Reprinted from i Saluti, April 1999, originally from the Mini-Mopar Resource Site

Engine Oil Filter Study

by Russell W. Knize

[This is an edited version of Russell Knize's investigation -- for the complete study click here. Since the Fram PH8A filter fits the Alfa Spider and Milano, it's reasonable to assume that the other filters discussed here will also fit the 4- and 6-cylinder Alfas. It's probably better, however, to check each manufacturer's application book -- RHH]

When it comes down to it, all of the lower-priced filters ($5 or below) have their ups and downs. In reality, there are only four different manufacturers available. Here are the low-cost filters that I feel safe using, based on all this information (in alphabetical order): AC Delco, Purolator, and Wix. Here are my reasons for each:
Recommended Filters Price
AC Delco Duraguard PF2 $3
Purolator Prem. Plus L30001 $3
Purolator Pure One PL30001 $5
Wix 51515 $5
Mobil 1 M1-301 $10
Not recommended Price
Fram Extra Guard PH8A $3
Fram Tough Guard TG8A $5
Fram Double Guard DG8A $10

I like the deep pleats of the AC Delco’s filter element and the fact that it is not weak like the low-end Wix. I also like the way that the anti-drainback valve diaphram makes a positive seal to the filter cartridge and to the bypass valve, which sort of “snaps” into the diaphram. The fact that the bypass valve seats against the backplate metal-to-metal is not a big deal. It probably doesn’t leak anyway, but if it does, only clean oil can get back into the pan. In case you haven’t noticed, I really like this filter.

The Purolator is a very solid design. It seems to have the toughest paper filter element of them all and the bypass valve is built right into the cartridge. There are no internal sealing problems with this filter at all. I wish the inner diameter of the cartridge was smaller so that the pleats could be fewer and deeper. The Premium Plus looks like it flows fine, but the Pure One or Motorcraft versions seem to be packed a bit too tightly. That assembly string still bothers me somewhat, but not enough to avoid these well-made filters completely. My ’88 Shadow ES has a Purolator Premium Plus in it right now. I plan to cut it open and see how it holds up at the next oil change.

I don’t care for the low-end Wix filters. The filter elements are way too fragile to give me much confidense in them. That, along with the rusty backplates, makes me shy away from them. Some decent filter material and a little oil used during assembly would make this into a fine filter. Like the Purolator, I like how the bypass valve is built right into the filter cartridge. This filter has no internal sealing problems, either. Even so, I won’t be using them.

The high-end Wix filter is a very well made filter. Aside from being a stronger case, it also uses a much better filter element (about the same as the AC Delco). Like the AC Delco, it also has a minor internal sealing problem. In this case, the bypass valve has a metal-to-metal seal to the filter cartridge. It probably doesn’t really leak etiher, but if it did, dirty oil could get to the clean side of the filter. Otherwise it is a good filter. Given the choice between the Wix and the AC Delco, I’d take the AC Delco. The Wix is also about twice the price.

If money is no object, I would go with the Mobil 1. Although it has low-end Wix internals, it has a really tough synthetic fiber filter element. The element is stronger and thicker than the Purolator, but they claim that it flows just as good as paper. As with the other low-end Wix filters, it has no internal sealing problems. Mobil 1 got the best of the Wix world. The $10 price tag is a bit steep, but it is the best filter you can buy retail. Watch for “Mobil 1 Oil Change” sales, which includes 5 quarts of Mobil 1 synthetic oil and a Mobil 1 filter. There are probably better filters available through mail order, but I haven’t tested those yet...

I reserve the right to change my opinion at any time. It could esily change if another filter (or one of the filters I am waiting on) comes around and is better.

See the AC Delco, Fram, Purolator, and Wix sections for information on how to identify these manufacturers by looking at the backplate. The tell-tale signs are always there.

Details

AC Delco Duraguard PF2

Some years ago, a study was done on oil filters that uncovered the Fram filter farce. They named AC Delco’s filter to be one of the better models. Later, AC Delco changed their design and went to a cheaper setup made by an offshore manufacturer. Even so, I definately recommend this filter over the design of any Fram filter. In fact, I even recommend it over the low-end Wix and I (personally) prefer it over the Purolators.

