Recently my goto filter has been Purolator PureOne, I had bought them in quantity for my other cars, but since I didn't have any for the OB I had to go to the local auto parts store. The first one I used was a Fram Tough Gard or Ultra Synthetic, can't remember for sure, but the next time and ever since I have used a Wix at the suggestion of the dude at the store who has been there as long as I can remember. He said it had a valve to prevent the reverse flow of oil which would be important for the upside down mount of the filter. OK, as good a reason as any I suppose. So what do the OB Brain Trust say? Which filters are good for the OB and why?
Lord Osis
OE Subaru and WIX are the only oil filters currently on the market that have the Subaru-spec bypass valve rating (OE 23 psi vs. more typical 10-12 psi).
There's a specific forum for oil here if you want to check it out and elsewhere as well.
Stick with OEM which is a strong belief system/bias across many online forums and new car owners. WIX is a great choice.
Practically speaking it doesn't matter. Change it on time and run synthetic.
I don't know who is making the current batch of Subaru filters but I do know that both Purolator and Wix became the same company a year or so ago. They are different product lines though.
If you have the 2.5L engine the 57055 wix seems popular and might be available in their XP line soon to make it even better.
If you have the 2.5L engine the 57055 wix seems popular and might be available in their XP line soon to make it even better.
I'm one of the early members over at BITOG and while I don't post there often, I do keep up with the forum frequently. Take it for what's worth to you, if anything. From what is routinely posted on BITOG from industry people who either make the filters or work for name brand oil companies, there is a general consensus that isn't seriously doubted by other members. They are:
1. Purolator is not a good brand. It used to be but they have QC issues and the pleats in the filters tear letting unfiltered oil into the engine. Much better is out there for only a few dollars more.
2. The M1 or Fram Ultra filters have consistently shown themselves to be the best overall filter in terms of flow rates, filtration percentages, construction, ADBV material, pleat construction and so on. No one else comes close but it comes at a price. Around $10 or so vs. $5-6 for the Subie OEM.
3. Fram makes the blue Subie can. It's made to Subie specs based on very old technology or requirements from them. It meets a price point but is by no means an excellent filter.
4. The high bypass settting is not a necessity and is based on Subie requesting it because their filtering media (that they speced) isn't that good. With a modern filter such as the Ultra or M1 the filter flows extremely well thus rarely putting the filter into bypass mode, if at all. I've spoken with M1 tech support about the bypass setting and they are very aware of it but reply that flow rates with high quality media make the bypass setting a moot point. Fram says the same thing. Also consider the pressure differential which is what causes bypass.
5. The M1 and Ultra are made for long intervals. How is that done when the cans are the same size between lesser capacity filters such as the Subie can? Very easy to answer - It's the filter media and how it's folded in the can aka more pleats. The Subie filter is plain cellulose which is at the bottom end of filtering media. It doesn't hold a lot of crud which is why they want it changed at 6k. M1 uses a combo cellulose and synthetic to get to a 20k guaranteed interval. Ultra uses 100% synthetic which is how they get to their 20k interval but on BITOG Fram openly says they filters are still working as designed and doing their jobs at 30k but it's dialed back on the package since the oil will be long spent by 30k even if the filter isn't.
6. Lastly, no one and I mean no one has ever had a warranty claim denied because they used a non-Subie filter. Subie does not have the cojones to say that M1 and Ultra are inferior products nor the evidence. If the Subie filter was gospel and so superior to anything else on the market, they would require that you use their filter for warranty purposes. They can't and don't do that.
1. Purolator is not a good brand. It used to be but they have QC issues and the pleats in the filters tear letting unfiltered oil into the engine. Much better is out there for only a few dollars more.
2. The M1 or Fram Ultra filters have consistently shown themselves to be the best overall filter in terms of flow rates, filtration percentages, construction, ADBV material, pleat construction and so on. No one else comes close but it comes at a price. Around $10 or so vs. $5-6 for the Subie OEM.
3. Fram makes the blue Subie can. It's made to Subie specs based on very old technology or requirements from them. It meets a price point but is by no means an excellent filter.
4. The high bypass settting is not a necessity and is based on Subie requesting it because their filtering media (that they speced) isn't that good. With a modern filter such as the Ultra or M1 the filter flows extremely well thus rarely putting the filter into bypass mode, if at all. I've spoken with M1 tech support about the bypass setting and they are very aware of it but reply that flow rates with high quality media make the bypass setting a moot point. Fram says the same thing. Also consider the pressure differential which is what causes bypass.
