NTPOG Oil Filter Review

Author: Gerhard Bartsch
Intro by Todd Marcucci

It has been quite a few years since we began this analysis of filters. The original NTPOG article has generated quite a bit of feedback (both good and bad) regarding the content, test methods, and conclusions. We are pleased to present to you a complete overhaul of our testing.

Many, MANY thanks go out to all the people that submitted filters to us and provided us with positive feedback and suggestions for the study. A special thanks from ALL of NTPOG and I know much of the Honda community goes to Gerhard for taking the time to carry on this study which we in the club simply did not have the time/resources to do.

What this review is: The purpose of this review is to examine the different filters available for Hondas today, including Honda filters themselves. Most people probably don't realize it, but there are at least 3 different Honda filters (with different part numbers, made in 3 different countries! All happen to be very different, as well.

What this review is NOT: This review contains no SAE or ASTM test data regarding filtration ability or flow information. This data changes often (as do the filter designs) and in some cases is not even available (publicly) from a manufacturer. If you are interested in actual filtration information, your best option is to review the data yourself (contact the manufacturers) and do your own oil test/analysis (see below). The information presented here is intended solely to help you determine which filter is right for you from the stanpoint of construction. We also hope to have done the "difficult" work for you as you probably don't want to spend the hundreds of dollars and hundreds of hours that we have dissassembling filters.

NTPOG makes no claim as to the reliability or performance of any filter presented here, nor does NTPOG accept any responsibility for any damage caused by any filter.

Other "Suggested" Reading
We would like to thank Russell Knize for his Mini-Mopar site and his Oil Filter Study page for "Mini Mopars." It was the motivation and source of methodology for my own interest in Honda filters. Please visit his site for Chrysler-specific info or on filters you do not see presented here.

If you are interested in seeing the "original" NTPOG filter review (by Todd Marcucci), you may view it here. Please note, though, that the filter information is VERY outdated. Please refer to Gerhard's data presented in the following review for more up-to-date information.

Finally, we would like to encourage our readers to search the internet for other sites and articles on oil filters and oil filtration as you will find a lot of good information. Some other sites to try:

BobIsTheOilGuy.com's Message Board

Well, it's been about a year and a half since Todd Marcucci's original oil filter review was posted on the NTPOG web site. During that time Todd has been collecting various oil filters but didn't have the time to review them. As result of that lack of time he sent them to me!

We're going to go over the same things as in the original reviews, but this time we're going to add some more information about oil types, particle sizes, and lab tests.

The majority of this report is going to go over the physical construction of the filter assemblies. One of the first questions to consider is 'Was the filter physically constructed well?' In order to answer that question we are going to take a look at the basic assemblies found in an oil filter, present a number of measurements, and give you a idea of my opinion of the filter's construction.

The above being stated, it's important for you to understand that I am not a chemical engineer or a expert in the construction of oil filters. I do believe that oil filter construction analysis is not rocket science. There are going to be extremely obvious differences that are going help us determine if a filter is well constructed or something that should never be used in your car.

No claim as to the reliability or performance of any filter reviewed here is made. The information contained in this review is used at your own risk.

What Are the Parts of an Oil Filter?
An oil filter generally consists of 5 discrete sections:

  1. The Base, which contains the engine filter seal, mounting threads (outlet hole), and the interior oil filter one-way (anti-drain back) valve.
  2. The Can, which encloses the rest of the filter assembly and is roll mounted to the base.
  3. The Filter, which contains the medium that removes foreign particles from the oil and is mounted on a sturdy frame.
  4. 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.
  5. The Spring, which generally functions to ensure that the filter assembly fits snugly into the base and gasket .

In order:

The Base


The first picture is the external view of the base. The base is (of course) the point that the filter mounts to your engine. At it's center is a threaded outlet hole. Surrounding the outlet hole on the interior is a flexible gasket (second picture) that overlays a series of holes where the oil enters the filter 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 to the oil pan. The gasket is generally called an anti-drain back valve.

The Filter

The filter assembly 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, it the seam can also be glued together. Lastly, most filter assemblies have a by-pass valve installed in their top, and a large hole at their base that fits into the gasket.

