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#1410171 - 03/21/09 10:51 AM Subaru Oil Pump Specs as Relates to Filter Bypass
LoneRanger Offline


Registered: 07/02/07
Posts: 1582
Loc: Midwest
It was asked a while back what the numbers were on the Subaru oil pump, during discussion regarding the 23psi bypass pressure setting in the Subaru OE oil filter, as we were trying to figure out why the bypass pressure spec was set so high. So here are the specs on the oil pump, to possibily help understand why the filter bypass rating is set @ 23psi (23.2 actually)

Oil Pump info for 2009 Subaru 2.5 liter four cylinder(identical specs for Turbo DOHC and NA SOHC 2.5 liter motors):


Lubrication Method: Forced lubrication
Pump Type: Trochoid type

Performance (oil temp 80 C which is 176 F)

600rpm: Discharge Pressure 14psi; Discharge rate 4.9 US quarts or more per minute

5000rpm: Discharge pressure 43psi; Discharge rate 49.7 US quarts or more per minute

Relief Valve working pressure: 85psi

Oil Filter

Type: Full Flow
Filtration Area: 124 sq in (800 sq cm)
Bypass Valve opening pressure: 23.2psi
Outer diameter x width: 2.68 x 2.56 in (68 x 65mm)
Installation screw specifications: M 20 x 1.5

Oil Pressure Switch warning light operating pressure: 2.1 psi
Oil Pressure Switch proof pressure: 142 psi


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'13 Ducati MTS .......... (Silkolene Pro 4 Ester 15W50)

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#1410273 - 03/21/09 12:39 PM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: LoneRanger]
Gary Allan Offline


Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
Maybe Superbusa will have a séance with Bernelli for his insight into it.


(yes, I'm waiting )
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#1410289 - 03/21/09 12:59 PM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: Gary Allan]
SuperBusa Offline


Registered: 03/01/09
Posts: 2371
Loc: WA
 Originally Posted By: Gary Allan
Maybe Superbusa will have a séance with Bernelli for his insight into it.


(yes, I'm waiting )


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#1410303 - 03/21/09 01:14 PM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: SuperBusa]
Gary Allan Offline


Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
Refresh me, LoneRanger ..does this have a gauge or an idgit light ..and does the turbo get the same pump (which I think comes with a guage)?
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#1410305 - 03/21/09 01:15 PM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: LoneRanger]
SuperBusa Offline


Registered: 03/01/09
Posts: 2371
Loc: WA
 Originally Posted By: LoneRanger

Oil Pump info for 2009 Subaru 2.5 liter four cylinder(identical specs for Turbo DOHC and NA SOHC 2.5 liter motors):


Lubrication Method: Forced lubrication
Pump Type: Trochoid type

Performance (oil temp 80 C which is 176 F)

600rpm: Discharge Pressure 14psi; Discharge rate 4.9 US quarts or more per minute

5000rpm: Discharge pressure 43psi; Discharge rate 49.7 US quarts or more per minute


Relief Valve working pressure: 85psi



Wow ... you got all the detailed specs there.

Looking at the oil pumps output volume - 49.7 qts/min = 12.4 GPM - that's A LOT of oil flow. And that's at 43 psi discharge pressure, which means it can put out that much flow before it's pressure relief valve opens at 85 psi.

IMO, the filter's bypass is set higher because of the high volume oil pump. See chart below - you can see for these typical filters that at 6~8 GPM with COLD oil there is a huge PSID - 45 to 50 psi differential across the element. Of course with hot oil this will come way down.



So, it does look like the Subaru really needs a filer with a high bypass setting in order to ensure less time that the filter is in bypass mode. Obviously, this is more critical when the oil is cold with higher engine RPM. When the oil is near or at full operating temperature I'm sure the 23 psi bypass filter would never or hardly ever be in bypass. But, if you used a filter with a lower bypass there would certainly be more time in bypass mode IMO when the oil was cold and in the warm-up stage ... maybe even possibly when the oil is hot at max engine RPM.

Seems some of the bigger filter manufacture's like WIX or Purolator would come out with a filter with the high bypass setting for these Subarus ... as the filter manufactures are supposed to design their filters based on the vehicle's oil system specs.

