Mazda Miata/B6 Oil Filter Study

Part I.

 A. Introduction

This study is probably long overdue, during my term as president of the Miata Club in 2002/2003, the displays of cutaway filters demonstrating the differences between fake and OEM parts at the parts counters of various auto dealers sparked my curiosity, and I toyed with the idea of engaging in a study of various Miata/B6 oil filters as a club project.  However, at the time I had yet to encounter any “fake” oil filters, at least not any that I knew to be patently bogus.  But just a few weeks ago (June 2005), two years after my initial interest on the project, I had gone to buy some parts for my car among the auto supply stores on Banawe St., in Quezon City, I took the opportunity to buy an oil filter, and to my surprise it was priced at only P90.  This surely must be a fake filter, so I thought.  But notwithstanding my initial assessment that this filter was a fake, I still bought it because it rekindled my curiosity as it could serve as a springboard to a complete study.  It got me wondering what the difference is between this inexpensive filter and the P300 to P400 varieties that can be bought from Allan Lavarro and Ramon Villacorta.  It was also at this time that Chito Frondoso as current president (’04-’05) also expressed his desire to embark on an inquiry as to the quality of these various filters.  Moreover, other members were also recommending another inexpensive filter, the made in Japan Vic filter which is priced at P150.  How do these inexpensive filters compare against the OEM filter?  Are their qualitative differences so great that we should give preference to the OEM filter?  Or are their differences so slight and miniscule that we can enjoy the discount yet still enjoy undiminished performance? Thus with the foregoing impetus, I felt that the time was indeed ripe to perform this study.

Before I go any further, please be reminded that I undertook this study on my own, using my own senses and forming opinions based on those observations as well as other independent studies that I’ve read on the matter.  Hence, some of the conclusions arrived at may have the taint of subjectivity.  However, as much as possible I’ve tried to provide you with photographs of the dissected filters and their components and described them in a manner that’s as objective as I can be, so you can make your own determinations and arrive at your own conclusions.

To continue: Three oil filters that are available in the Philippine market were collected:  the P90 Replacement “Mazda” filter; the P150 Vic filter; and the P350 to P420 OEM Mazda/Tokyo Roki filter.  The plan is to dissect the filters and subject their internal components to an inspection, measuring and comparing each against the others.

Update 23 July 2005:  Five more filters have been added to the test:  the Bosch filter which sells for P150;  the Ginza Japan filter which is available for P100;  The Power Long filter available for P150;  and upon the suggestion of Lowell Tortona, two filters specifically for the Honda Civic/Accord but which are also compatible for the B6 Miata, the made in Japan OEM Honda filter available for P330; and the made in Thailand replacement Honda filter available for P180.  The K&N filter was considered, however, its availability is extremely limited in the market and as such adversely affects its relevance to the general membership of the club.

Antecedent to commencing our comparison of the dissected oil filters, we first must learn how an oil filter works and what the components of an oil filter are inclusive of the functions of each of those components.  After we’ve learned how a filter operates and learned about its components and their functions, under this light, we will be better informed and we can then proceed to analyze the different filters that we’ve dissected from a learned perspective.  The following information regarding the engine lubrication of the B6 engine and the parts of an oil filter are not my analyses, but have been culled from other studies previously conducted and posted on the internet.

B. Primer:  How an Oil Filter Works and the Parts of an Oil Filter

How an Oil Filter Works:

Below is the engine lubrication diagram for the Mazda 1.6L/B6 engine. Note that as indicated above the oil pressure sending unit measures the pressure after the oil has passed through the filter (i.e. it reports the pressure at the inlet to the engine's oil galleries). Therefore filters with higher flow restrictions will reduce the pressure on the important side of things.

Oil comes in from the engine through the base of the filter through a series of 6 holes arranged around this metal base. The oil pressure presses on the anti-drain-back diaphragm and enters the filter can on the outer portion of the filter-element assembly, the oil then goes through the paper element and is filtered as it passes into the core of the filter-element assembly, from the core the filtered oil then enters back into the engine through the threaded mounting outlet hole at the center of the base of the filter.  If the element should get clogged and oil cannot pass through the filter element, the pressure builds within the can, once the pressure is high enough it pushes the spring on the by-pass valve at the other end of the filter, so oil can get into the core and into the engine.  However, there is no filtering medium through the by-pass valve, and any oil getting through the by-pass valve, into the core, and subsequently into the engine, is unfiltered and dirty oil.

