educate me on oil pumps, please

[heartless]

the new to us 2004 Forester (EJ251) seems to be having oil pressure issues.. once it gets to full operating temp, the idiot light will flicker while driving, and come on full at idle (stopped at a light, etc) even tho it has plenty of oil.

never had an issue like this with the 02 which had the same engine.

I constantly see comments about upgrading to a 10mm pump, but have no idea which models had this pump, and the parts sites do not give that specific info.

[lmdew]

How many miles on the engine?  Most likely the bearing clearances are out of limits.  GD I'm sure can answer your Oil Pump question.  My understanding is it's the thickness of the gear in the oil pump.  The thicker it is the more volume the pump is moving.  I have a few pumps, but I've never identified them.

[idosubaru]

I think the 04 Forester got the tiniest dinky 7mm oil pump subaru ever put on an EJ engine.  Replace the pump with a 9mm version and tigthen backing plate screws.

I'd send one but I think I cleaned out all my EJ stuff.

If you want to try to keep the current oil pump, tighten the backing plate screws (a few/all of them are usually loose and that little pump doesn't need to loose any potential efficiency), install a new oil pump oring/crank seal, and reseal it to the block.

[88SubGL]

Could it be just a bad sending unit?

[1 Lucky Texan]

I've only ever had 1 car with an 'electrically' bad sending unit (some that leaked oil but reported OK)

It was on all the time.

The behavior of yours 'may' be indicative of truly low pressure. But, hey, even if it doesn't fix the issue, you get a new pressure switch on an 18 year old car.

[heartless]

8 hours ago, lmdew said:

How many miles on the engine?  Most likely the bearing clearances are out of limits.  GD I'm sure can answer your Oil Pump question.  My understanding is it's the thickness of the gear in the oil pump.  The thicker it is the more volume the pump is moving.  I have a few pumps, but I've never identified them.

187K on this car.... the 02 had over 280k and never had a problem like this.

We will be doing a full timing service on it very soon (as soon as the weather will allow) so, if looking at replacing the pump, i would like to have one on hand and ready to go.

I do have a 2005 parts car here, but it has the 253.. and around 165K, give or take.. so, in all honesty, would just as soon leave that one whole if I can for a possible transplant if needed

[heartless]

6 hours ago, idosubaru said:

Replace the pump with a 9mm version

and what years/models had this pump????

that is 98% of my problem.. no idea where to look

 

[Numbchux]

Yea, the pressure regulator in the oil pump can get weak and stick causing low pressure. Light flickering while drive it means you have single digits psi. NOT GOOD. That's alarming at an idle....Either that, or the clearances on your engine are getting so loose and the oil is blowing out faster than the pump can supply.

 

I think it was 2002 they switched from the 9mm to the 7mm rotor. I measured the one in my '00 Outback, and it was 9mm.

Basically everything in the '90s had the 9mm, but rumor has it the 2.2 ones were set at a lower pressure.

10mm is WRX

11mm is STi

 

Some JDM models have 12mm, and I think there's an aftermarket one that's 12, maybe a 13.

 

9 or 10mm is good. I got a deal on an 11mm one locally, and used that on my '00 Outback. In theory, this means the bypass will be open more, which can heat the oil and pull more out of the pan. But the way I drive and this climate, I'm not concerned about heat, and I check the oil level every time I fill up.

 

Quick google search turned up this page, which shows the OEM part numbers for 10, 11 and 12mm. https://www.outfrontmotorsports.com/subaru-oil-pumps

[heartless]

so.. any WRX is going to have the 10mm? or is it engine specific? 2.5 vs 2.0, or whatever?

and would a 2.2 version fit?

 

Edited February 14, 2022 by heartless

[lmdew]

From the Outback site:

When looking at the pump, at the 11 o'clock position, just below the top left bolt hole, there will be a number cast into the face of the pump. That is your pump "diameter".

While this is not Fuji gospel, the trend for oil pumps is as follows:

Non-AVLS, Phase 2 SOHC: 7mm
AVLS, Phase 2 SOHC: 9mm
Non-AVCS, Phase 2 DOHC: 9mm
Single AVCS, Phase 2 DOHC: 10mm
Dual AVCS, Phase 2 DOHC: 11mm

Typically, the more systems that require oil (AVLS, AVCS, Turbo), the "larger" the pump equipped.

If you're looking to "upgrade", I would not go larger than a 9mm on a non-AVLS engine. Too much oil IS a bad thing.

[heartless]

ok, so I dont want to go bigger than a 9mm.. gotcha

but again - what years/models??

I have no clue what has AVLS and what doesnt. doing a little bit of google it looks like AVLS did not become a "thing" until 2006?

 

[GeneralDisorder]

Any 2008+ STI will have the 11mm pump. We use them exclusively on all engine builds. 

That said - the horse has left the barn so-to-speak. 

All of the pumps are going to produce about 90 psi on cold start. An EJ engine with good clearances will be about 20 to 25 psi at hot idle. 

