Mildren Automotive


Engine Oil Filters cut open to reveal the Best Rotary Engine Oil Filter

DPP_1758I am sure all engine oils do a good job of lubricating your engine and maintaining oil pressure under most driving conditions at least for the first short period of use. The better quality oils have the ability to a good job for longer and they generally do it better. That is unless you use a second rate oil filter.


The effect of using a poor quality filter is its;

  • Poor ability to filter particles and contaminants out from the oil. The same contaminants responsible for engine wear. Moving parts rely on oil to separate two bearing or sliding surfaces wanting to touch.
  • Limited ability to store large amounts of unwanted particles. Poorer quality filters may have a limited amount of filter media and therefore become restrictive or blocked before your next oil change.
  • Ability to flow high volume of oil to the engine. Poor quality filters will be restrictive to flow, therefore causing a pressure drop across the filter, reducing much needed oil pressure to the engine. Rotary Engines operate on much higher oil pressure than reciprocating engines, therefore any compromise to oil pressure or flow is certainly unwanted.

I decided to take a closer look at the filters I have been recently recommending and selling  as well as consider a new filter produced by Mazda, imported from Japan.

Australian Motors Mazda were kind enough to donate me 2 of their best filters recommended for Mazda Rotary engines to cut open.  Wix Filters were also kind enough to donate a filter to cut open for comparison.



Mazda Engine Oil Filters, Japanese imported filter  LHS and Australian made filter RHS


WIX Engine Oil Filter LHS and Mazda Australian made Engine Oil Filter RHS

The first Mazda oil filter I looked at was an Australian made Mazda filter.  The filter I have been using on almost every rotary engine I have built since year 2000.  Made in Australia and commonly stocked by all Mazda Dealerships.

The second Mazda oil filter was imported from Japan and an oil filter new to me.  Slightly larger, but will still fit on every Mazda Rotary engine.  This one is made in Japan for Mazda.

The third filter I cut open for comparison was the WIX filter.  Similar in physical size to the Japanese Mazda supplied filter and made in Mexico for WIX.

I must be noted that all three filters are good quality filters and are of above average quality in manufacture and build.






After cutting the filters open, noting construction and measuring the filter media inside, the results were as per the table below;



Oil Filter Filter Media size Filter Media Area Filter Media Volume Contruction Quality  Cost
Mazda Aust Made 1530x40x0.5mm 61,200 mm2 30,600 mm3 Good $19.95
Mazda Japanese 1420x65x0.6mm 92,300 mm2 55,380 mm3 Good $21.42
WIX 1200x54x0.5mm 64,800 mm2 32,400 mm3 Good $15.25


If we were to assume all other oil filter qualities are equal, eg filter media, the Japanese made Mazda Engine Oil Filter is the clear winner here for my money.  It has significantly more filter media, its 20% thicker and 50% larger in area than the Australian made Mazda oil filter.  The WIX filter is a marginally better than the Australian Mazda Filter and better priced.

All filters featured in this article are stocked and sold by
MIldren Rotary Automotive Services

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A few notes on WIX Oil Filters FYI.

Made with a full metal base plate for superior strength at the double seal & also feature a silicone anti-drainback valve. Glass-enhanced media in WIX oil filters offers greater efficiency, capturing more 10 to 12 micron sized particles than other cellulose/synthetic blend medias.

A History of Excellence
WIX is well-known around the world for its innovative filtration products for the automotive and light truck market. Founded in 1939, the Gastonia, N.C., company earned acclaim during World War II when it created an oil filter out of a paper tube, wooden plugs and yarn when steel was in short supply. In 1954 WIX created the revolutionary spin-on oil filter that was eventually adopted as original equipment on most vehicles.

Today WIX manufactures some of the best oil, air, lube, cabin air, hydraulic, fuel, crank case breather and transmission filtration products on the market. The company is also widely known for its support of NASCAR.

Superior Construction
WIX oil filters have a full metal base plate for superior strength at the double seal. They also feature a silicone anti-drainback valve that stays flexible in extreme temperatures. This improves oil flow and keeps oil in the filter to prevent dry starts.

WIX oil filters use an up-front by-pass valve. This design is superior to top-mounted valves because it helps to keep oil from washing past dirty media and entering the engine. The glass-enhanced media in WIX oil filters offers greater efficiency, capturing more 10 to 12 micron sized particles than other cellulose/synthetic blend medias. They also have a coil steel spring to ensure internal filter parts are sealed properly.

Additional Information
WIX filters are supplemental to AMSOIL Ea filters, but now AMSOIL  offers WIX filtration products that cross to an Ea filter. All WIX filters should be changed in accordance with original equipment manufacturer’s (OEM) recommendations. WIX lube filter change intervals are extended OEM recommendations to match the drain intervals of AMSOIL XL Motor oil. To find the correct filter for your application, consult the Online Product Application Guide.

WIX Racing Filters
AMSOIL is carrying WIX racing filters in addition to filters for more common automotive and light truck applications. WIX has been a part of racing and NASCAR for many years, both as a sponsor and in the race cars. The company’s long-standing relationship with NASCAR not only demonstrates that WIX filters are high-quality products, but it also shows WIX’s dedication to racing, making it a perfect match for AMSOIL.

Richard Petty began using WIX filters in 1967, winning six NASCAR championships with the help of WIX filtration technology.  Currently, WIX filters are used on more than 20 Sprint Cup cars, including those of two-time champion Tony Stewart and 2007 Raybestos Rookie of the Year Juan Pablo Montoya.  WIX is also an associate sponsor of Joe Gibbs Racing and maintains a partnership with Toyota Racing Development (TRD).

WIX racing filters are specially designed for racing applications and are not intended for normal driving applications. AMSOIL will carry all WIX racing filters, which includes 10 oil, 14 air and 2 fuel filters.