Oem bypass rating '13 outback 2.5i

[gpshumway]

The 12.4 GPM is at a rated ~45 PSI, the pressure relief valve is set at 85 PSI and the pump is a "trochoid" type (gerotor) positive displacement pump. Flow from such a pump is relatively insensitive to pressure, so as long as the pressure is below the relief valve pressure the flow will be very close to the rated 12.4 GPM. You'd have to be using 50wt or thicker oil for the pressure relief valve to be open at operating temp at 5,000 RPM.

So, no, the flow is not substantially less than 12 GPM with 5w30 oil at operating temp.

 

[ZeeOSix]

Originally Posted By: gpshumway
The 12.4 GPM is at a rated ~45 PSI ...


Is that spec right out of the factory service manual? Was there an oil weight and temperature (or viscosity) also listed? That amount of low with only 45 psi tells me it must be hot and pretty low in viscosity.

If so, then it does sound like that is the flow rate through the engine when there is 45 psi of oil pressure pushing flow through the oiling system.

 

[Jim Allen]

Doesn't sound right to me in light of below and it being a 2.5L engine. But I honestly don't know. If possible, sacn the specs page you got the info from incase there is a contextual problem.

Oil flow thru a 6.0L Powerstroke diesel, turbocharged with HUEI no less, is 18.5 GPM @ 3300 rpm hot oil

Oil Flow thru the later 6.4L Powerstroke turbo diesel, again with HUEI, is 13 GPM @ 3000 rpm

 

[ZeeOSix]

I guess I can believe the Subaru oil flow spec. Seems most hi-pro engines will flow around 10~12 GPM with hot oil.

 

[gpshumway]

Originally Posted By: ZeeOSix
Originally Posted By: gpshumway
The 12.4 GPM is at a rated ~45 PSI ...


Is that spec right out of the factory service manual? Was there an oil weight and temperature (or viscosity) also listed? That amount of low with only 45 psi tells me it must be hot and pretty low in viscosity.

If so, then it does sound like that is the flow rate through the engine when there is 45 psi of oil pressure pushing flow through the oiling system.


Yep, straight out of the FSM. I don't have it in front of me, but I believe it says operating temp and lists the 45 PSI as a minimum, which implies 5w30 oil as that's the thinnest oil recommended for this engine.

I don't think you're quite understanding the concept of a positive displacement pump though. Pressure does not drive flow in a hydraulic system with a positive displacement pump. You're thinking of pumps like the centripetal vane pumps used in cooling systems. As long as the system pressure is below the cracking pressure of the pressure relief valve, the only variation of flow with pressure is due to internal leakage through the pump, and is quite a small factor.

Take a look through the Nippon oil pump catalog linked below and see the variation in flow for different pressures at constant RPM, the curves are nearly flat. These pumps are electrically driven hydraulic system pumps, so they don't spin the kind of RPM an engine oil pump does, but their design is the same.
www.tjsolution.com/Nippon-Oil-Pump/Trochoid%20Pump_catalogue.pdf

Day 1 minute 1 of my industrial hydraulics class: Pumps create flow, resistance (orifi) creates pressure.

 

[ZeeOSix]

Originally Posted By: gpshumway

I don't think you're quite understanding the concept of a positive displacement pump though. Pressure does not drive flow in a hydraulic system with a positive displacement pump. You're thinking of pumps like the centripetal vane pumps used in cooling systems. As long as the system pressure is below the cracking pressure of the pressure relief valve, the only variation of flow with pressure is due to internal leakage through the pump, and is quite a small factor.


Don't know what I said that makes you think that (?) - please point out what has lead you to think I don't understand PD pumps. If you read any of my posts over the last 2~3 years when I talk about positive displacement oil pumps, you would see I do fully understand them.

Yes, I know "pressure doesn't drive flow" in a PD pump system. The "pressure" is the result of the PD pump forcing the oil down a path of resistance. With a constant volumetric output, if no resistance, no pressure ... lots of resistance and lots of pressure is the result. The pressure will also change as viscosity or flow resistance changes while holding the volume constant. Not rocket science.

Here's a graph I posted in another thread showing the oil pressure vs engine RPM on my Z06.



The slight knee over of the curve is probably due to slightly increasing internal leakage within the pump as pressure builds due to more and more volume being forced down the oiling system as engine RPM increases. You can see when the pump's pressure relief valve kicks in at 70 PSI.

 

[gpshumway]

Originally Posted By: ZeeOSix
Don't know what I said that makes you think that (?) - please point out what has lead you to think I don't understand PD pumps.


My apologies if you think I'm being condescending, I'm basing my assessment on your third most recent post in this thread:

Originally Posted By: ZeeOSix
The unknown about these oil pump flow specs ... is that with no restriction of the engine on the pump's outlet, or is that the actual flow going through the engine's oiling system? If it's just the output of the oil pump without the restriction of the oiling system, then the actual flow through the engine could be less.