5. The M1 and Ultra are made for long intervals. How is that done when the cans are the same size between lesser capacity filters such as the Subie can? Very easy to answer - It's the filter media and how it's folded in the can aka more pleats. The Subie filter is plain cellulose which is at the bottom end of filtering media. It doesn't hold a lot of crud which is why they want it changed at 6k. M1 uses a combo cellulose and synthetic to get to a 20k guaranteed interval. Ultra uses 100% synthetic which is how they get to their 20k interval but on BITOG Fram openly says they filters are still working as designed and doing their jobs at 30k but it's dialed back on the package since the oil will be long spent by 30k even if the filter isn't.
6. Lastly, no one and I mean no one has ever had a warranty claim denied because they used a non-Subie filter. Subie does not have the cojones to say that M1 and Ultra are inferior products nor the evidence. If the Subie filter was gospel and so superior to anything else on the market, they would require that you use their filter for warranty purposes. They can't and don't do that.
Interesting thread,
I've read a lot about this and FWIW this is what I've come up with: The CarQuest Red filter from Advance Auto Parts (#R84712) does carry a 23 PSI bypass rating. I believe these to be re-boxed Purolator classic units. Now, does Purolator suck, do they tear as emphasized on the internet? I don't know.
What I do know is this: With a 25% off coupon code I can get these filters for $2.84 each in hand. I can get Pennzoil Platinum for $12.47 + tax (after rebate) for 5 qts. I perform my own oil changes for $15.31 + tax with full synthetic oil and a filter which meets the warranty requirements.
My Outback performs very nicely with this combination. I recycle the oil and filter free of charge. I dump it at 6,000 miles and am very prideful about this process. I am as meticulous as the next, and have been relying on Purolator classic oil filters for my entire 16 years of maintaining my vehicles. Never an oil related issue. I did start with the Blue OEM filters, I find these Purolator's to be better constructed.
*This concerns a 2017 2.5 boxer engine.
I've read a lot about this and FWIW this is what I've come up with: The CarQuest Red filter from Advance Auto Parts (#R84712) does carry a 23 PSI bypass rating. I believe these to be re-boxed Purolator classic units. Now, does Purolator suck, do they tear as emphasized on the internet? I don't know.
What I do know is this: With a 25% off coupon code I can get these filters for $2.84 each in hand. I can get Pennzoil Platinum for $12.47 + tax (after rebate) for 5 qts. I perform my own oil changes for $15.31 + tax with full synthetic oil and a filter which meets the warranty requirements.
My Outback performs very nicely with this combination. I recycle the oil and filter free of charge. I dump it at 6,000 miles and am very prideful about this process. I am as meticulous as the next, and have been relying on Purolator classic oil filters for my entire 16 years of maintaining my vehicles. Never an oil related issue. I did start with the Blue OEM filters, I find these Purolator's to be better constructed.
*This concerns a 2017 2.5 boxer engine.
Our '14 came with a black filter but the local dealer stocks only the blue filters. I buy 'em by the case.
At the risk of seeming OCD/anal/pedantic...is there some overarching cosmic prohibition to my learning: 1) Why is Suburu's oil filter bypass spec unusually high at 23.2psi and 2) Is it important?
I have phoned/e-mailed/written to ALL of the aftermarket filter makers. I have phoned/e-mailed/written to Subaru dealer and Subaru corporate. I have spent hours on the internet (including here) poring over information gleaned from countless posts. Basically, Subaru's bypass spec is 23.2 psi and ALL of the aftermarket filters, if they disclose at all, are 8-17psi. NOT ONE of these sources has answered my questions with other than boilerplate/platitudes/pollyanna responses.
My vehicle is 2018 Outback Limited 3.6 R. Planning to keep it indefinitely so would prefer to avoid being stupid. I want to use the best available and it is clear to me that aftermarket designs are superior to Subaru OEM...except for that bypass spec. I don't understand why actual answers to my two simple questions is so elusive.
If you have any wisdom to offer on the topic, I would LUV to learn!
I have phoned/e-mailed/written to ALL of the aftermarket filter makers. I have phoned/e-mailed/written to Subaru dealer and Subaru corporate. I have spent hours on the internet (including here) poring over information gleaned from countless posts. Basically, Subaru's bypass spec is 23.2 psi and ALL of the aftermarket filters, if they disclose at all, are 8-17psi. NOT ONE of these sources has answered my questions with other than boilerplate/platitudes/pollyanna responses.
