Grease is the Word

Oil Filter Study

Concentrating on the AC PF1218 and its equivalents

Including some Mercruiser, FL400s, and FL820s applications

With Pore and Flow Measurements

Version 3.0

May 25, 2004


This oil filter study was originally started to determine if there was a better oil filter for the Mercruiser oil filter found on Chevrolet / Mercruiser inboard and I/O applications.  It then grew to compare many manufacturers' equivalents to the AC PF1218.  The AC PF1218 (and the Fram PH5) are used on a wide variety of vehicles particularly the GM V8.

The study was motivated and inspired by the discussions on the forums at Bob is the Oil Guy (BITOG).  There you will find several forums discussing every aspect of lubrication and one dedicated to oil filters.  The phrase above "Grease is the Word" is the author's screen name on the forums at BITOG.  You can communicate with the author on BITOG via personal messaging or email.


This study could not have been completed without the help from many individuals, but mostly one BITOG member (who chooses to remain anonymous) that completed the bubble point and flow tests.  He spent hours testing and retesting oil filter media.  In fact, for this version (3) which added eight more media, he retested the original 12 filters to ensure that the testing was accurate.

Additional BITOG members provided financial support by donating money or filters:

Approximately 200 hours and about $150 have been spent on this project and has been about 6 months in the making to get to this point.  This site requires $35 a year to remain on-line.  If you have benefited from the material, please consider making a $1 Paypal donation to defer the cost of domain and web site costs.  This will allow this site to remain on-line for longer than the first year.


Here are some definitions used throughout this study.

Testing Scope

In addition, the following measurements are made on the filter media:

Testing Background

The bubble point testing was performed using a similar bubble point tester to this unit.


Study Scope

This study concentrates on 18 AC PF1218 equivalents.  These include the following filter models (in alphabetical order).  The reader can click on a filter to show details, photos, and descriptions.  Each link will open a new browser window.  Within each filter page there are thumbnail pictures.  To enlarge a picture, click on the thumbnail.  To return to the specific filter page, click the back button on your browser.

* The AC UPF1218 is no longer manufactured.  It was included in this test to evaluate the media and provide a reference for the remainder of the UPF line still available.

** The AC PF35L is not a "true" equivalent since it does not have an ADBV.  Otherwise it has the same dimensions as a PF1218.  It was included in this test because of its synthetic media.

Two Mercruiser application filters are compared:

The media from three other filters are also tested and shown in the testing data spreadsheet.

  • Donaldson Synteq media
  • WIX Racing media (from S1515R)
  • Parker Hydraulic filter #921999 a 20gpm filter with β10=2 efficiency (captures 50% of 10µm particles)

The Parker hydraulic filter can be used as a filtration benchmark because of its rated efficiency. Any of the filters above the Parker filter in the spreadsheet will provide better than 50% reduction in 10µm particles and any below it will provide less than 50% reduction in 10µm particles in a multi-pass test.

In addition, five filters representing the Motorcraft FL400s and FL820s are and shown in the testing data spreadsheet.  While there are not pictures included of these filters, they do have their EFA, flow, and pore size calculated.

In the filters above, the media was the same as their PF1218 counterparts.  For example, the Fram TG2 media tested the same as the Fram TG5.  The Fram TG2 EFA is then measured and compared to other FL820s filters. 

Filter Testing Data

The tabulated data for this study can be found in MS Excel spreadsheet below (note:  if you do not have MS Excel on your computer, you can download a free viewer from Microsoft using this link).

Grease Oil Filter Study Spreadsheet

The intent of this study is to be as objective and non-biased as possible and just present observations.  This data is collected in the above spreadsheet on two different tabs or worksheets.  The first one is called Filter Data and contains physical measurements and observations.  The second tab is called Bubble Point Testing and contains the results of the media pore size and flow tests.

Within the Bubble Point Testing tab filter names are either regular font, bold, or italics.  The bold filters indicate an AC 1218 equivalent, and italics indicate a Mercruiser application (shorter canister to the 1218 filters).

Viscosity vs. Temperature

The tests in this study were done using 70F 30 grade oil.  To give the reader a sense for how oil changes viscosity with temperature change, click here to view this chart that compares different oils at different temperatures.

Filter Media

Click here for a page that has charts that describe more about filter media, industry testing, and the manufacturing process of media.


Good construction, good flow, good filtering

In the low-priced group, the AC PF, Purolator PremiumPlus, STP, and SuperTech appear to be good choices.  These four filters are "best buys" because they doing most things well and are in the low-priced group.

In the mid-priced group, the Baldwin and WIX appear to be good choices.  Both have construction that is excellent.

In the high-priced group, the Amsoil, Mobil 1, Fram XG, and K&N appear to be good choices.

Excellent filtering

The Fram TG and Purolator PureOne have excellent filtering.  They do flow less than filters with less filtering.  Both are in the mid-priced group.  The AC UPF also has excellent filtering, however, the UPF1218 is no longer manufactured.  The UPF series does include other filter applications that are still available.

Excellent flow

The Hastings, Donaldson, and Fleetgard all have excellent flow.  Not surprisingly, they are also have larger pore sized media.  The Purolator PremiumPlus and Amsoil flow less than these filters, but still better than average and have good or very good filtration.

The reader should also consider using an excellent flowing filter and add a by-pass filter such as an Oilguard, Amsoil, or Motor Guard.

Mercruiser Conclusions

The Mercruiser filter is a high-flowing filter with larger pore size.  The WIX 51086 does not appear to be a good substitute in this application because it flows less than half as well as the Mercruiser.  If one did not mind going to a longer format (the PF1218 style), other excellent candidates would be Hastings, K&N, and Purolator PremiumPlus.  All three of these filters flow just as well or better than the Mercruiser, have better filtration, and give the added benefit of more media / increased sump capacity.  The Amsoil would have to be another viable candidate since it filters much better than the Mercruiser and it flows almost as well.

Click here for more information regarding Mercruiser applications including additional filters and applications.

Disclaimer and cautions

Since many filter manufacturers contract out their filters, one must be careful that future filters from these vendors are the same as what is presented here.  One way to do this is to compare the outside markings of new filters to these pictures.

Just because one filter appears to be a good choice for this application, does not mean that it will be the best for other automotive applications. Other applications involve by-pass valves and other features that may or may not make that same filter the best choice.

Be sure to check your application. There is no guarantee, express or implied, that these filters will work in your application