The Parts of an Oil Filter

An oil filter generally consists of 6 discrete sections:

1. The Base, which contains the engine filter seal, mounting threads (outlet hole);
2. The Anti-Drain-Back Diaphragm is a one way valve which allows oil in to be filtered but doesn’t let it out through that valve.
3. The Can, which encloses the rest of the filter assembly and is roll mounted to the base.
4. The Filter, which contains the medium that removes foreign particles from the oil and is mounted on a sturdy frame.
5. The By-Pass Valve, which is rated for a certain amount of pressure so that it lets oil by-pass the filter when pressure exceeds OEM limits.
6. The Spring, which generally functions to ensure that the filter assembly fits snugly into the base and gasket.

The Base - This is the point of the filter which mounts to your engine. At its center is a threaded outlet hole.

Anti-Drain-Back Valve Diaphragm – In the interior of the filter assembly mounted to the base surrounding the outlet orifice is a flexible gasket that lies on top of a series of holes where the oil enters the assembly. The gasket acts as a type of one-way valve that only opens to let oil in through the holes to fill the assembly.  When oil pressure drops (engine is turned off, etc.) the gasket returns to cover the holes preventing the oil in the whole assembly from leaking into the engine and down into the oil pan. The gasket is generally called an anti-drain-back valve.

The Can - The can is the piece of metal that encases the entire assembly and is rolled into the base in order to create a liquid tight seal.  The shell and back-plate thickness are only relevant if your engine's oil system operates at unusually high pressures.  Occasionally, at such unusually high pressures, a seemingly strong filter can still leak due to a failure at the crimp between the can and back-plate.

The Filter-Element Assembly – This is generally a pleated piece of material wrapped around a frame that maintains its structural integrity (as oil flows from the outside to the inside and out the outlet hole). Usually the frame is made of metal, but can also be made of cardboard. The seam of the filter material is generally sealed with a strip of metal that clamps to two pieces together under high pressure. However, the seam can also be glued together. Lastly, most filter assemblies have a by-pass valve installed on their top, and a large hole at their base that fits into the gasket.

Probably the most important aspect here is the element surface area.  This helps determine the amount of filter media that is available to trap particles.  Cellulose media (basically paper) can trap fewer particles and can flow less oil per square inch because there are fewer passages through it.  Synthetic media has more passages and can trap more particles and flow more oil than cellulose per square inch.  For the same type of media, the smaller the area, the sooner the filter will become plugged and will end up bypassing much of the oil instead of filtering it.  Some filters use a cellulose/synthetic blend, so a direct comparison is not possible.  More pleats in the element do not necessarily mean more surface area (as you will soon see).  In fact, too many pleats can end up restricting the flow too much because there is not enough space between them to allow oil to flow.  Most of the cheaper filters use a mix that is mostly cellulose and/or cotton.  Some of the better filters use synthetics or synthetic blends.

The By-Pass Valve - This functions to prevent a clogged filter from rupturing. The valve functions to open during severe oil pressure spikes that happen during periods of very high engine speed. The by-pass valve also opens when the oil viscosity is too high (e.g. when the oil has thickened due to cold temperatures, or as a result of too long of an extended drain interval). For this reason, it is generally a really good idea to use the proper OEM specified multi-grade oil when using conventional motor oils in colder climates (i.e. 5w30 or 10w30 for the Prelude). If you use synthetic motor oil then this is not a concern at all as almost all brands pump at -40F.

There are a variety of designs for the by-pass valve. Generally, the valve uses a spring loaded design where oil pressure pushes the valve open as pressure builds up from a clogged filter. When a by-pass valve opens it circulates "dirty" oil directly back into the engine to ensure proper lubrication at all times. Usually, the valve is coated in some form of gasket material to prevent leakage.

The Spring – This is usually either of a leaf or a traditional coil design, and usually sits at the top of the can. Being placed at the top of the can causes the spring to push the filter snugly into the gasket at the base.

Part II

A. The Dissection:

All three filters were dissected using a metal hack saw to separate the shell from the base to reveal the internal components of the filters.

Update:  The five succeeding filters were opened up using a power grinder to cut the base of the filters off.

