Conclusion of the Subaru bypass pressure thread

[supercity]

Hi

I started out reading the Subaru Oil Pump Specs as Relates to Filter Bypass thread, and I got lost around page 3. I am interested to know what the overall conclusion was or what the apposing views were.

If matching up an aftermarket filter would you stick with the OEM by-pass pressure or will it make little difference?

I ask as one of my cars also has a 23psi bypass valve. I have noticed some filter manufacturers list a filter with the 23psi bypass pressure and also offer an alternative filter with a different pressure valve. One manufacturer lists a much larger filter with a lower bypass pressure. I'm guessing it must be able to cope with a higher flow rate so the bypass valve can afford to be set lower. Is this thinking correct?

 

[y_p_w]

I don't believe flow rate is really so much the issue as whether or not the filter is heavily loaded enough to force the bypass.

As far as I know, the Wix 57712 is the only aftermarket filter with the 23 psi bypass pressure. Maybe some of the OEM copies from Beck-Arnley, Full, or NPN, but those specs aren't available.

 

[ZeeOSix]

Originally Posted By: y_p_w
I don't believe flow rate is really so much the issue as whether or not the filter is heavily loaded enough to force the bypass.


The flow rate has a lot to do with it because with increased oil flow rate, the delta-p across the media increases which means you would need a higher bypass valve setting to prevent unwanted bypassing.

Look at the oil volume output on those Subaru engines ... it's massive. Not your ordinary car on the street.

@5000 rpm: Discharge pressure 43psi; Discharge rate 49.7 US quarts or more per minute ... that's 12.4 GPM.

Many of the aftermarket oil filter makers spec a filter with a higher bypass setting, most likely due to the high volume oil pumps on these engines.

 

[ZeeOSix]

Originally Posted By: supercity

I ask as one of my cars also has a 23psi bypass valve. I have noticed some filter manufacturers list a filter with the 23psi bypass pressure and also offer an alternative filter with a different pressure valve. One manufacturer lists a much larger filter with a lower bypass pressure. I'm guessing it must be able to cope with a higher flow rate so the bypass valve can afford to be set lower. Is this thinking correct?


That is correct. If you look at the media area on the Subaru OEM filter, it's listed (in that other long thread) at 124 sq-in. As the same media type's area increases, the delta-p goes down if flowing the same oil volume through it. So in turn, the bypass valve setting can also be lowered.

If a filter manufacturer lists a filter specifically for that engine with the high volume oil pump, and the bypass valve setting is lower than the OEM filter, then that's what's going on - the filter's design has also played a factor in the bypass valve setting. The aftermarket filter either has more media, and/or the media doesn't develop as much delta-p under the same use conditions (ie, it "flows better").

 

[ARCOgraphite]

Caution that unimpeded pump flow rate is not necessarily equal to the rate through the engine mains. Fuji had issues in the past with turbo oiler banjo fitting filter screens plugging, and in high performance driving scenario Fuji may wish to minimize bypassed (unfiltered) oil heading to the turbo bearings.

Possibly, our resident Suburu expert Bluesubie could comment.

 

[ZeeOSix]

Originally Posted By: ARCOgraphite
Caution that unimpeded pump flow rate is not necessarily equal to the rate through the engine mains. Fuji had issues in the past with turbo oiler banjo fitting filter screens plugging, and in high performance driving scenario Fuji may wish to minimize bypassed (unfiltered) oil heading to the turbo bearings.


So sounds like the oil going to the turbo and hitting this banjo fitting screen was not oil that was just previously filtered by the oil filter? Why would this screen that is able to pass much larger particles than the oil filter clogging up?

 

[SlipperyPete]

The recommended filters from Fram for a 2001 4 cyl, for example, show a 12 psi bypass. Would they probably be OK to use?

 

[ZeeOSix]

Originally Posted By: SlipperyPete
The recommended filters from Fram for a 2001 4 cyl, for example, show a 12 psi bypass. Would they probably be OK to use?


If that's the filter they specify, then I'd assume it's OK.

Might not hurt to email Fram and have them check with their engineers to verify they know about the Subaru's high volume oil pump and have considered that in their specified filter.

 

[flstffxe]

Originally Posted By: ZeeOSix
Originally Posted By: SlipperyPete
The recommended filters from Fram for a 2001 4 cyl, for example, show a 12 psi bypass. Would they probably be OK to use?


If that's the filter they specify, then I'd assume it's OK.

Might not hurt to email Fram and have them check with their engineers to verify they know about the Subaru's high volume oil pump and have considered that in their specified filter.


They are aware. Honeywell, now makes the OEM service filter SOA# 15208AA12A.

Fram now specs a PH9715 for most all Subaru EJ applications. 22PSI valve +/- 4PSID

Quote:
PH9715 Recommendation based on current original equipment requirements.

 

[cptbarkey]

my conclusion is it doesn't matter squat. that thread is OCD's galore. I am working on my 3rd rebuilt subaru and they start off with cheap napa silvers to catch the RTV and loose partciles, and then I have a small hoard of OEM subaru filters (fram) that they then receive. theeeee end.

 

[ZeeOSix]

Originally Posted By: cptbarkey
my conclusion is it doesn't matter squat. that thread is OCD's galore. I am working on my 3rd rebuilt subaru and they start off with cheap napa silvers to catch the RTV and loose partciles, and then I have a small hoard of OEM subaru filters (fram) that they then receive. theeeee end.


But you are primary using OEM Subaru filters, so of course there should be no concern. The thread might be OCD to some degree (it's a classic

), and I can see whey some are concerned.

My recommendation is to always use an oil filter that is clearly specified for the Subaru vehicle in question ... then if some kind of oil filter related engine failure occurs, you have a change of getting warranty coverage from the aftermarket filter maker.

 

[SubLGT]

Here is an interesting read:

http://forums.nasioc.com/forums/showthread.php?t=2301839&highlight=filter

 

[ZeeOSix]

Originally Posted By: SubLGT
Here is an interesting read:

http://forums.nasioc.com/forums/showthread.php?t=2301839&highlight=filter


Did you see the comment in Post #45 ...
"Be careful with BITOG, there are lots of people who think they know what they're talking about."

...

In Post #47 he says:
"My very simple point is that Subaru prioritizes flow over filtration, so if we're picking an aftermarket filter, flow should be a priority. None of the aftermarket manufacturers provide detailed flow data."

If Subaru "prioritized flow over filtration" in their OEM filters, then the filter bypass setting wouldn't be at 23+ PSI (it would be less) because the filter wouldn't be producing so much delta-p across the media if it was a very "free flower" ... even with the high volume oil pump these engines have.

I believe the bypass setting on these Subaru filters is because they do filter relatively decent, and they do have a pretty good delta-p across the media at the high oil flow rates ... therefore, Subaru had to set the bypass valve to a pretty high setting to ensure the filter wouldn't go into bypass too often.