My vehicle is 2018 Outback Limited 3.6 R. Planning to keep it indefinitely so would prefer to avoid being stupid. I want to use the best available and it is clear to me that aftermarket designs are superior to Subaru OEM...except for that bypass spec. I don't understand why actual answers to my two simple questions is so elusive.
If you have any wisdom to offer on the topic, I would LUV to learn!
Kevin: No Wix, Napa Gold or Platinum filter for the Subaru 3.6 has a bypass spec of 23psi. Except for the 57055 at 27psi (which doesn't fit my car) they are all far less. I have found nothing other than Subaru OEM that matches the 23.2psi spec...which is why I posted...in desparation. I understand and agree with the rest of what you wrote.
Ammcinnis: 57055 Wix is for the four, not for the six. 27psi doesn't match the spec. in any event.
I have no doubt there is a "sound engineering reason" for the spec. What I don't understand is why it's apparently such a damned secret.
Frequently mentioned in the various posts, there is also the Wix 57012 which has 23psi spec but is not for the 3.6 and, even if it was, is physically so much smaller than other filters it really can't be considered.
Interestingly, ALL of the aftermarket filter makers stand behind the filters they recommend for my vehicle even though ALL of them acknowledge their specs are significantly different.
Ammcinnis: 57055 Wix is for the four, not for the six. 27psi doesn't match the spec. in any event.
I have no doubt there is a "sound engineering reason" for the spec. What I don't understand is why it's apparently such a damned secret.
Frequently mentioned in the various posts, there is also the Wix 57012 which has 23psi spec but is not for the 3.6 and, even if it was, is physically so much smaller than other filters it really can't be considered.
Interestingly, ALL of the aftermarket filter makers stand behind the filters they recommend for my vehicle even though ALL of them acknowledge their specs are significantly different.
Pressure differential is the reason for the bypass consternation.
Unless there's a pressure differential triggering event, a modern high flowing filter never enters bypass. It's that uncomplicated. A new filter such as a Fram Ultra, has extremely high flow rates with synthetic media. The filter does not enter bypass because of the pressure differential factor, outside of some rate events.
All of my UOAs on my car have been posted here on the forum and not a bc single one is with the factory blue. All Fram Ultra and wear rates have been very low.
The Subie bypass setting has a function but today the setting is largely outdated. Same with the recommendation to use conventional oil when modern syn is far superior to any conventional.
Unless there's a pressure differential triggering event, a modern high flowing filter never enters bypass. It's that uncomplicated. A new filter such as a Fram Ultra, has extremely high flow rates with synthetic media. The filter does not enter bypass because of the pressure differential factor, outside of some rate events.
All of my UOAs on my car have been posted here on the forum and not a bc single one is with the factory blue. All Fram Ultra and wear rates have been very low.
The Subie bypass setting has a function but today the setting is largely outdated. Same with the recommendation to use conventional oil when modern syn is far superior to any conventional.
I imagine the bypass is there in case the filter gets so plugged up that you wont destroy your engine. This risk can be avoided or significantly reduced with frequent oil changes. Also, how can you possibly go wrong with the OEM filter? I thought all the test have shown the OEM filter is better almost in every case.
Better only in that it costs less than better filters.
Filter construction is somewhat complicated but the Subie blue is made by Fram for them to Subie specs. It is almost the same as the orange Fram except for the bypass setting.
Yes, if the filter is plugged it goes into bypass on the belief that dirty oil is better then no oil or if on a very cold day you get in the car and floor it just as soon as it starts.
Otherwise, flow is what keeps it from going into bypass and that's wonderfully addressed by other filter manufactures by the media type and how much there is. That's why the Fram Ultra and M1 filters work very well out to 20k. The Fram uses syn media and there's a lot in there. It filters better than a pure cellulose filter but does so without being dense. As a result, the pressure differential does not come into play leading to bypass.
Look at the micron ratings from the Ultra or M1. Much better than the blue can. They are simply far superior filters, but they do cost more.
Filter construction is somewhat complicated but the Subie blue is made by Fram for them to Subie specs. It is almost the same as the orange Fram except for the bypass setting.
Yes, if the filter is plugged it goes into bypass on the belief that dirty oil is better then no oil or if on a very cold day you get in the car and floor it just as soon as it starts.
Otherwise, flow is what keeps it from going into bypass and that's wonderfully addressed by other filter manufactures by the media type and how much there is. That's why the Fram Ultra and M1 filters work very well out to 20k. The Fram uses syn media and there's a lot in there. It filters better than a pure cellulose filter but does so without being dense. As a result, the pressure differential does not come into play leading to bypass.