Here are exploded views of all 8 filters:

B.  Parts of the Filter

The Anti-Drain-Back Diaphragm:

In this component it is very difficult to articulate the differences in quality between the three without having each of them between your fingers and using the sense of touch to determine the qualitative thickness, substance and the subtle differences between the three.  Also, it is difficult to describe in words how each of them moves and reacts to pressure.  Nonetheless, at the next regular club meeting I’ll be bringing them and you can inspect them for yourself.  For now, you’ll just have to rely on my observations on these components.

Based on ocular and tactile analyses of all 8 items, it is clear that the design, construction and shape of the diaphragm for the Replacement filter are clearly inferior.  The diaphragm can even be made to remain at the open position with just a little bit of downward pressure on the filter assembly, if it does have that tendency when it’s mounted on the filter and on the engine it could easily allow dirty oil to flow back into the engine.

The rest of the filters seem to be generally equal when it comes to the quality of the anti-drain-back valve.

The Filter-Element Assembly:

Here are the filter element assemblies of all three makes side by side:

An inspection of the filter element assemblies reveals that most of the filters use what seems to be a paper medium folded with pleats, only a more in depth analysis can determine what they’re really made of.  The only filters that differed in filter mediums are the Honda OEM filter and the Power Long filter.

The Honda OEM filter seems to use a much higher quality medium made of a composite of paper and cotton.  Also, this Honda filter is the only one of the eight filters without a top and a base metal end cap, it is a very different design.  The Power Long filter is very different from the other filters as it uses a stainless-steel mesh filter medium.  According to the literature on its box, it is a “re-usable” filter.  However, I am positive that though this filter is far less restrictive to oil flow it most likely will not be able to filter as finely as the other filters with more traditional media. 

Measurements also revealed the following data.

 Filter Size:

“Mazda” Replacement filter measures 6cm in diameter and 4cm in height. 39 pleats.

The Vic filter measures 6.2cm in diameter and 4.7cm in height. 67 pleats.

The OEM Mazda filter measures 6.2cm in diameter and 4.55 cm in height. 54 pleats.

The Bosch filter measures 6cm in diameter and 4.4cm in height. 59 pleats.

The Ginza Japan filter measures 6cm in diameter and 4.4cm in height. 46 pleats.

The OEM Honda filter made in Japan measures 6cm in diameter and 5.3cm in height. 47 pleats.  This filter that looks like a paper/cotton blend, it looks much thicker than the others.

The Replacement Honda filter made in Thailand measures 5.6cm in diameter and 6.7cm in height. 40 pleats.

The Power Long filter made in Korea measures 5.1cm in diameter and 5cm in height.  This filter has no pleats since it’s made of stainless-steel mesh.

As you can plainly see from the picture above the Replacement filter is the smallest, followed by the Power Long filter, while the Vic, OEM, Bosch and Ginza are all almost similar in size, and the two Honda filters are the tallest in the bunch.

Pleat Spacing:

“Mazda” Replacement filter -  With only 39 pleats, the filter medium of the Replacement filter has pleats that are very irregularly and loosely spaced throughout the circumference of the filter, some of the pleats are spaced at .3cm while there are some spaced at over 1cm.

On the Vic filter, the pleats are more regularly spaced than that of the replacement filter.  Four pleats are spaced .1cm apart in one bunch, then that bunch will be spaced from the next bunch at .4cm, then the next four and so on and so forth.  As the pleated element goes around, the clearance in between pleats become more loosely spaced, ending in spaces of .3cm within the bunch of four, with a .5cm space between bunches. 

The spacing between pleats of the element on the OEM filter is the most consistent amongst all three.  All around, the pleats are spaced between .3cm to .55cm from each other, sufficiently spaced to allow oil to pass through yet tight enough to maximize the number of pleats, hence, maximized surface area.

A perfunctory inspection may lead one to believe that the Vic filter would be the best in this aspect since it has the tightest spacing between pleats and hence, it should be have a longer filter medium and should consequently also have the greatest filter area.  However, more pleats in the element do not necessarily mean more surface area.  In fact, too many pleats tightly spaced can end up restricting the flow of oil through those tightly spaced pleats because of insufficient space between the pleats for oil to flow.

The Bosch filter had even tighter pleat spacing and more pleats than the OEM Mazda filter.  However, as its picture demonstrates, there was a lot of haphazardly slapped on glue in some portions of the filter.