The By-Pass Valve
The by-pass valve functions to prevent a clogged filter from rupturing or, just as importantly, from lower oil pressure. The valve also functions to open during sever oil pressure spikes that happen during periods of very high RPM's. Lastly, the by-pass valve also opens when the oil viscosity is too high (aka the oil has thickened due to cold temperatures, or as a result of to long of an extended drain interval). For this reason 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 a synthetic motor oil then this is not a concern all at 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 Can & The Spring
The can is the piece of metal that incases the entire assembly and is rolled into the base in order to create a liquid tight seal.

The spring is usually either of a leaf or traditional 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. (I suspect this standard design allows manufactures not to keep tight tolerances in manufacturing of the filter assembly. As such, if the filter varies 1mm to 5mm in height then the spring would simply adjust and keep the filter in place.)

How Do You Take Apart an Oil Filter?
Last time Todd used a Dremel Tool to remove the can from the oil filters so that the insides could be inspected. This time I was able find an oil filter inspection tool that is very easy to use and cuts the base off the filter cleanly.

The tool is fairly simple. You simply place the filter on the round stud, finger tighten the knob, and turn the can with your hand until it pops off (while tightening the knob as the can turns easier).


Filter Part Number
AC Delco DuraGuard PF1127
Auto Pride CF402AP
CarQuest 85334
Fram x2 XG3593A
Fram Tough Guard TG3593A
Fram Double Guard DG3593A
Fram Extra Guard PH3593A
Hastings LF402
Hastings LF461
Honda OEM (Canada) S30281
K&N HP-1004
ProLine PPL-14459
ProLine PPL-24458
Purolator Premium Plus (Oversized) L24458
Purolator PureONE (Oversized) PL24458
Purolator PureONE PL24459
STP S2808
Union Sangyo 15400-POH-305
Wal-Mart SuperTech ST2808
Wix 51334

The above list is the list of the filters that were physically inspected for the purposes of this review. Additionally, we also inspected the OEM Acura NSX filter, the WEB W-3429 filter, and the Motorcraft FL-2005. These later filters do not fit on the Honda Prelude, but do give it some insights into some other manufacturer's filters.

Oversized Filters
Many folks have an interest in using an oversized filter. Oversized filters have an advantages over OEM sized filters:

  1. Larger oil capacity
  2. Better oil cooling due to the larger can surface area
  3. More filter medium, resulting in less oil flow restriction and longer serviceable life.
  4. Longer engine oil usage.

What are the considerations when looking for an oversized filter? First, it's got to fit the physical space restrictions on the Prelude. This means that it's got to fit behind the engine, have enough clearance between the firewall and the engine, fit the oil filter mounting base plate, and have the same inlet threading (20mm x 1.5mm). Second, the by-pass valve needs to have the relatively same stiffness as the OEM by-pass specification. The reason for this is fairly simple: Too weak a spring will cause the filter to by-pass all the time, and to strong a spring may cause the filter to restrict oil flow and lower oil pressure. The OEM specification is 9-11PSI.

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).

Engine Oil Change Testing
There is only one way to actually prove how well your oil and oil filter are actually working: Send your oil out to a laboratory and have them tell you what is actually in the oil!

I use Black Stone Labs, many other folks use Oil Analyzers. Both companies will send you reports like this:

Notice on the report that I used 10w40 AMSOIL synthetic oil and that the oil was perfectly fine at 6350 miles. The lab indicated that I could be using the oil for a longer interval. I went on to use the same oil for this report with an AMSOIL SDF-44 oil filter for 13500 miles. It turns out that this oil should be changed every 10000 to 11000 miles. I'm still using it, but just changing the oil every 7500 miles with either a Mobil 1, AMSOIL, or Fram x2 filter. (It's simpler to change the oil and the filter at once.)

In addition to giving you an idea as to how well your oil is being filtered, the lab tests show you just what elements are present in the oil. By carefully looking at the list of elements you can determine problems with your engine. The following picture shows a list of elements and their common meaning when present in motor oil:

The biggest advantage to having your oil tested periodically is that you can determine engine component failure prior to the engine actually breaking down. For example: If anti-freeze is found on your oil then you likely have gasket failure of some sort (head gasket). It's probably cheaper to fix the gasket then drive the car until the anti-freeze starts leaking seriously and causes the bearings to fail, etc.