Look at the micron ratings from the Ultra or M1. Much better than the blue can. They are simply far superior filters, but they do cost more.
FWIW...in recent conversations with a number of independent service facilities specializing in Subaru where I live, I learned that ALL of them use and recommend various aftermarket filters in addition to Subaru OEM filters. NONE of them were aware of the bypass spec or had any idea if such a thing was important. ALL of them said they had seem no problem related to any aftermarket filter. My Subaru dealer, of course, uses only the Subaru OEM filter and they, too, said they encountered no filter-related problems.
So...maybe I'll just buy the Subaru OEM filters and forget it. My annoyance will, doubtless, abate in due course. And I do, actually, have a life aside from my temporary filter obsession. Cost isn't a consideration. I just want to do the best thing in terms of making my car last. (I do use synthetic oil...presently dealer-supplied Idemitsu)
So...maybe I'll just buy the Subaru OEM filters and forget it. My annoyance will, doubtless, abate in due course. And I do, actually, have a life aside from my temporary filter obsession. Cost isn't a consideration. I just want to do the best thing in terms of making my car last. (I do use synthetic oil...presently dealer-supplied Idemitsu)
@Kevin,
The 14.5 GPM figure you mention is a bit out of context but that's because the figure itself needs context.
That figure is based on redline operation of the engine at 6k RPMs. At normal use RPMs the flow rate might be 5 or even less but there's additional necessary context.
The pump is positive displacement and it only will flow at a certain psi, regardless of what the filter bypass might be. It had its own relief valve. The pump only puts out what the engine is capable of handling so saying the oil pump puts out 14.5 is not the correct entire picture.
The 14.5 GPM figure you mention is a bit out of context but that's because the figure itself needs context.
That figure is based on redline operation of the engine at 6k RPMs. At normal use RPMs the flow rate might be 5 or even less but there's additional necessary context.
The pump is positive displacement and it only will flow at a certain psi, regardless of what the filter bypass might be. It had its own relief valve. The pump only puts out what the engine is capable of handling so saying the oil pump puts out 14.5 is not the correct entire picture.
Bypass Pressure
I know this is an old thread but for some reason, it popped up on my phone's news feed just yesterday. I'm sure someone will give me crap for reviving a year plus old thread.
After working in an industrial setting for a number of years, some of my experience has dealt with filtration; I'm willing to take a really **** good stab at your question regarding why Subaru chose the 23psi bypass pressure.
I think the short answer is that they didn't, it's just what that filter comes with. In my experience the bypass is there to protect the filter media, that's why it varies by the type of filter, because different materials can withstand different degrees of differential pressure. I agree unfiltered oil flowing through your engine would suck, but how would you like that unfiltered oil carrying hunks of your destroyed oil filter through the engine?
I know this is an old thread but for some reason, it popped up on my phone's news feed just yesterday. I'm sure someone will give me crap for reviving a year plus old thread.
After working in an industrial setting for a number of years, some of my experience has dealt with filtration; I'm willing to take a really **** good stab at your question regarding why Subaru chose the 23psi bypass pressure.
I think the short answer is that they didn't, it's just what that filter comes with. In my experience the bypass is there to protect the filter media, that's why it varies by the type of filter, because different materials can withstand different degrees of differential pressure. I agree unfiltered oil flowing through your engine would suck, but how would you like that unfiltered oil carrying hunks of your destroyed oil filter through the engine?
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I always run factory filters due to cost and peace of mind for a quality filter. Not sure about everyone else but the dealer around me charges $9 with a new crush washer. NAPA sells their filters for $11, K&N for $18, Walmart FRAM/Generic filters are $7. Non of these come with a crush washer so I still need to stop at the dealer and spend an extra $1.
It's a no brainer for a OEM filter.
It's a no brainer for a OEM filter.
where to start....Most oil filters today do amazing job for what they were design--Hold dirt . If you not doing extended oil changes (10-12K km's or more) i don't see the need for expensive filters. 1 micron, 2 microns to me, all BS to sell overpriced filters. Any major brand and OEM filters will be just fine. Extended oil changes it's more about the quality of the filtration media than how small the microns it can hold. The vast majority of oil filter "failures" i have seen, was not filters fault at all. From filters installed with full plastic wrapper still on, to double gasket filters, wrong application, cut gaskets, missing gaskets, crazy over-tight filters.. I can remember very few instances of real failed filter, and those few; almost all was from the .59cent one size fits all bin. At end of the day, any good quality filter will be fine on an Outback. I guess Oil Filters and Oil brands are a sensitive issue for some 
I wanted to follow up, after having done extensive research on what has been discussed, to say that I am giving my personal recommendation to the Fram Ultra Synthetic oil filter. I have used this filter before on my Outback with good results but I too had been hung up on the 23psi bypass spec in the past.