No Bernoulli needed just yet.
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#1410369 - 03/21/09 02:49 PM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: SuperBusa]
Gary Allan Offline


Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
 Quote:
Looking at the oil pumps output volume - 49.7 qts/min = 12.4 GPM - that's A LOT of oil flow. And that's at 43 psi discharge pressure, which means it can put out that much flow before it's pressure relief valve opens at 85 psi.


hmmm..cold flow and 45lb of differential? That would be only possible if less than half of the output (at whatever output the oil pump was producing) reached the engine @ 85lb. Which cannot occur if the pump is not in relief. We'll, for the moment, assume that the media could withstand 45lb PSID and had no bypass.

Call Bernelli.
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#1410427 - 03/21/09 04:27 PM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: Gary Allan]
LoneRanger Offline


Registered: 07/02/07
Posts: 1582
Loc: Midwest
 Originally Posted By: Gary Allan
Refresh me, LoneRanger ..does this have a gauge or an idgit light ..and does the turbo get the same pump (which I think comes with a guage)?


Idiot light on mine, mine being the base trim non-turbo. Yes, beginning in model year 2006 both the turbo and non-turbo got the same oil pump with same specs, same filter specs as well.

Before model yr 2006 the specs as posted above were only for the turbo motor, the pressure specs were same for the non-turbo but the volume was a bit less... 3.4 US qts/minute @ 600rpm and 34.4 US qts/minute @ 5000rpm and Relief Valve Pressure was 71psi for the non-turbo motor. Filter bypass at that time was still 23.2psi though.
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'09 Subaru Forester .. (Kendall GT-1 Syn Blend 5W30)
'13 Ducati MTS .......... (Silkolene Pro 4 Ester 15W50)

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#1410433 - 03/21/09 04:34 PM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: SuperBusa]
LoneRanger Offline


Registered: 07/02/07
Posts: 1582
Loc: Midwest
 Originally Posted By: SuperBusa

Wow ... you got all the detailed specs there.


Yup. From the 2009 Forester factory service manual. :~)
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'13 Ducati MTS .......... (Silkolene Pro 4 Ester 15W50)

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#1410803 - 03/21/09 11:32 PM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: LoneRanger]
SuperBusa Offline


Registered: 03/01/09
Posts: 2371
Loc: WA
 Originally Posted By: Gary Allan
 Quote:
Looking at the oil pumps output volume - 49.7 qts/min = 12.4 GPM - that's A LOT of oil flow. And that's at 43 psi discharge pressure, which means it can put out that much flow before it's pressure relief valve opens at 85 psi.


hmmm..cold flow and 45lb of differential? That would be only possible if less than half of the output (at whatever output the oil pump was producing) reached the engine @ 85lb. Which cannot occur if the pump is not in relief. We'll, for the moment, assume that the media could withstand 45lb PSID and had no bypass.

Call Bernelli.


Not quite what I meant. This is kind of long and drawn out to get the whole point across ... so hang in there.

Let’s look at those oil pump specs again:

 Quote:
Pump Type: Trochoid type
Performance (oil temp 80 C which is 176 F)
5000rpm: Discharge pressure 43psi; Discharge rate 49.7 US quarts or more per minute
Relief Valve working pressure: 85psi


Imagine that the engine is running at a constant 5000 RPM, and the oil temp is 176 deg F. The oil pump will be putting out 49.7 qts/min (12.4 gpm) at an output pressure of 43 psi. Remember that the engine in this example is always running at 5000 RPM and never changes.

Now imagine that the oil is slowly cooled down … making the oil viscosity correspondingly thicker (higher density). The oil pump will keep putting out 12.4 gpm, but as the oil temp starts to decrease the pump’s output pressure will start to increase in order to keep the 12.4 gpm flowing.

Now imagine that the oil temperature is at yet a some cooler temperature – let’s assume the oil temperature is 100 deg F. The pump output pressure is now 84.9 psi … just at the verge of the pump to start pressure relieving. At this point, the pump is still putting out 12.4 gpm since the pump is still not in relief mode.

So, at this point, if the oil filter develops a PSID greater than its bypass setting, then it will also start to bypass. If the filter's bypass pressure was set to low for this engine, it's entirely possible that it could go into bypass with relatively warm oil since the pump's output is so high volume - much higher than most normal cars IMO.

Now imagine the oil temperature is starting to cool down once again from the 100 deg F point, with the engine still running at 5000 RPM. As the oil becomes cooler and cooler, more and more of the 12.4 gpm output gets spit back into the engine’s sump by the pump's relief vavle, and less flow goes to the filter/engine circuit. But, keep in mind that the viscosity is continually becoming greater as the oil temperature decreases.