The Ginza Japan filter was a bit better than the Replacement “Mazda” filter, it had more pleats and it was bit more regularly spaced and also its size was rather similar if not a bit smaller than the OEM Mazda filter.

Although, the two Honda filters were outwardly larger than the OEM Mazda filter, and the filter elements do seem taller, measurements will reveal that they’re also smaller in diameter compared with the OEM Mazda filter and that they also have less pleats.  I surmise that if their filter media were spread open, the Honda filters wouldn’t have any more filter media than the OEM Mazda filter.

The Power Long filter is by far the most different from all these filters, because of its stainless steel mesh filter medium.  Judging by appearances only, I doubt if this filter would be able to filter as much dirt as the paper or the paper/cotton blend media that other filters in this test have.  However, this filter is also reusable.  We would need to subject the various filter media for tests on filtering ability.

The By-Pass Valve:

The by-pass valve on both the Replacement filter, the Vic filter, the Bosch filter, the Ginza Japan filter, Power long filter, and both Honda filters were all very similar in design.  They both have one .8cm hole for the by-passing oil to pass through at the top of the filter-element assembly with a spring loaded valve.  The Bosch filter however, has a rubber gasket seal on its top which is the only filter to have such a rubber gasket on its by-pass valve.  The OEM Honda filter has the distinction of having its by-pass valve mounted on the can spring and not on the top end cap.  However, despite the mounting distinction, the design of this by-pass valve is very similar to the rest.   The spring activated valves for all 7 filters had similar levels of resistance.

The OEM by-pass valve was very different from the others.  This one had 7 holes arranged in a circle, each hole measuring .4cm for the by-passing oil to pass through.  The spring activated valve on the OEM filter had a much higher level of resistance compared with all the rest of the filters.  

The Can: 

According to the man that wielded the hack saw to open up the filters, the metal used for the OEM filter was far more difficult to saw through compared with those on the Vic filter and the Replacement filter, both of which required a lower effort to saw through.

I cannot report on how difficult it was to open up the fiver filters that followed inasmuch as a power grinder was used to open them and it cannot be determined if any of these cans offered a higher resistance compared with the others.

Part III. Conclusion: 

A cursory inspection of each of the filters’ exterior and their packaging will prove that it’s not very easy to distinguish the differences between the eight variants that were the subject of this study.  In fact, an ordinary user might even assume that all eight filters would work just as well as any of them since they’re all encased in a painted metal can with holes in the bottom and come in a printed box, but nothing can be further from the truth.  As demonstrated above, there are differences in quality and construction between some of the subjects.

In this comparative study, the OEM filter is the standard we’re using to judge the other seven filters.  Based on this standard, the quality of the Replacement filter is patently and grossly inferior, the next most inferior is the Ginza Japan filter.  The anti-drain-back diaphragm on the Replacement filter is of very poor quality, so poor that it might even allow unfiltered oil back into the engine the same way it came in.  Hence, at the very first stage of a filter’s function, the inferior quality of the anti-drain-back diaphragm on the Replacement filter has already given an indication of how poorly it will perform.  Moreover, its poorly assembled filter media as demonstrated by the loosely and highly irregular pleat spacing indicates that it contains far less filter media compared with that on the OEM as well as that of the Vic filter.  Because the Replacement filter and the Ginza Japan contain less filter media they consequently must have a diminished ability to filter dirty oil.  And finally, under conditions where the by-pass valve will come into play, its by-pass valve has only one .8cm hole for the oil to pass, and the spring on its valve has a resistance that’s nowhere near as stiff as that on the OEM valve.

In the area of the filter medium, the best was that of the OEM Honda filter which seemed to be of paper/cotton blend.  The worst was that of the Replacement “Mazda” and the Ginza Japan filter both of which had very irregular pleat spacing and a smaller filter area than the standard.  The Power Long filter was the most unusual being made of stainless steel mesh.  It would be much better to subject the different filter media to a genuine test to see which filters the best.