From this post it sounded to me like you thought placing a restriction on the outlet of the pump would have a substantial impact on flow. I also read your second most recent post a little too quickly and that mis-read reinforced my impression.

At any rate, here's a screen-grab of the FSM. My recollection was incorrect, it doesn't state minimum pressure, but it does state an explicit oil temperature, though no oil weight. Oil at 80*C. Oil filter specs are in this screen grab as well. This FSM is obviously for my 2007 EJ255 engine and also applies to the EJ257 (sti) and the regular N/A 2.5l Impreza from 2007, but may not be relevant to the FB25 N/A engine in a 2013 Outback/Legacy.

 

[Jim Allen]

Interesting spec sheet. No manual for any of my equipment has that much detail, so thumbs up to Subaru!

At the risk of coming across intransigent, it doesn't clearly say whether that is just the flow of the pump without any restriction at the outlet or the total amount of flow going thru the engine. I'm just gobsmacked that such a small engine can have so much oil flow. And the fact that the spec'ed oil filters have so little flow reserve.... something which sets of alarms to be and makes me wonder if the 12.4 GPM is correct. This isn't a hill I will die on because I don't have much info here to counter it.

 

[gpshumway]

It seems to be an Asian thing. The manual for my Civic contains similar info for both the 1.8l engine in my car and the high performance 2.0l in the Civic Si. Both those engines specify similar flow rates to the Subaru. If you extrapolate the Honda K20Z3 (2.0l) spec to redline (8000 RPM) you get ~19 GPM.

Like I said before, as long as the relief valve is closed, all that flow is going through the engine. At operating temperature with 30wt or 40wt oil, the pressure is substantially below 85 PSI at 5,000 revs, so the flow through the system is indeed ~12 GPM.

It's hard for those of us raised on pushrod V8s to fathom, but I see no reason not to believe the specs and adjust our analysis for filters and oil appropriately.

 

[ZeeOSix]

Originally Posted By: gpshumway

My apologies if you think I'm being condescending, I'm basing my assessment on your third most recent post in this thread:

Originally Posted By: ZeeOSix
The unknown about these oil pump flow specs ... is that with no restriction of the engine on the pump's outlet, or is that the actual flow going through the engine's oiling system? If it's just the output of the oil pump without the restriction of the oiling system, then the actual flow through the engine could be less.


From this post it sounded to me like you thought placing a restriction on the outlet of the pump would have a substantial impact on flow. I also read your second most recent post a little too quickly and that mis-read reinforced my impression.


Let me clarify on what I meant. The flow rate through the engine certainly could be less than the pump could put out if the pump was in pressure relief. There wasn't much detail given about this Subaru oil pump spec when I made that comment, specifically if this was a pure pump performance parameter or if it was the actual flow performance of the engine's entire oiling system. The flow through the engine's oiling system certainly could be much less than the pump can put out if the pump's pressure relief valve comes into play when feeding the engine vs the pump just puking the flow output with zero resistance on the outlet.

Now that I see the snap-shot out of the service manual, it's obvious that these parameters describe the actual flow going through the engine's oiling circuit.

Here's a few comments about the specs shown in the FSM.

1) Oil is at 176 deg F. It will probably run around 200~210 deg F in normal use on the road unless this engine has some crazy oil cooler on it. That means when the oil is hotter and less viscous, the oil pressure numbers will be a little less at the engine RPMs shown in the FSM.

2) The oil pressure only changes 29 PSI over a 4,400 RPM range (600 to 5,000 RPM points). The oil volume changes 11.2 GPM over that same RPM range. This means this oiling system is very free flowing.

GM LSx family of engines typically change 10 PSI in oil pressure for every 1000 RPM increase in engine speed with 5W-30 Mobil 1 at 200~210 deg F - I have verified this on my LS6. This Subaru engine only changes 6.6 PSI for every 1000 RPM. With the oil at 200~210 deg F, the change will be even a little less.

3) The FSM shows that the PD pressure relief is set to 80 PSI. That means (based on comments made in 2 above) that the engine would have to rev (80 PSI - 43 PSI)/6.6 PSI per 1000 RPM = 5,600 more revs before the oil pressure hits 80 PSI. So, based on this it seems unlikely that the oil pump would ever hit pressure relief even with 176 deg F oil (and especially with hotter oil) unless the engine hits 10,600 RPM, and I doubt the red line is set there.

 

[ZeeOSix]

Originally Posted By: gpshumway
It's hard for those of us raised on pushrod V8s to fathom, but I see no reason not to believe the specs and adjust our analysis for filters and oil appropriately.


