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?
The magical/mystical 23.2psi oil filter bypass spec.
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Lord Osis
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Some more to chew on from yours truly:
"The reality is, and I have daisy chained several threads together on BITOG in the past to substantiate this conclusion, that the bypass spec of Subaru's OEM oil filter what established due to a few factors:
1. In model year 2009 Subaru began using high capacity, positive displacement oil pumps.
2. Subaru elected to create a new OEM oil filter, produced by Honeywell (owner of Fram at the time, with a horrible reputation no less), that would have specs to accommodate the oil pumps output.
3. Due to the limitations of oil filtration at the time Subaru elected to use a higher bypass spec to compensate for factors such as flow restrictive filter media, filter media with limited particulate capture capacity, filter media susceptible to damage due to higher pump flow capacity, lower media flow rate, stress from particulate saturation, etc.
4. Subaru, like every other auto manufacturer and parts supplier, took all factors into consideration and sought to mass produce the lowest cost oil filter that met the required specs.
Other factors to consider since model year 2009
A. Advancement in technology - oil filtration made huge strides immediately after the timeframe in which the higher bypass Subaru OEM oil filter was introduced. Royal Purple introduced an oil filter that used 100% synthetic media that allowed for a much higher flow rate AND capture capacity than any cellulose based filter media before it.
B. Fram was sold by Honeywell to Trico in January 2011 - this was a game changing business move. Fram went from producing horrible reputation products under Honeywell to producing the industry leading spin on can oil filter in the Ultra under Trico.
C. If Fram can produce an OEM oil filter for Subaru that meets bare minimum standards, do you really believe that their premium quality oil filter products cannot exceed those same bare minimum standards?
D. Are variables in all performance testing static? By that do I mean do the standards, methods, and materials used for product testing in 2009 have zero difference differences as compared to the current day? Was the SL or SM rated 5w30 oil used in 2009 testing no different and produced no different results than SN PLUS or SP rated 0w20 oil in 2020?
E. Is the oil filter a pressure choke point in an engine's oil lubrication system?
F. Is the path of least resistance for oil in an oil filter, with unsaturated filter media, the filter media or the bypass valve?
I do not buy into the bypass boogeyman.
Below is a thread from BITOG that speaks specially about the Fram Ultra XG7317 oil filter and there are helpful links in post #7 and #10 for more perspective."
Original post link:
www.subaruoutback.org
"The reality is, and I have daisy chained several threads together on BITOG in the past to substantiate this conclusion, that the bypass spec of Subaru's OEM oil filter what established due to a few factors:
1. In model year 2009 Subaru began using high capacity, positive displacement oil pumps.
2. Subaru elected to create a new OEM oil filter, produced by Honeywell (owner of Fram at the time, with a horrible reputation no less), that would have specs to accommodate the oil pumps output.
3. Due to the limitations of oil filtration at the time Subaru elected to use a higher bypass spec to compensate for factors such as flow restrictive filter media, filter media with limited particulate capture capacity, filter media susceptible to damage due to higher pump flow capacity, lower media flow rate, stress from particulate saturation, etc.
4. Subaru, like every other auto manufacturer and parts supplier, took all factors into consideration and sought to mass produce the lowest cost oil filter that met the required specs.
Other factors to consider since model year 2009
A. Advancement in technology - oil filtration made huge strides immediately after the timeframe in which the higher bypass Subaru OEM oil filter was introduced. Royal Purple introduced an oil filter that used 100% synthetic media that allowed for a much higher flow rate AND capture capacity than any cellulose based filter media before it.
B. Fram was sold by Honeywell to Trico in January 2011 - this was a game changing business move. Fram went from producing horrible reputation products under Honeywell to producing the industry leading spin on can oil filter in the Ultra under Trico.
C. If Fram can produce an OEM oil filter for Subaru that meets bare minimum standards, do you really believe that their premium quality oil filter products cannot exceed those same bare minimum standards?
D. Are variables in all performance testing static? By that do I mean do the standards, methods, and materials used for product testing in 2009 have zero difference differences as compared to the current day? Was the SL or SM rated 5w30 oil used in 2009 testing no different and produced no different results than SN PLUS or SP rated 0w20 oil in 2020?
E. Is the oil filter a pressure choke point in an engine's oil lubrication system?
F. Is the path of least resistance for oil in an oil filter, with unsaturated filter media, the filter media or the bypass valve?