The filter cartridge has a large outside diameter with deep pleats, which gives the filter element the maximum flow possible. At first glance, it appears to have little filter element media, but the surface area measure was suprising: 315 sq in. The unit had a solid top end cap because the bypass valve is at the bottom, which is a well-constructed spring-loaded steel with a nitrile seal design. The nitrile rubber diaphram-type anti-drainback valve doubles as the seal between the bypass valve and the cartridge. The only drawback to this design is that the bypass valve seats metal-to-metal against the backplate. This could allow oil from the clean side of the filter to seep back into the oil pan, but it won’t allow the dirty oil in the filter to seep back. Oil that is in the main gallery usually leaks out through the main bearings anyway while the engine sits. This is a better alternative to the high-end Wix, which can allow oil to seep from the dirty side of the filter to the clean side.

The telltale signs for an AC Delco filter are: Five large holes for the oil inlet and 6 spot welds on the rim surrounding them. There are no crimps holding the gasket in place. When you look through the inlet holes, you can see the metal bypass valve with its 12 small holes and the black anti-drainback valve diaphram around it. Through the center outlet hole, you can see the spring for the bypass valve.

Average Retail Price         $3 
Cartridge Length             4.625 inches 
Cartridge OD  3.375 inches, ID  1.375 inches 
Cartridge Pleats             36 
Cartridge End Cap Type       Stamped steel 
Anti-Drainback Valve Type    Nitrile rubber diaphram 
Bypass Valve Type            Spring-loaded steel 
Element Type                 Paper media, glued seam 
Element Length  70.0 inches, Width  4.500 inches 
Element Surface Area         315 square inches 
Shell Thickness              0.015 inches 
Backplate Thickness          0.100 inches 
Gasket Type                  Nitrile rubber 

Fram Extra Guard PH8A

Years ago Fram was a quality filter manufacturer. Now their standard filter (the radioactive-orange cans) is one of the worst out there. These filters are manufactured by Allied Signal, Inc. Please do not buy this filter. By boycotting it, we may be able to cause some change. I have personally had one if these filters fail and actually cause engine damage due to bits of paper and glue floating around in the engine.

This filter cartridge has a small outside diameter with a rather low filter element surface area (193 sq in), and features cardboard end caps that are glued in place. The rubber anti-drainback valve seals against the cardboard and easily leaks, causing dirty oil to drain back into the pan. If you have a noisy valve train at startup, this filter is likely the cause. The bypass valves are plastic and are sometimes not molded correctly, which allows them to leak all the time, but they often leak anyway. The backplate has smaller and fewer oil inlet holes, which may restrict flow, and is made of thin material.

The telltale signs for a Fram Extra Guard are: It has 8 small holes for the oil inlet and a thin, cheap-looking backplate, and is currently stamped with a “2Y”. There are 5 very small crimps holding the gasket in place. If you look into the center hole all the way to the top of the filter, you will see a kind of “button” in the end cap of the cartrige (which looks like it’s made of metal from there). This is the plastic bypass valve.

Average Retail Price         $3 
Cartridge Length             4.125 inches 
Cartridge OD  3.000 inches, ID  1.375 inches 
Cartridge Pleats             34 
Cartridge End Cap Type       Cardboard 
Anti-Drainback Valve Type    Nitrile rubber diaphram 
Bypass Valve Type            Spring-loaded plastic 
Element Type                 Paper media, stamped metal seam
Element Length  47.5 inches, Width  4.063 inches 
Element Surface Area         193 square inches 
Shell Thickness              0.015 inches 
Backplate Thickness          0.089 inches 
Gasket Type                  Nitrile rubber 

Fram Tough Guard TG8A

Even with all the problems of the other Fram filters, this one is not too bad. Aside from the filter cartridge, it is a very good design. Too bad Fram can’t get passed the cardboard end caps.

It has an improved filter element with more surface area (248 sq in), a heavy silicone anti-drainback valve with a good sealing surface, the same plastic pressure relief valve but with an integral screen to keep out large particles, and enough inlet holes for good flow. The only real drawback to this filter is that it is capped on each end with cardboard instead of metal.

The telltale signs for a Fram Tough Gaurd filter are: It has a better backplate that is usually shiny, with six larger holes for the inlet and 6 spot welds around the them. There are 6 large crimps holding the gasket in place. When you look through the inlet holes, you can see the orange anti-drainback valve. If you look into the center hole all the way to the top of the filter, you will see a kind of “button” in the end cap of the cartrige (which looks like it’s made of metal from there). This is the plastic bypass valve.

