy a high mileage oil.  I don't trust these guys...sorry.


This filter is a Fram.  It is the exact same design as the Fram Extra Guard filter and it is junk.  On the up side, it costs $1 less than the Fram version.

Quaker State

This is another Fram Extra Guard that I have seen at K-mart.  It used to be a Purolator, but Quaker State is now owned/controlled by Pennzoil...


This is a Champion Labs "Ecore" filter that I have seen at Auto Zone and Walmart.

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Updated 01/25/2008.

Copyright © 1996-2008 Russ W. Knize.