Not really ... LSx engines flow in the 10~12 GPM range too, but closer to red line RPM is needed, and the oil pressure is around 70 PSI as I showed in the graph I posted in this thread.

 

[ZeeOSix]

So in the Subaru FSM it shows two different filter specs ... are there two different filters part numbers specified by the factory for this engine? Physical size (OD and width) are shown differently too, so apparently there are two physically different filters specific in the FSM.

One has 73 sq-in of media and the other 124 sq-in. That's a big difference percentage wise. Both have the same 23 PSI bypass valve spec. Is the 73 sq-in less efficiency to allow the bypass spec to remain the same with the same oil flow going through it? Meaning, does the 73 sq-in filter flow better to achieve the same delta-P vs. flow as the 124 sq-in filter?

Mysterious ... since the filter's bypass setting is also based on the flow characteristics of the filter as well as the engine's oiling system. That's why the "23 PSI bypass" is a spec relative to the Subaru OEM filters that they are referring in the FSM.

 

[gpshumway]

Originally Posted By: ZeeOSix
Originally Posted By: gpshumway
It's hard for those of us raised on pushrod V8s to fathom, but I see no reason not to believe the specs and adjust our analysis for filters and oil appropriately.


Not really ... LSx engines flow in the 10~12 GPM range too, but closer to red line RPM is needed, and the oil pressure is around 70 PSI as I showed in the graph I posted in this thread.


Well, if we're scaling mentally we might assume that a 2.Xl 4 cyl would require half the oil flow of a 5.xl v8, just like you did in the other thread where you assumed a Prius wouldn't flow more than ~6 GPM. The reality is very different, as we've seen.

There are two filters mentioned in the owner's manual (I haven't thouroughly checked the FSM). The larger filter area I would guess refers to the Tokyo Roki filter with part number ending in "AA100", as that's approximately the filter area people have measured when dissecting those filters, and this FSM predates the Honeywell filters. The other filter mentioned in the owner's manual is P/N 15208AA09A, Subaru switched from the larger Purolator filter in ~2004 to the AA100, then to the AA09A, then back to the AA100 in ~2009, and now to the Honeywell filter as of ~2010. It's kind of like the Filtech "A01" vs. Honeywell "A02" filters with Honda, depending on who you buy it from and when, you might get either one.

The only other filter I can think of would be the Purolator made OEM filter which preceded the Tokyo Roki, but the outside diameter of those is substantially larger. Purolator still sells the old OEM filter for pre-2004 Subarus, 23 PSI bypass and all, it's P/N 14460. It's 3.15" in diameter and won't fit on a 2.5l turbo engine, it hits the exhaust manifold.

 

[ZeeOSix]

Originally Posted By: gpshumway
Originally Posted By: ZeeOSix
Originally Posted By: gpshumway
It's hard for those of us raised on pushrod V8s to fathom, but I see no reason not to believe the specs and adjust our analysis for filters and oil appropriately.


Not really ... LSx engines flow in the 10~12 GPM range too, but closer to red line RPM is needed, and the oil pressure is around 70 PSI as I showed in the graph I posted in this thread.


Well, if we're scaling mentally we might assume that a 2.Xl 4 cyl would require half the oil flow of a 5.xl v8, just like you did in the other thread where you assumed a Prius wouldn't flow more than ~6 GPM. The reality is very different, as we've seen.


Who knows what really goes in to the design parameters of an oiling system for every engine on the planet. It's apparently not always "scalable", but that's not to say that the the Subaru engineers might have went overkill on the flow rate. Many, many factors involved. I think engines that are turbo charged and have oil coolers probably have a higher than normal oil flow volume due to the fact that the engineers use the oil flow as a cooling medium.

I've got a 1300 cc 4-banger Hayabusa that puts out 180 HP and red lines at 11K RPM. You would think the oiling system would be flowing like mad, but the filter is tiny and doubt it is capable of supporting more than 5~6 GPM.

 

[Jim Allen]

I recite my diesel examples. 12 and 13 gpm for 6 and 6.4L diesels with HUEI.. an injection system that uses engine oil to pressurize eight injectors via a high pressure pump. They have HUGE turbos, oil coolers and very large oil filters and oil galleries. How they can need very little more flow than a 2.5L four is a mystery to me?

 

[ZeeOSix]

Originally Posted By: Jim Allen

I recite my diesel examples. 12 and 13 gpm for 6 and 6.4L diesels with HUEI ....
How they can need very little more flow than a 2.5L four is a mystery to me?


I think they have some over zealous oil system design engineers at Subaru.

As I said earlier, I think they are using a pretty high oil flow volume to help with cooling if there is an oil cooler on the engine. I had a twin-turboed RX-7 with twin oil coolers, as the rotary engine used the oil as much as the coolant to help keep the engine from burning up. Don't know what the oil flow was in that rotary, but I'm betting it was pretty substantial.