Oil Filter Inspection Information
Currently, I do not have a web version of the oil inspection information. I need to measure a few filters and write up some more information. Information on oil filters in Excel format can be downloaded here:

Click Here to Download the Oil Comparison Spread Sheet (MS Excel)!

Honda Prelude Oil Filter Recommendations
Currently, it appears that there are four options for a decent oil filter for the Prelude with the OEM spec's:

  1. The Mobil 1 oil filter is well constructed and a decent filter. Unfortunately, I'm not been able to get my hands on a stock spec'ed Mobil 1 filter (but have taken apart a few oversized ones). However, I have been able to discern that it's made on the same line as the K&N filter, but will a media that is slightly better at filtration. Based on testing by others I still think this is a really good filter.
  2. The AMSOIL SDF-20 filter is well constructed and lab tests show that it's an excellent filter. At 6350 miles this filter was able to generate the above lab test report and show that 10w40 oil in an H22A4 causes no problems. On the other hand, it's big brother the SDF-44 did not filter oil well at 13,000 miles. Proving that an oversized filter is not always a good thing when it comes to filtration.
  3. The K&N HP-1004 is a great filter. The internal construction is the same as the Mobil 1 filter, but it does not filter the down to as small a particle size. This filter is meant to maintain higher flow while still actively filtering, as opposed to by-passing. Lab tests using Mobil 1 at 7500 miles indicates that this filter works as well as the AMSOIL SDF-20.
  4. The FRAM x2 (and only the FRAM x2 Series) is probably the most heavily constructed filter I've seen so far. Though all of the Japanese made filters were of exceptional quality, the Fram x2 was as good in every way. Of note with the construction were the following features: metal screen backing the media, heavy metal end caps (all other Fram filters have cardboard), and 2 layer filter medium. Lab testing indicates this filter is fine at 5000 miles use with Mobil 1. As with all of the Fram filters and OEM Honda oil filters the x2 uses the standard spring loaded plastic by-pass valve that many people do not like. However, lab tests do not indicate that the valve jams or fails to work. It's possible that a hard enough impact at a sharp angle while the filter was by-passing might cause it to jam open, but I suspect the fluid within the filter would prevent this.

What Not To Use: Bosch, STP, and Wal-Mart Supertech
While both the STP and the Bosch filters were at one point good filters, they are now manufactured off shore of sub-standard parts. The filter assemblies tended not to have even pleats and generally less media than other comparable filters. There was also a complete lack of a well functioning by-pass valve. With most filters there is an obvious and discrete by-pass valve, but with these filters the can spring and the by-pass valve are the same. The real issue is that in order for the filter to properly by-pass the entire filter assembly would have to move down during use. That is actually not possible with filter assembly properly seating into the anti-drain back valve. This means that the by-pass will effectively never work. In the center of the of picture below you see the filter assembly (top) and the can spring/by-pass valve (bottom). (The can spring / by-pass valve would flip over and into the filter assembly.)

Final Notes
A serious word of caution to experimenters: if you are thinking of trying out different/oversized filters, or ones we haven't listed here, be careful! In the course of testing, we tried a Purolator PureOne oversized filter (PL10193); it leaked pretty bad. Upon inspection, the gasket was found to be MUCH too large, large enough that the oversized M1-105 filter (and M1-104, OEM size) gasket actually fit inside it. If you experiment, be very careful, and look over the filter before testing it. Check the filter immediately upon starting the motor and look for leaks. Be sure to keep a watchful eye on it, and monitor oil pressure if possible. Also keep in mind the difference in bypass spring pressures as this may dramatically affect the way your vehicle's oiling system operates. Check with the manufacturer for exact bypass spring specs, most will usually provide this information via simple email contact with you.

Check back, there are more filters on the way. For comments, questions, or to submit a different filter for analysis, please e-mail the author.

This page last updated 9/1/01.