The idiot light comes on at a ridiculously low 4-6 psi. 

This is a common misconception - oil pumps produce FLOW and the size of the pump dictates VOLUME.

PRESSURE is a function of resistance to flow. What you have is a lack of pressure and thus a lack of resistance to flow. 

In every case I have ever seen this is due to significant wear in the main and rod bearings of the engine. The rod bearings we all know about. The mains get "loose" over time - especially the #2, #3, and #4 mains due to crankshaft deflection and compression of the cast aluminum block. 

Replacing the pump will not likely do much good for long. You can try. I would also switch to 20w50 on this engine to increase the idle oil pressure. I have seen borderline engines bump up 10-15 psi from thicker oil. 

Keep it cool and be gentle with it. It may last a few more seasons. 

GD

[el_freddo]

That little cast number at the 11 o’clock position is something I learned about last year and is great for identifying the oil pump size without removing the pump and measuring. 

I was going to ask what oil you’re running but GD kind of beat me to it with the thicker oil suggestion. 

Is the history of this engine known or is it a replacement engine or a new to you vehicle? 

Cheers 

Bennie

[heartless]

8 hours ago, GeneralDisorder said:

Any 2008+ STI will have the 11mm pump. We use them exclusively on all engine builds. 

That said - the horse has left the barn so-to-speak. 

All of the pumps are going to produce about 90 psi on cold start. An EJ engine with good clearances will be about 20 to 25 psi at hot idle. 

The idiot light comes on at a ridiculously low 4-6 psi. 

This is a common misconception - oil pumps produce FLOW and the size of the pump dictates VOLUME.

PRESSURE is a function of resistance to flow. What you have is a lack of pressure and thus a lack of resistance to flow. 

In every case I have ever seen this is due to significant wear in the main and rod bearings of the engine. The rod bearings we all know about. The mains get "loose" over time - especially the #2, #3, and #4 mains due to crankshaft deflection and compression of the cast aluminum block. 

Replacing the pump will not likely do much good for long. You can try. I would also switch to 20w50 on this engine to increase the idle oil pressure. I have seen borderline engines bump up 10-15 psi from thicker oil. 

Keep it cool and be gentle with it. It may last a few more seasons. 

GD

While i do greatly appreciate your expertise, I am kind of reluctant to accept bearing wear at this time... altho I am also aware that anything is possible.

the light thing is pretty recent and kind of sudden - as in just the last month or so (have had the car since Sept).. it also started just after an extreme cold snap...the light is out while driving at speed (over 2000rpm) but at lower speeds (rpms) is when it flickers, and on full at low idle.

I dont go out a lot, but do have to drive some distance when i do go out (30-ish miles one way) so it does definitely get fully warmed up on an outing.
there is no rattling, knocking, or other indication that there are any major problems - even on a cold start... doesn't even have the gnarly sounding piston slap that the 02 was plagued with, lol

I am more inclined to think that the backing screws on the pump may have loosened up.. (hoping?) It is also due for an oil change, so yeah, I can easily bump up the oil grade - currently has 5w30 in it (recommended grade). 20w50 is probably a bit much for this area this time of year, however.. we can still get pretty extreme cold temps right thru March  10w30 or 10w40 would probably be more appropriate, i feel..

history on the car is pretty much unknown, but going by general overall condition, mileage is pretty consistent with the general condition. i suppose it is possible that the engine had been swapped, but i really dont see anything that would lead me to believe that had happened.. there is a note written in marker on the front cross-member about the timing having been done at 137K in 2013 - and yes, I am aware we are at the limit time wise which is why it is high on the list.

[el_freddo]

13 hours ago, heartless said:

there is a note written in marker on the front cross-member about the timing having been done at 137K in 2013 - and yes, I am aware we are at the limit time wise which is why it is high on the list.

I’m always cautious on this - the note could be the last time the belt and kit was changed, it could also be the second or third last time too... you just never know when it comes to vehicles that are new to you unless the PO told you truthfully about the last service of these items. 

Just saying. 

Cheers 

Bennie

[idosubaru]

22 hours ago, heartless said:

there is a note written in marker on the front cross-member about the timing having been done at 137K in 2013 - and yes, I am aware we are at the limit time wise which is why it is high on the list.

As important as the belt age - it may not be a Subaru belt, and the lower toothed idler failing. The lower idlers are ubiquitously in poor shape by the age of that car and belt  

checking oil pressure with a gauge before and after addressing the pump would potentially confirm it was the issue.

Good luck! Hope you can knock this out soon!

[heartless]

appreciate the warnings guys, and yeah, normally I do address the timing right away, but this time there was some major difficulties locating & obtaining the Aisin water pump and one of the pulleys for this car and if i remember right it was the toothed one..Aisin kits were also unavailable... assuming due to the supply line issues that are ongoing.. by the time we finally got our hands the correct parts, we were full into winter and currently no access to garage space...

again.. everything appears consistent with this car.. nothing suggests anything major has happened in its past - and that includes getting the title sorted out.. dont remember if i posted about that here or not.. but when we went to transfer title online, it popped up that there was a lien on the car in WI records.. I made multiple phone calls, including to the state of Illinois where it came from and according to them, there were never any liens as far as they were concerned. The lady also told me that the car had only ever been titled twice in its life (before us) - once in Kansas when new, and once in Illinois when it moved there.