Here’s the key … even though the flow rate going through the filter/engine circuit is becoming less and less as the oil cools down, the PSID is also coming down some due to less volume flow, but the PSID is not coming down very fast due to increase in oil viscosity factor … they cancel each other out to some degree.

So … lets assume that when the oil is cold (say 34 deg F) like shown in the chart below, that the oil pump is sending 4 gpm to the filter/engine oil circuit. Also assume that the filter being used has the same flow vs PSID performance curve as the black line (Fram Doubleguard) and has a bypass valve setting of 23 psi for the Subaru.



Well, you can see that in this case, there is a PSID of 23 psi across the filter, so it would be right at the verge of going into bypass mode.

Now assume you put another filter on the Subaru that had a bypass setting of 10 psi. In this case, the filter would have went into bypass at 10 PSID. Looking at the flow graph, this means that ~2.3 gpm will be going through the filter element, and the other 1.7 gpm will be bypassing the filter element to achieve the 4 gpm going to the system.

Obviously Subaru has specified a filter bypass valve setting higher than most engine manufactures because the oil pump is pretty high volume. Any oil pump that puts out 12.4 gpm at 5000 engine RPM at 43 psi discharge pressure also means the oiling system on those engines are not very restrictive, and Subaru wants to feed lots of oil volume to their engines for some reason.

Personally, I would not run any filter that doesn’t have the 23 psi bypass valve on this car … otherwise there could a lot more bypass action while the oil is cold and in the warm-up transition.

Bernoulli not required, and is out riding his Benelli, and unavailable at this time.


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#1410840 - 03/22/09 12:33 AM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: SuperBusa]
Gary Allan Offline


Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
 Quote:
Now imagine that the oil is slowly cooled down … making the oil viscosity correspondingly thicker (higher density). The oil pump will keep putting out 12.4 gpm, but as the oil temp starts to decrease the pump’s output pressure will start to increase in order to keep the 12.4 gpm flowing.


Yep. Someone inside the pump said "call down to the boiler room for more steam" ..our 12.4 gpm of throughput is cooling and we have to keep up! Steady as she goes!"


Something is unright about these spec's. The 43psi is not correct. Especially @ 12.4gpm @ 176F.

Ask a turbo owner what the typical pressures are at full op at much lower rpm.


but you've morphed a few things here into non-clarity

 Quote:
Remember that the engine in this example is always running at 5000 RPM and never changes.
 Quote:
let’s assume the oil temperature is 100 deg F. The pump output pressure is now 84.9 psi … just at the verge of the pump to start pressure relieving. At this point, the pump is still putting out 12.4 gpm since the pump is still not in relief mode.


Actually, if stuff was in some rational proportion, this would work out to about 70lb by there figures. It may not really work out that way ..but for "what if" ..we'll go with what you've got there. Still that number is not right.

 Quote:
But, keep in mind that the viscosity is continually becoming greater as the oil temperature decreases.


So ..we can say that our pump called down to the engine room for more steam ..they said "no way, man. We're at our limits! You'll have to vent to atmosphere or we're gonna blow!"

 Quote:
Here’s the key … even though the flow rate going through the filter/engine circuit is becoming less and less as the oil cools down, the PSID is also coming down some due to less volume flow, but the PSID is not coming down very fast due to increase in oil viscosity factor … they cancel each other out to some degree.


Here's the flaw and the key. The pressure seen by the media is (for the moment, it can be exceeded) is 85psi. The engine, seeing that same reduced flow over its restriction, is dissipating less pressure to move whatever volume is being passed through it. THAT produces your differential. The mismatch in that output produced and output realized.

Now in your scenario you've kept the volume extremely high to kick in the absolute impedance of the filter. Still the numbers can't be right. That peak pressure at 12.4 @ 176F is not correct.
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#1410856 - 03/22/09 12:54 AM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: Gary Allan]
SuperBusa Offline


Registered: 03/01/09
Posts: 2371
Loc: WA
 Originally Posted By: Gary Allan
Something is unright about these spec's. The 43psi is not correct. Especially @ 12.4gpm @ 176F.

Ask a turbo owner what the typical pressures are at full op at much lower rpm.


Those are the quoted specs from the Subaru shop manual. I'm assuming they are accurate at this point. One turbo does not define all turbos or other oil system designs. Spec are specs.