I do not buy into the bypass boogeyman.
Below is a thread from BITOG that speaks specially about the Fram Ultra XG7317 oil filter and there are helpful links in post #7 and #10 for more perspective."
anyone can share FRAM XG7317's flow-delta p graph?
just wondering how it can take more then 13GPM oil volume. Thanks
www.bobistheoilguy.com
Original post link:
2020/21 Outback Oil Change SUPERTHREAD!
That said, we have a 2020 Limited, going on 3K miles. When is it advisable to go to Mobil1, or are there issues with M1? I have had it in all vehicles and does more than a great job from what I can tell, and is much more available / less pricey. That also said, I see the 2.5 states 4.4 quarts...
www.subaruoutback.org
From the same thread:
![Image]()
For hot thin oil I am sure that the Fram will never go into bypass based on the above chart.
Cold start is a reason why 0w oils should be used if you have a low bypass pressure oil filter. If you're using a 10w-30 then prolonged cold start bypass could be a problem.
Similarly if you're using a 0w-40 it might be an issue at high RPM in an engine designed for 0w-20.
So just to be clear, I'm not saying that the Fram Ultra is a bad or inappropriate filter. I'm just saying that you need to consider oil viscosity (temperature) as part of that decision.
For hot thin oil I am sure that the Fram will never go into bypass based on the above chart.
Cold start is a reason why 0w oils should be used if you have a low bypass pressure oil filter. If you're using a 10w-30 then prolonged cold start bypass could be a problem.
Similarly if you're using a 0w-40 it might be an issue at high RPM in an engine designed for 0w-20.
So just to be clear, I'm not saying that the Fram Ultra is a bad or inappropriate filter. I'm just saying that you need to consider oil viscosity (temperature) as part of that decision.
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Finally a good explanation and strait forward, after reading the GM report it states why and how important the Psi rating is.
There's an informative post on BITOG that explains when bypass might happen, for example if you rev the engine high when the oil is cold (thick).
Question about filter bypass.
Would it be a true statement that canister filters with a bypass, will generally go into bypass right after a cold start?
bobistheoilguy.com
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1 Posts
Been reading threads here and Bob the oil guy's site. I loathe buying the overpriced OEM filters (and the stupid crush washers that I've never had on any prior car...and I didn't even use one - didn't notice it on my first oil change (let stealership do the first two)). I found the crush washer in the dirty oil container! It seems fine w/o it (4000+ miles w/o it), LOL...
I used the Fram Utra out of dumb luck...was the best filter at Walmart is why I bought it - didn't know about the bypass controversy.
Hopefully most debris gets stuck in the media and wont flow upwards through the bypass valve...just wishful thinking.
We also have gravity on our side due to the filter being upside down (bypass valve is above the media and debris).
Our 2019 forester is parked in our garage, which rarely gets below 32 degrees...but on the way home, it can be below 20 degrees.
I've seen graphs in these threads of oil flow rate versus pressure drop, but it was for 5w-30 oil...not applicable/accurate for us.
With furnace filters, the ones which filter out smaller particles are more restrictive, so I use a cheaper less restrictive one.
Hopefully it's true that the better/synthetic oil filters can do both - filter finer particles, yet flow better.
If I lived down south, I wouldn't worry about the bypass spec...cold oil is much thicker - I surmise that's when it opens.
BTW, if you drain the oil out of your dirty oil container slowly, so the "debris" doesn't flow out, there is some metal in the used oil (I'm referring to my other vehicles - only have done one Forester change and can't recall if there was debris).
They were mostly the size of sand, but I've seen larger "chunks", and some rubber debris (2013 ford Focus)). Friend says his vehicles with 200k miles even have "debris", and to not worry...but I find it very surprising. I've wondered if the filter has more debris in it...you would hope so...and if the filter is working, why is there debris in my dirty oil!!! Oil in the used filter should drain through the filter after removal (maybe a tiny bit leaks through anti-drainback).
I used the Fram Utra out of dumb luck...was the best filter at Walmart is why I bought it - didn't know about the bypass controversy.
Hopefully most debris gets stuck in the media and wont flow upwards through the bypass valve...just wishful thinking.
We also have gravity on our side due to the filter being upside down (bypass valve is above the media and debris).
Our 2019 forester is parked in our garage, which rarely gets below 32 degrees...but on the way home, it can be below 20 degrees.