I had hoped that one of the lower priced filters would come close to the quality of the construction and materials of the OEM filter, but neither of them can even approximate it. The Replacement filter fails with the inferior quality of its anti-drain-back diaphragm, the poor construction of its filter-element-assembly, the grossly insufficient filter medium, and the inferior design of its by-pass valve; the Ginza Japan filter is not much better than the Replacement “Mazda” filter; the Vic filter meanwhile surpasses the Replacement “Mazda” filter only in the area of the anti-drain-back diaphragm.  The Vic variant’s filter-element-assembly cannot be considered to have the same quality as that of the OEM filter because of the inadequate attention given to the spacing of the pleats of the filter element, which as we’ve learned may have ramifications on oil flow.  Finally, the by-pass valve on the Vic filter has the same inferior quality as that of the Replacement filter; the Bosch filter’s filter medium is a bit smaller than that of the OEM filter and that of the Vic filter, however it’s pleat spacing is regular and not as closely packed together thus allowing a smooth flow of oil, however, there was excess glue spattered in some of areas of the filter which made appear of low quality.  Nonetheless, it remains to be seen how this excess glue can affect performance.  The two Honda filters were of acceptable quality with the OEM Honda filter medium having even better quality than that of the Mazda OEM filter.  The quality of the Power Long filter is also acceptable, however, a determination cannot be made as to the filtering ability of the stainless steel mesh medium without testing.

Where the difference lies between all these filters when compared with the OEM Mazda filter is the by-pass valve.  The by-pass valve on the OEM Mazda filter requires much greater pressure compared with all the other filters.  Also, the OEM Mazda filter has the only by-pass valve with several holes arranged in a circle compared with all the rest of the filters which only have one small .8cm hole.

Notwithstanding the foregoing, this study, however, merely delved into the quality of the construction and the materials of the Replacement “Mazda” filter, the Vic filter, the Ginza Japan filter, the Bosch filter, the Honda OEM filter, the Honda replacement filter and the Power Long filter in comparison with that of the OEM filter.  Although performance data may not be far behind, the conclusions based on quality is still a totally different matter compared with data and conclusions based on performance, which can only be determined by tests on oil flow, filtering abilities as well as the pressure at which the by-pass valve activates. 

I hope that you all have learned from this exercise as much as I have.  In any case, we will no longer be wondering what’s in those filters and if any of them are just as good as the OEM filters in terms of quality.

Joey Bernardez
Manila, Philippines
24 August 2005 

Acknowledgements:

• Thanks to Allan Lavarro who provided the OEM Mazda/Tokyo Roki filter, free of charge.  Allan sells this filter at his shop for P350;
• Thanks to Jojo Ozaeta who generously provided the Vic filter from his supply of spares;
• Thanks to Ramon Villacorta and CarShack for providing the Bosch filter, the Ginza Japan filter and the Power Long filter, all  free of charge as well as for opening the said filters.

ANNEX “A”

Oil Change Intervals

Oversized filters offer you the chance to use extended drain intervals with your motor oil.

Honda recommends that you change the oil in your Prelude every 7500 miles. Many dealers attempt to get you change the oil in your car every 3000 miles. Changing your oil every 3000 miles is basically a complete waste of your money, and bad for the environment. (That used oil needs to go somewhere...)

Even the worst of oil filters will last for 3000 miles without any problems at all, and almost any motor oil will last for 7500 miles.

If you use Redline, Mobil 1, AMSOIL, Royal Purple, or Valvoline synthetic motor oils you can easily run your oil in your engine without any problems for the OEM recommended change interval of 7500 miles.

The only time you have to consider changing your motor oil at shorter intervals is if your car is not a daily driver, and will not warm up to full operating temperature for at least 30 minutes a day. The reason for this is that small amounts of moisture (water) in the air tend to soak slowly into your motor oil. (The oil system is not truly closed, even though you have an oil cap.) The water mixes with the oil and other matter in the oil system and forms acids that can eat your engine parts over time. Warming up the engine causes the moisture to leave the motor oil. If you are changing your oil every 3000 miles (because you drive the car once a week) or at a specific time intervals (every 4-6 months because you aren't putting 3000 miles on the oil), then it's not as import to use synthetic motor oil.

Some people will disagree with the above, but the fact is that just about every brand name non-synthetic oil (or "dino") will last 3000 miles and have almost no significant wear to the oil or engine. It is not cost effective to use synthetic oil if you car sits for long intervals with low mileage.

The chief advantages to using synthetic motor oils are typically considered to be better at extended drain intervals, have better thermal stability, better cold flow characteristics, superior additive packages, and a lower coefficient of friction (resulting in lower engine wear and better gas mileage).

Taken from the North Texas Prelude Owners Website

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