Don't know where the lien came from, but since there was no record of it on the old title it did get sorted out.. It is possible that a number got transposed somewhere, I dont know.. all i know is we do have the clean, clear title now, and that is about all i care about on that front.

[nvu]

7 hours ago, idosubaru said:

checking oil pressure with a gauge before and after addressing the pump would potentially confirm it was the issue.

probably a good idea to install an oil gauge at this point.  it's a non turbo so you probably have plenty of room to tap into the rear oil gallery plug.  search for oil pressure sender gauges.  i prefer the metal can looking ones with no plastic connectors that melt when placed near a turbo.  don't ask how i know.

it doesnt have to be routed inside.  the gauge could live in the engine bay for diagnostic, taped to the hood, or unplugged if not needed.

[GeneralDisorder]

I would recommend two things:

1. Check the oil pressure at the port used by the idiot light with a mechanical gauge. Make sure you have the engine fully up to temp. The oil pressure will keep dropping for likely around 20 minutes as the engine oil reaches full temp and stabilizes. 

2. Assuming this comes back with a hot idle pressure reading of under 10 psi...... cut the oil filter and inspect. 

I have not seen any significant failure rate with the idiot light switches - I've seen a couple leak but that's it. They are a rock solid part and I have especially not seen one react exactly the way you would expect it to react under a low oil pressure condition without that condition actually being reality. 

Further I have never seen a situation on any engine where replacing the oil pump fixed the low oil pressure condition. And applying science and logic to how pumps work makes it pretty obvious why that is the case. The pump isn't the source of the "pressure" that the switch is reading. Bearing clearance is the source of the pressure - or rather the lack of excessive bearing clearance. 

I've been doing this a LONG time. Back when my EA81 in my off-road lifted wagon had the flickering oil idiot light at idle..... I was about 20 years old (man - has it been 22 years? crap) and didn't recognize the symptoms. I resealed the oil pump and that indeed brough the pressure up just enough to kill the light. About 2,000 miles later it threw a rod on the freeway.

IMHO - you have about a 1% chance it's something to do with the idiot light switch, and about a 99% chance that engine is going away internally. 

GD

[Numbchux]

^Excellent post right there!

 

I've heard of the regulator/bypass spring in the oil pump getting weak and allowing oil pressure to bleed off, which seems plausible but I've never seen it. And absolutely might be an anecdote, where someone replaced an oil pump and it seemed to get better, but it may not have made it to it's next oil change.

[GeneralDisorder]

4 hours ago, Numbchux said:

^Excellent post right there!

 

I've heard of the regulator/bypass spring in the oil pump getting weak and allowing oil pressure to bleed off, which seems plausible but I've never seen it. And absolutely might be an anecdote, where someone replaced an oil pump and it seemed to get better, but it may not have made it to it's next oil change.

 

I've never seen that on a Subaru. And the backing plate screws being loose was exclusively a 90's thing from what I recall. Haven't seen that in a lot of years. 

I've encountered a couple "back yard rebuilds" where the oil pressure light flickered at idle with 30 weight. Main bearing clearances would be my guess. The last one I tested with my Pico scope and pressure transducer was running about 4-6 psi. We put in 20w50 and that came up to about 14 psi and the customer wanted to send it so we dyno tuned it and AFAIK it's still running but I'm not 100% - I haven't seen it for about a year. 

GD

[heartless]

ok, to close this one out...

finally got around to changing the pressure sending unit (one wire sender, threaded into the block under the alternator) - got a new unit installed, wiped down the plug (old sending unit was leaking a bit of oil) plugged it back in, and no more flickering oil light.. it was a bad sending unit after all..

 

[88SubGL]

Hey, I was right for once. Glad you found the problem.

[heartless]

20 hours ago, 88SubGL said:

Hey, I was right for once. Glad you found the problem.

yup, you got it right...

and i drove around for several months with the silly thing unplugged, too.. made an attempt to get at it back in March or so.. but could not get the alternator tensioning bolt (the long one) to budge at the time... soaked it in penetrating oil, and then kinda just let it go/forgot about it.. until we got around to doing the timing job.. that bolt did break.. thank goodness for parts cars!

[jonathan909]

Sending unit failures may be very rare, but they're so quick+painless to change that it's crazy not to try it first.  The only oil pressure related problem I've ever had was four or five years ago - my wife was en route home from work (an hour drive) in the '98 EJ22 OBW when the idiot light came on.  I told her to stop right where she was and have it towed home.  Unscrewed the sender, screwed in a gauge, verified pressure, stuffed in a used junkbox replacement, and it's still on the road.  Why get caught up in complicated speculation rather than trying the easiest fix first?