I've seen graphs in these threads of oil flow rate versus pressure drop, but it was for 5w-30 oil...not applicable/accurate for us.
With furnace filters, the ones which filter out smaller particles are more restrictive, so I use a cheaper less restrictive one.
Hopefully it's true that the better/synthetic oil filters can do both - filter finer particles, yet flow better.
If I lived down south, I wouldn't worry about the bypass spec...cold oil is much thicker - I surmise that's when it opens.
BTW, if you drain the oil out of your dirty oil container slowly, so the "debris" doesn't flow out, there is some metal in the used oil (I'm referring to my other vehicles - only have done one Forester change and can't recall if there was debris).
They were mostly the size of sand, but I've seen larger "chunks", and some rubber debris (2013 ford Focus)). Friend says his vehicles with 200k miles even have "debris", and to not worry...but I find it very surprising. I've wondered if the filter has more debris in it...you would hope so...and if the filter is working, why is there debris in my dirty oil!!! Oil in the used filter should drain through the filter after removal (maybe a tiny bit leaks through anti-drainback).
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21 Posts
Perhaps a reason that opinions are so varied is that the major companies keep changing their filters and in fact the manufacturer of the filters for each brand seems to not be a constant over any five year period, according to my mechanic.
My very experienced mechanic, specializing in Japanese cars, says he is always six months behind on his own opinions from observations, because he is always observing old oil. He also says he has cut up many filters and the quality of construction varies - but he cannot correlate the quality of construction to what he sees as a result [just not enough information, no constants, etc.]. So he suggests oil analysis for turbos and regular oil changes for everyone. He thinks WIX, Purolator's top line at any given time, M1, and Bosch have generally been well constructed and with lots of pleats and synthetic or part synthetic filtration - but he is not making recommendations because how those filters are actually made could change in a flash. He thinks the M1s changed recently - cheaper appearing construction.
On Subes, he says the blue filter is constructed very cheaply. He thinks that is no problem for a naturally aspirated Sube with synthetic changes at 5K mi and "normal" driving. IIRC, he thinks the Honda branded filter is crappily built, as well. He has leaned toward the WIX as his Sube turbo oil filter of choice unless the customer wanted something else, specifically. He doesn't think a filter within even 10K mi of normal driving in a non-turbo engine would ever see anything near a 20 psi drop across the filter. But he has added secondary filtration to raced WRXs and STIs.
Normal driving? He means no gunning a cold engine, plus a mix of highway and stop and go that includes at least one 25+ mi. trip each week. All short trips, or all stop and go, or raced, he suggests [much] more frequent changes. Gunning a cold engine will shorten its life no matter how often you change the oil or what filter is used.
This is probably acute insight into the obvious for most here, but I had not realized how many brands were manufactured by the same companies and how different the construction could be and how often they changed, so perhaps that is new for some of you as well.
My very experienced mechanic, specializing in Japanese cars, says he is always six months behind on his own opinions from observations, because he is always observing old oil. He also says he has cut up many filters and the quality of construction varies - but he cannot correlate the quality of construction to what he sees as a result [just not enough information, no constants, etc.]. So he suggests oil analysis for turbos and regular oil changes for everyone. He thinks WIX, Purolator's top line at any given time, M1, and Bosch have generally been well constructed and with lots of pleats and synthetic or part synthetic filtration - but he is not making recommendations because how those filters are actually made could change in a flash. He thinks the M1s changed recently - cheaper appearing construction.
On Subes, he says the blue filter is constructed very cheaply. He thinks that is no problem for a naturally aspirated Sube with synthetic changes at 5K mi and "normal" driving. IIRC, he thinks the Honda branded filter is crappily built, as well. He has leaned toward the WIX as his Sube turbo oil filter of choice unless the customer wanted something else, specifically. He doesn't think a filter within even 10K mi of normal driving in a non-turbo engine would ever see anything near a 20 psi drop across the filter. But he has added secondary filtration to raced WRXs and STIs.
Normal driving? He means no gunning a cold engine, plus a mix of highway and stop and go that includes at least one 25+ mi. trip each week. All short trips, or all stop and go, or raced, he suggests [much] more frequent changes. Gunning a cold engine will shorten its life no matter how often you change the oil or what filter is used.
This is probably acute insight into the obvious for most here, but I had not realized how many brands were manufactured by the same companies and how different the construction could be and how often they changed, so perhaps that is new for some of you as well.