Average Retail Price         $5 
Cartridge Length             4.125 inches 
Cartridge OD  3.000 inches, ID  1.625 inches 
Cartridge Pleats             50 
Cartridge End Cap Type       Cardboard 
Anti-Drainback Valve Type    Silicone rubber diaphram 
Bypass Valve Type            Spring-loaded plastic with integral screen 
Element Type                 Paper media, stamped metal seam 
Element Length  61.0 inches, Width  4.063 inches 
Element Surface Area         248 square inches 
Shell Thickness              0.015 inches 
Backplate Thickness          0.187 inches 
Gasket Type                  Nitrile rubber, PTFE-treated 

Fram Double Guard DG8A

This is a frustrating filter. Please do not buy it. At $10 it is one of the most expensive filters you can buy and it is junk. Inside is a basic Fram Extra Guard (PH8A) filter element that has larger diameter holes at the end and has been pre-oiled. I assume this is to hold the Teflon particles in the filter element before the unit is installed. Don’t put Teflon in your engine. It does not belong there! DuPont does not recommend using their Teflon product in internal combustion engines.

Although it has the worst filter element possible (193 sq in), it does have a clever spring-loaded nitrile rubber anti-drainback valve and bypass valve combination. Too bad the rest of the filter is worthless. Please don’t buy this filter!

The telltale signs for a Fram Tough Gaurd filter are: It has a better backplate that is usually shiny, with six larger holes for the inlet and 6 spot welds around the them. The backplate should be stamped with a “1K”. There are 6 large crimps holding the gasket in place. The anti-drainback valve diaphram behind the inlet holes is black. If you look into the center hole all the way to the top of the filter, you will not see the “button” in the end cap of the cartrige (which looks like it’s made of metal from there).

Mobil 1 M1-301

Like the Wix, this filter is made by Dana. However, it is a strange hybrid-type design. The cartridge is the better one-piece found in the low-end Dana filters, but it uses the different end plate and a thicker can than any other Dana filter. It also does not use the fragile paper media of the low-end Dana. I’m happy to say that this filter is NOT a fake. It is definately a unique design.

It uses a synthetic fiber element that can filter out very small particles and is much stronger than the fragile, low-end Dana paper media. It is rated 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 and that pesky assembly string. However, as with all Mobil 1 products, expect to pay 2 - 3 times as much for this filter.

Average Retail Price         $10 
Cartridge Length             4.250 inches 
Cartridge OD  3.250 inches, ID  1.625 inches 
Cartridge Pleats             52 
Cartridge End Cap Type       Stamped-steel, with bypass valve 
Anti-Drainback Valve Type    Nitrile rubber diaphram 
Bypass Valve Type            Spring-loaded steel, nitrile seal 
Element Type                 Synthetic media, glued seam 
Element Length  85 inches, Width  4.125 inches 
Element Surface Area         351 square inches 
Shell Thickness              
Backplate Thickness          0.138 inches 
Gasket Type                  Nitrile rubber 
Hydrostatic Burst Pressure   600 psi 
SAE J806 Filter Efficiency    Single pass: 98%, Multiple pass: 95% 

Purolator Premium Plus L30001

Here is a fairly well designed filter, especially for the price. One odd thing about Purolator’s filters is a string that is always wrapped around the filter element. I assume that this is there to hold the element in place while the glue in the end caps cures. Of all the Purolator-based filters I tested, there was one (the ProLine) that had filter element damage from this string. Although it was one of five tested, I am wary of this design. Even though the element was crushed a bit, it was not ripped. I will take apart a used one at my next oil change.

The filter cartridge has an impressive surface area of 316 sq in, which is very close to the AC Delco Duraguard. The difference is that Purolator’s filter element is compressed into more pleats (51) than the AC Delco. This may restrict flow somewhat, but not as much in this model than the Pure One. It features a spring-loaded metal bypass valve and a nitrile rubber diaphram-type anti-drainback valve, which doubles as the seal between the backplate and the cartridge. Like the low-end Wix, this bypass valve is stamped right into the bottom end cap of the cartridge, so it is all one piece.

The telltale sign for a Purolator filter are: 8 medium-sized holes for the oil inlet and nothing but a black (or orange for the Pure One) diaphram to be seen through them. There are 6 large crimps holding the gasket in place. Through the center outlet hole, you can see the spring for the bypass valve.

Average Retail Price         $3 
Cartridge Length             4.125 inches 
Cartridge OD  3.250 inches, ID  1.625 inches 
Cartridge Pleats             51 
Cartridge End Cap Type       Stamped-steel 
Anti-Drainback Valve Type    Nitrile rubber diaphram 
Bypass Valve Type            Spring-loaded steel 
Element Type                 Paper media, stamped metal seam
Element Length  79.0 inches, Width  4.000 inches 
Element Surface Area         316 square inches 
Shell Thickness              0.011 inches 
Backplate Thickness          0.115 inches 
Gasket Type                  Nitrile rubber 

Purolator Pure One PL30001

This filter has a few improvements over the Premium Plus. It has a denser filter media to filter out smaller particles and more surface area to make up for the flow restriction. Aside from those the cartridge is the same construction as the Premium Plus.