 Originally Posted By: Gary Allan
but you've morphed a few things here into non-clarity

 Quote:
Remember that the engine in this example is always running at 5000 RPM and never changes.
 Quote:
let’s assume the oil temperature is 100 deg F. The pump output pressure is now 84.9 psi … just at the verge of the pump to start pressure relieving. At this point, the pump is still putting out 12.4 gpm since the pump is still not in relief mode.


Actually, if stuff was in some rational proportion, this would work out to about 70lb by there figures. It may not really work out that way ..but for "what if" ..we'll go with what you've got there. Still that number is not right.


Keep in mind I'm not trying to predict exact numbers here ... I'm using numbers to show by example what's going on in the system as parameters change.


 Originally Posted By: Gary Allan
 Quote:
Here’s the key … even though the flow rate going through the filter/engine circuit is becoming less and less as the oil cools down, the PSID is also coming down some due to less volume flow, but the PSID is not coming down very fast due to increase in oil viscosity factor … they cancel each other out to some degree.


Here's the flaw and the key. The pressure seen by the media is (for the moment, it can be exceeded) is 85psi. The engine, seeing that same reduced flow over its restriction, is dissipating less pressure to move whatever volume is being passed through it. THAT produces your differential. The mismatch in that output produced and output realized.


Yes, the pressure seen by the filter input is 85 psi when the pump is in relief mode. The delta P across the filter is always going to be proportional to the oil flow volume & viscosity going through it ... a relationship like shown in that "Flow vs PSID" graph posted up earlier in this thread.

So, whatever volume and viscosity of oil that the 85 psi pump pressure can push through the fixed resistance circuit (defined by the filter + engine), will determine the exact volume of oil pushed through the circuit. The PSID across the filter will be determined by the flow rate and viscosity of the oil, and if that PSID is greater than the filter's bypass setting, then the filter will bypass. That's basically what I showed in the previous examples.

So, again ... if an engine has an oil pump with a very high volume output to the filter, that filter better be able to take the larger PSID across the element, and also have a bypass valve set accordingly to prevent unwanted bypass events. Simple as that.

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#1410860 - 03/22/09 01:10 AM Re: Subaru Oil Pump Specs as Relates to Filter Byp [Re: Gary Allan]
edhackett Offline


Registered: 06/09/03
Posts: 1572
Loc: Sequim, WA
LoneRanger, does the manual give the part number for the oil filter? The specifications say 124 sq. in. of filter area. I just measured the FRAM and came up with 65 sq. in. (depth of pleat x 2 x number of pleats x width of filter media).

The oversize filter such as the Wix 15356 that you are using and the Purolator PL14610 have ~130 sq. in. of media. The old AA080 Subaru filter (PL14460 size) was probably ~124 sq.in. of media.

This begs the question, would doubling the filter area balance the by-pass events? Would 65 sq. in. at 23 psi vs 130 sq. in. at 12 psi be the same?

Ed
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#1410864 - 03/22/09 01:13 AM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: SuperBusa]
Gary Allan Offline


Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
 Quote:
The PSID across the filter will be determined by the flow rate and viscosity of the oil, and if that PSID is greater than the filter's bypass setting, then the filter will bypass. That's basically what I showed in the previous examples.


No it won't. Now in this example, the scenario is manipulated to make it so. You're actually challenging the throughput limits of the filter. Outside of that constructed scenario, it's not so.

Outside of this impedance (effectively a reactive component that takes over beyond a given volume that will have some visc/volume sliding convertibility) the filter doesn't appear this way.

 Quote:
Those are the quoted specs from the Subaru shop manual. I'm assuming they are accurate at this point. One turbo does not define all turbos or other oil system designs. Spec are specs.

For the time being, you've got the shield of documented impunity ..but I'd say that you really are stretching your imagination on the plausibility of this being so.


I haven't quite picked apart everything here ..but you're still left with all the pressures adding up to supply. In one of your manipulations, it appears that you put the filter at parity with the engine with 1/2 of all pressure produced/dissipated over/by the filter.
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#1411041 - 03/22/09 09:33 AM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: Gary Allan]
LoneRanger Offline


Registered: 07/02/07
Posts: 1582
Loc: Midwest
Subaru offers a Technical Information System web site, http://techinfo.subaru.com/html/index.jsp where you can buy a subscription in varying durations and during the duration you have access to the Service Manual as PDF files, TSB's as PDF files, Tech Tips monthly bulletins, Campaigns (recalls) as PDF's, etc. Model years from 1990 - 2009.