Since our oil pumps are mechanical, flow is determined by engine RPM, not load, and Subaru oil pumps are higher flowing compared to most oil pumps. So high rpm even just revving the engine with no load will create a high pressure differential if the oil is cold and viscous.
While it's certainly best practice to fully warm up your car before going at high RPM, in reality it's very inconvenient to either sit at idle (not recommended) for extended periods of time, or to drive around the block slowly keeping engine RPM's low until the engine fully warms up (oil temps lag after water temps have reached normal range).
I live one block from a highway so I don't have miles of slow speed driving before I suddenly need to accelerate and RPMs will be high. On my car it takes about 5 miles or 10 minutes of driving before the oil is at 190 degrees or higher. That's why on my engine, I reach high RPM before the oil is fully warmed up, every time I drive it, and won't use an oil filter with a low bypass.
While it's certainly best practice to fully warm up your car before going at high RPM, in reality it's very inconvenient to either sit at idle (not recommended) for extended periods of time, or to drive around the block slowly keeping engine RPM's low until the engine fully warms up (oil temps lag after water temps have reached normal range).
I live one block from a highway so I don't have miles of slow speed driving before I suddenly need to accelerate and RPMs will be high. On my car it takes about 5 miles or 10 minutes of driving before the oil is at 190 degrees or higher. That's why on my engine, I reach high RPM before the oil is fully warmed up, every time I drive it, and won't use an oil filter with a low bypass.
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That is true for most of us, indeed. The closest to jackrabbit driving cold that comes to mind is merging onto a freeway just minutes from a cold start. An engine remanufacturer I have dealt with thinks that 3500 RPM is hugely preferable to 5500 RPM, cold, on a 6K RPM red line motor. 3500 RPM is probably enough to get on the freeway east of SoCal...
The pressure differential is across the filter from input pressure to output pressure. High pressure in ～ high pressure out, typically, except for a ridiculously clogged filter or sludge, if I understand the mechanics correctly. And the 0W20 oil should not sludge sitting overnight at ambient temperature in a garage in Austin, TX, but outside overnight in winter in the north I concede that the bypass could be a real issue.
So far I haven't heard of any oil filter related failures, high or low bypass so maybe aside from armchair discussions it doesn't make a real world difference. Still, given a choice, I'll stick with the Subaru specified bypass or something close to it. Also never heard of a failure of the "fiber" end-caps in the fram-manufactured Subaru blue filters either. Having said that, I prefer the synthetic Wix XP or Purolator Boss, and if I'm going to use cellulose I'd prefer the Tokyo Roki filter for Mazda, N3R1-14-302.
Similarly, laboratory studies show that engine wear is much less if you have very fine particulate filtration but I haven't heard of any subaru engine failures specifically because an oil filter with large pore size was used, although timing chain wear in a turbo direct injection engine is said to be caused by GDI soot in the oil - not sure if fine filtering media is fine enough to extract that, so to me, frequent oil changes are my method of fine particle removal.
Similarly, laboratory studies show that engine wear is much less if you have very fine particulate filtration but I haven't heard of any subaru engine failures specifically because an oil filter with large pore size was used, although timing chain wear in a turbo direct injection engine is said to be caused by GDI soot in the oil - not sure if fine filtering media is fine enough to extract that, so to me, frequent oil changes are my method of fine particle removal.
One of the reasons that filters such as M1 and Fram Ultra use a lower spec is because there is less resistance due to the higher effective surface area of the media. The flow is effectively greater for those filters. Even if you have to change the oil every 6K they are still worth getting because of their better filtration.
In any case, DI caused fuel dilution is probably going to be more of a concern than what kind of filter or oil that is used.
In any case, DI caused fuel dilution is probably going to be more of a concern than what kind of filter or oil that is used.
The low resistance media is low resistance when the oil is hot and thin, but when it's cold and thick it's still restrictive. If you go from ignition start to over 4000 RPM like I do in about 60 seconds (not best practice but it's where I live it's what I do daily) you don't want a low bypass filter.
Even if the filter is non-restrictive there's no technical reason why a lower than Subaru bypass would be better. In my opinion it's low simply so that it can be used in wider application where a high bypass would not meet specs. For example the exact same Fram Ultra with low 13 psi bypass pressure that fits the Outback also applies to my 2009 Honda Fit that expects low bypass pressure. Subaru oil pumps have higher volume than most.