The filter cartridge has an even more impressive surface area of 400 sq in. The potential issue is that this filter element is compressed into even more pleats (64) than the Premium Plus. This may restrict flow more than it helps relieve it. It also features a spring-loaded metal bypass valve and a silicone rubber diaphram-type anti-drainback valve, which doubles as the seal between the backplate and the cartridge. The bypass valve is located at the base of the cartridge, not at the top.

Average Retail Price         $5 
Cartridge Length		4.250 inches
Cartridge OD  3.250 inches, ID  1.625 inches 
Cartridge Pleats             64 
Cartridge End Cap Type       Stamped-steel 
Anti-Drainback Valve Type    Silicone rubber diaphram 
Bypass Valve Type            Spring-loaded steel 
Element Type                 Paper media, stamped metal seam 
Element Length  100.0 inches, Width  4.000 inches 
Element Surface Area         400 square inches 
Shell Thickness              0.011 inches 
Backplate Thickness          0.115 inches 
Gasket Type                  Nitrile rubber, PTFE-treated 
SAE J806 Filter Efficiency    Single pass: 99.7%, Multiple pass: 96% 

Wix Low-end Filter

These filters are manufactured by the Dana corperation, who also manufactures all of the Wix clones. These include the Car And Driver, Deutsch, Mobil 1, NAPA, STP and others. There seems to be two filter designs that Dana uses.

The first design I will refer to as the low-end Wix filter. It has metal end caps on the filter cartridge, with the bypass valve stamped right into the bottom end cap like the Purolator. I refer to this as the one-piece filter cartridge. Though definately not the same design as the Purolator, it does use the same type of leaf-spring-type spacer at the top of the cartridge and the nitrile anti-drainback valve, which doubles as the cartridge-to-backplate seal, at the bottom. The drawback to this one-piece cartridge is the rather fragile filter element paper media. It is a thin, brittle paper that rips fairly easily. It was difficult to disassemble these cartiridges without destroying the filter element. One other issure is that I sometimes noticed some rust on the backplate of these filters. Since the rust is usually around by the inlet holes, any loose rust would be caught by the filter.

The second design I will refer to as the high-end Wix filter. It also has metal cartridge end caps, but has a seperate bypass valve that rests against the bottom end cap, like the AC Delco. I refer to this as the two-piece filter cartridge. Like the other Wix design, it uses a similar anti-drainback valve that doubles as the bypass valve-to-backplate seal. Instead of the leaf-spring-type spacer that most filters use, these use a coil spring at the top of the cartridge. Like the Purolator, the filter element paper media is stronger than the low-end Wix media. This, and because it is more expensive, is why I call this filter the high-end design. The only drawback to this design is that the bypass valve seats metal-to-metal against the bottom cartridge end plate. This could allow dirty oil to seep from the dirty side to the clean side of the filter, bypassing the element. The design will not allow oil to seep back into the pan, though.

The telltale signs for a low-end Wix are: 6 large holes for the oil inlet, one of which is larger than the others. Only the black anti-drainback valve can be seen through the inlet holes. There are 6 large crimps holding the gasket in place. Through the center outlet hole, you can see the bypass valve spring. Usually, the backplate metal is dull, or even rusty.

The telltale signs for a high-end Wix are: 6 large holes for the oil inlet with only the black anti-drainback valve to be seen through them. There are 6 “notches” that hold the gasket in place. Through the center outlet hole, you can see the bypass valve spring. Usually the backplate metal is shiny.

Wix 51515

This filter is the high-end Wix filter, as described above. It features a good surface area, but a lot of shallower pleats. This makes it similar to the Purolator’s pleats.

Average Retail Price         $5 
Cartridge Length             4.000 inches 
Cartridge OD  3.250 inches, ID  1.625 inches 
Cartridge Pleats             61 
Cartridge End Cap Type       Stamped-steel 
Anti-Drainback Valve Type    Nitrile rubber diaphram 
Bypass Valve Type            Spring-loaded steel, nitrile seal 
Element Type                 Paper media, glued seam 
Element Length  90 inches, Width  3.875 inches 
Element Surface Area         349 square inches 
Shell Thickness              0.014 inches 
Backplate Thickness          0.104 inches 
Gasket Type                  Nitrile rubber