One interesting piece of information I came across stated that the Fram Ultra XG7317 filter (used on Subaru 2.5L) has a max output of 18 gallons per minute, including tested verification. All of this info is easily found on BITOG, that and a discussion from all the way back in 2009 with a technical readout of all of Subaru's dread oil pump specs.
Of note is the specific reference to the specific oil filter utilized by Subaru to accomodate this oil pump. It very clearly states that the filter media is paper (cellulose) and it is well know that this type of filter media is flow restrictive as compared to the newer, more advanced synthetic filter media like say in a Fram Ultra Synthetic oil filter. So I deduce that the Subaru OEM oil filter has a 23psi bypass due to the filter media that allows for a max flow rate of 14.5 gallons per minute. WIX/NAPA uses a 27psi bypass and I deduce that it is because their filters are limited to a 10 gallon per minute flow rate perhaps due to the size specs of their filters, media, etc.
My conclusion is that the bypass spec is determined by the variables of a SPECIFIC FILTER which means not all are required to have the same bypass spec to function as intended. Lower flow rate = higher bypass (ie WIX/NAPA), higher flow rate = lower bypass (ie Fram Ultra). Based on the test information I have seen on the Fram Ultra its flow rate is so high that it effectively cuts the PSID in half when used with an appropriate oil, that means that the Ultra's 13 psi bypass is equivalent to or even exceeds the WIX/NAPA 27psi bypass.
One interesting piece of information I came across stated that the Fram Ultra XG7317 filter (used on Subaru 2.5L) has a max output of 18 gallons per minute, including tested verification. All of this info is easily found on BITOG, that and a discussion from all the way back in 2009 with a technical readout of all of Subaru's dread oil pump specs.
Of note is the specific reference to the specific oil filter utilized by Subaru to accomodate this oil pump. It very clearly states that the filter media is paper (cellulose) and it is well know that this type of filter media is flow restrictive as compared to the newer, more advanced synthetic filter media like say in a Fram Ultra Synthetic oil filter. So I deduce that the Subaru OEM oil filter has a 23psi bypass due to the filter media that allows for a max flow rate of 14.5 gallons per minute. WIX/NAPA uses a 27psi bypass and I deduce that it is because their filters are limited to a 10 gallon per minute flow rate perhaps due to the size specs of their filters, media, etc.
My conclusion is that the bypass spec is determined by the variables of a SPECIFIC FILTER which means not all are required to have the same bypass spec to function as intended. Lower flow rate = higher bypass (ie WIX/NAPA), higher flow rate = lower bypass (ie Fram Ultra). Based on the test information I have seen on the Fram Ultra its flow rate is so high that it effectively cuts the PSID in half when used with an appropriate oil, that means that the Ultra's 13 psi bypass is equivalent to or even exceeds the WIX/NAPA 27psi bypass.
Just to add something to a bypass pressure specific oil filter thread - Subaru is not unique in that regard, and it's not just for some spurious reason. Also consider that "flow rate" depends on viscosity and viscosity changes with temperature and different oil grades have different viscosity, so any given X gallons per minute spec for filtering media is for a given viscosity oil at a given temperature (and pressure). Using a low bypass pressure filter at low temperatures with high viscosity oil is a worst case scenario for cold start filter bypass.
GM switched to 22 psi bypass pressure spec and the linked TSB explains why.
BITOG thread about it: Wix updates Gen V oil filter specs - 22 PSI bypass
In 2009 with the Series 2 RX-8, Mazda changed from a low bypass pressure to high (20+ psi) bypass pressure filter, at the same time that they changed their oil pump to a higher flow one. (Subarus also have high flow oil pumps)
Isuzu also switched to a higher (unspecified) bypass pressure oil filter but cautions not to use it on vehicles that were specified for a low bypass pressure because of potential oil starvation.
All I'm saying is that bypass pressure isn't something that only Subaru is some quirky unicorn manufacturer that out of pure randomness ended up with this 20+ psi bypass spec and has just stuck with it out of inertia.
Other manufacturers have followed Subaru in going to higher bypass pressure filters, and for cold-start reasons - but this does not mean that a higher bypass pressure is always better.