![Image]()
Even if the filter is non-restrictive there's no technical reason why a lower than Subaru bypass would be better. In my opinion it's low simply so that it can be used in wider application where a high bypass would not meet specs. For example the exact same Fram Ultra with low 13 psi bypass pressure that fits the Outback also applies to my 2009 Honda Fit that expects low bypass pressure. Subaru oil pumps have higher volume than most.
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Subaru, Wix, and (wait for it) the Mazda N3R1-14-302. Although technically the Mazda bypass valve rating is 20.3 to 26.1 psi. The Mazda filter is also taller so you get the bonus of additional filtration media surface area.
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High flow filters are good if you are changing your oil a lot and don't expect any issues.
But lets say you have some sealant or some other large contaminant particulates circulating your system and/or maybe you are running higher temp oil because you shake your fist at all this 0w balderdash.
When you start the car up on a cold morning, if you have wildly different spec filter you are absolutely running the risk, every time, of your filter is just saying 'I'm not touching that ****', and stops doing its job when it absolutely should be.
But lets say you have some sealant or some other large contaminant particulates circulating your system and/or maybe you are running higher temp oil because you shake your fist at all this 0w balderdash.
When you start the car up on a cold morning, if you have wildly different spec filter you are absolutely running the risk, every time, of your filter is just saying 'I'm not touching that ****', and stops doing its job when it absolutely should be.
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That was then. Today there are more options (this is not an exhaustive list)
Tokyo Roki N3R1-14-302
Purolator Boss PBL14615
The Wix 57055 XP (and Wix made NAPA platinum 47055 and gold 7055 filters for Subaru)
The HENGST H345W is exclusively for Subaru boxer motors but the actual bypass spec isn't listed anywhere.
Tokyo Roki N3R1-14-302
Purolator Boss PBL14615
The Wix 57055 XP (and Wix made NAPA platinum 47055 and gold 7055 filters for Subaru)
The HENGST H345W is exclusively for Subaru boxer motors but the actual bypass spec isn't listed anywhere.
I don't know if it's temporary or for good, but I haven't been able to find a Wix 57055XP for a couple of months. Local stores are out, nothing at the national online outlets either.
I went into the nearby O'Reilly last week to see if they had the XP for my Mazda and they only had 6 or 7 part numbers total in XP filters. Makes me wonder if the whole product line is no longer produced.
I went into the nearby O'Reilly last week to see if they had the XP for my Mazda and they only had 6 or 7 part numbers total in XP filters. Makes me wonder if the whole product line is no longer produced.
I have also found difficulty finding Purolator Boss so I took a gamble on the Hengst filters which seem to be well made and dirt cheap.
Mann + Hummel owns both Purolator and Wix now.
The Wix XP is the same as NAPA Platinum oil filters - have you tried that?
Mann + Hummel owns both Purolator and Wix now.
The Wix XP is the same as NAPA Platinum oil filters - have you tried that?
The NAPA version shows out of stock online. At this point, I've lost interest in wasting more time going to more local stores to check. I've found that in-store stock rarely agrees with what the website says.
The Royal Purple filter is gone now, too.
I bought a couple of the Mazda Tokyo Roki filters. It doesn't seem like a huge ask to have proper bypass, quality construction, and a documented better-than-average filtration in a filter that's actually available. I could look at BITOG, but what a time sinkhole...
The Royal Purple filter is gone now, too.
I bought a couple of the Mazda Tokyo Roki filters. It doesn't seem like a huge ask to have proper bypass, quality construction, and a documented better-than-average filtration in a filter that's actually available. I could look at BITOG, but what a time sinkhole...
IIRC there was some talk on BITOG about the Napa Platinum and WIX XP potentially being unavailable a while ago.
Speaking of O'Reilly Auto Parts, they carry the Microguard Select MSL 57055 which uses a Subaru approved bypass spec. I used one of these during my last oil change interval and it worked great. I cut it open afterwards and it was in perfect condition internally with excellent construction. It will be my go to oil filter from now on.
FYI...stilll noodling about Subaru's unusually high oil filter bypass spec of 23.2psi. Have not obtained from Subaru dealer or Subaru national any information about why that spec or whether or not it's important. Have continued to wonder about the issue while considering better-filtering after-market offerings all of which have lower psi spec. Responses from Fram, Wix, Amsoil, Mobil have been boilerplate. Inquired and received these responses from Purolator about their Boss filter and they responded quickly with mo/betta information than have the others. Here's the e-mail exchange......
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