I bought a 72 hr subscription for $34.95 and am in the process of downloading the entire service manual. But they have every little system as a separate PDF for instance the Oil Pump Specs, which means there are a ton of PDF's to download to get the entire Service Manaul-- they limit you to 50 file downloads per hour, when you hit #51 you get a notification that you have to wait x number of minutes before you can download more. I've got about 3/4 of the manual so far, I have Body Section, Wiring System Section, and Body Repair Manual left to get.

It is tedious and time consuming but a factory service manual I can burn to CD for $34.95 I guess it is worth the time consuming effort, lol.

That is where the oil pump specs came from, straight out of the Engine Section- Lubrication section. It does not tell a p/n for the filter on the oil pump spec sheet, just dimensions and specs of the filter.
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#1411280 - 03/22/09 02:43 PM Re: Subaru Oil Pump Specs as Relates to Filter Bypass [Re: Gary Allan]
SuperBusa Offline


Registered: 03/01/09
Posts: 2371
Loc: WA
 Originally Posted By: Gary Allan
 Quote:
The PSID across the filter will be determined by the flow rate and viscosity of the oil, and if that PSID is greater than the filter's bypass setting, then the filter will bypass. That's basically what I showed in the previous examples.


No it won't. Now in this example, the scenario is manipulated to make it so. You're actually challenging the throughput limits of the filter. Outside of that constructed scenario, it's not so.

Outside of this impedance (effectively a reactive component that takes over beyond a given volume that will have some visc/volume sliding convertibility) the filter doesn't appear this way.


Sure it will. What do you think causes the actual pressure drop across an oil filter? ... or any other fluid flow restriction? Flow through an oil filter causes a pressure drop across it. The volume and viscosity of the flow through any filter will develop a pressure drop proportional to the actual flow resistance characteristics of the filter assembly. This includes the filter element, as well as the base inlet holes and the center core outlet holes. They all play a part in the resistance of the filer assembly.

Why do you think manufacture's put a bypass valve in the filers? ... because they KNOW that at some point there will be a large enough PSID across the element to warrant bypassing the flow to keep the PSID to a maximum level. If a filter didn't have any possibility of producing a high PSID then they wouldn't need a bypass valve.

Why do you think Subaru has such a high filter bypass setting? IMO, it's because the oil pump on that engine has a very high volume output compared to many other cars on the road 12.4 gpm is ALOT of volume. They know that with more flow going through the filter that there will be a higher PSID across the filter, and have set the bypass higher to account for this. This gives more bypass "reserve headroom" for filter loading during its use period. If they put the bypass setting lower, then it may not take much filter loading to get its flow resistance higher, and will certainly cut the headroom down for those cold oil flow scenarios.

 Originally Posted By: Gary Allan
 Quote:
Those are the quoted specs from the Subaru shop manual. I'm assuming they are accurate at this point. One turbo does not define all turbos or other oil system designs. Spec are specs.

For the time being, you've got the shield of documented impunity ..but I'd say that you really are stretching your imagination on the plausibility of this being so.

I haven't quite picked apart everything here ..but you're still left with all the pressures adding up to supply. In one of your manipulations, it appears that you put the filter at parity with the engine with 1/2 of all pressure produced/dissipated over/by the filter.


I believe those specs from Subaru. I highly doubt they have an error in them. Until proven otherwise (like a TSB or similar from Subaru) saying there was an error in the shop manual, then those are the specs, and considered accurate.

Yes, I agree that the supply pressure must add up to the total amount of pressure lost through the system as it flows from inlet to outlet (outlet is zero psi - ATM pressure of the sump). BUT, keep in mind that an oiling system that is designed to flow 12.4 gpm of 176 deg F oil at 43 psi is a pretty wide open oiling system. This thing flows like mad ... and hence, the pressure drop across the engine circuit also has to be MUCH LOWER than your everyday vehicle with low volume pumps that only flow probably 1/3 or 1/4 of this Subaru system.

You need to look at what the Subaru system IS, instead of trying to think it must by like all the other systems out there. It's apples to oranges ... why else would Subaru have a bypass setting that is essentially DOUBLE the average bypass setting on 99+% of all other vehicles.
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