GM switched to 22 psi bypass pressure spec and the linked TSB explains why.
BITOG thread about it: Wix updates Gen V oil filter specs - 22 PSI bypass
In 2009 with the Series 2 RX-8, Mazda changed from a low bypass pressure to high (20+ psi) bypass pressure filter, at the same time that they changed their oil pump to a higher flow one. (Subarus also have high flow oil pumps)
ONLY USE GENUINE Mazda OIL FILTERS in Series II (R3) - RX8Club.com
Series II Technical and Trouble shooting - ONLY USE GENUINE Mazda OIL FILTERS in Series II (R3) - Series II RX-8 owners... I have noticed many aftermarket brands of Oil Filters are still recommending the same OIL Filter that is used on the Series 1 RX-8's...TOTALLY INCORRECT. You may not be...
www.rx8club.com
Isuzu also switched to a higher (unspecified) bypass pressure oil filter but cautions not to use it on vehicles that were specified for a low bypass pressure because of potential oil starvation.
All I'm saying is that bypass pressure isn't something that only Subaru is some quirky unicorn manufacturer that out of pure randomness ended up with this 20+ psi bypass spec and has just stuck with it out of inertia.
Other manufacturers have followed Subaru in going to higher bypass pressure filters, and for cold-start reasons - but this does not mean that a higher bypass pressure is always better.
Our member @Mott Power posted a most excellent explanation in a thread I came across recently:
"The bypass setting is based on PSID; the difference between the inlet and outlet pressure of the filter, not in relation to absolute pressure from the oil pump (which is variable to rpm). Meaning the bypass opens if the difference in pressure prior to the filter is greater than 23 psi compared to the pressure after the oil filter, no matter if you're measuring 25 psi or 60 psi to the filter.
If you're running 40 psi from the pump, that doesn't mean the oil filter is bypassing all oil after 23 psi. Rather, if the inlet pressure to the filter is 40 psi and the outlet pressure is 17 psi, then it will open (similar in some regards to how intake bypass valves operate on turbocharged vehicles). N4HHE & idosubaru were right on the money in regards to their posted explanations.
Oil filter bypass numbers are a factor of the flow rate of the filter element (surface area and density) vs the viscosity of the oil. Oil viscosity is a constant at 0w-20 for our vehicles. If you change the filter element's flow rate, then you can variably adjust the bypass setting. Hence why some manufacturers have lower ratings but still call for it be used on our Outbacks. This doesn't mean they will operate in bypass "99% of the time"... It will function virtually the same way, but the argument you run into is how much of the particulates are being filtered if it has a higher or lower flow rate through the element (whole other discussion...).
Subaru's oil pressures are not much different than other systems; I have measured flow rates on various other cars and it's not much different from what the service manual states."
www.subaruoutback.org
"The bypass setting is based on PSID; the difference between the inlet and outlet pressure of the filter, not in relation to absolute pressure from the oil pump (which is variable to rpm). Meaning the bypass opens if the difference in pressure prior to the filter is greater than 23 psi compared to the pressure after the oil filter, no matter if you're measuring 25 psi or 60 psi to the filter.
If you're running 40 psi from the pump, that doesn't mean the oil filter is bypassing all oil after 23 psi. Rather, if the inlet pressure to the filter is 40 psi and the outlet pressure is 17 psi, then it will open (similar in some regards to how intake bypass valves operate on turbocharged vehicles). N4HHE & idosubaru were right on the money in regards to their posted explanations.
Oil filter bypass numbers are a factor of the flow rate of the filter element (surface area and density) vs the viscosity of the oil. Oil viscosity is a constant at 0w-20 for our vehicles. If you change the filter element's flow rate, then you can variably adjust the bypass setting. Hence why some manufacturers have lower ratings but still call for it be used on our Outbacks. This doesn't mean they will operate in bypass "99% of the time"... It will function virtually the same way, but the argument you run into is how much of the particulates are being filtered if it has a higher or lower flow rate through the element (whole other discussion...).
Subaru's oil pressures are not much different than other systems; I have measured flow rates on various other cars and it's not much different from what the service manual states."
Oil filter other than SUBARU brand?
Nope. The "rule of thumb" benchmark for many years was 10 psi per 1,000 rpm. From the 2015 Legacy/Outback Factory Service Manual, FB25 engine: 2-stage pressure control valve 1st stage opening pressure = 21.7 psi Main opening pressure = 82.6 psi Pressure at 600 rpm: >5.8 psi Pressure at 6,000...
www.subaruoutback.org
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