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Old 05-16-2011, 12:42 PM   #1
Concillian
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Default Low Oil presure causes

Normal oil pressure = ~25+ psi hot idle.

This oil change interval, hot idle pressure slowly dropped, 20 psi, 18 psi, 16 psi then one trip that included forgetting about the low OP and some high revs, it dropped to 8-10 psi hot idle.

Drove very gingerly home, changed the oil to be sure it wasn't something getting in the oil. Drove it around after oil change, still 8-10 psi hot idle. Other RPMs acting proportionally (low). Didn't rev it high enough to hit the bypass it was typically under 30 psi at 2700 RPM cruise in 5th.

I assumed it was oil pickup. I already had a pickup, ordered the 06+ pan conversion stuff when it was around 18-20 psi idle. Pulled the pan off yesterday and the pickup is fine, no crack. No bearing shavings in the pan. There were some bits of what seemed to be RTV stuck in the screen on the pickup tube, but it's likely those were from a little extra on the oil pan from the factory, it seemed to be the same kind of RTV... likely there since new. It was covering maybe 10% of the screen max, certainly not going to cause oil pressure issues.

Looking for other ideas of things to check out while I have things apart.


---------


I do have an oil leak somewhere in the rear area of the passenger side, I assume this is unrelated, a leak would have to be LARGE to put this kind of dent in oil pressure. Pictures of leak area (rear side of passenger side head area, it's not the turbo oil return, can see that and it's clean.)



There is some stuff on the vertical surface on the back of the head that's pretty coated, like the banjo for the coolant line to the turbo. But, as mentioned, the oil return on the turbo is not leaking.

Last edited by Concillian; 09-22-2012 at 04:00 PM.
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Old 05-16-2011, 01:15 PM   #2
Uncle Scotty
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what oil are you using??

sounds like the oil sheared way outa grade
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Old 05-16-2011, 03:36 PM   #3
Concillian
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It was Redline, and, as mentioned, brand new oil acted the same. The new oil was not Redline. Knowing it was potentially a really short interval I used the cheap stuff, normal 5w30 GTX I use in my wife's oil guzzling Corolla, but I'm pretty sure that didn't shear to the same point in 25 miles of freeway driving. Brand new 5w30 should be higher than 8-10 psi @ hot idle.

With the new oil, I think I have pretty much ruled out oil dilution and shearing.

Last edited by Concillian; 05-16-2011 at 04:37 PM.
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Old 05-16-2011, 11:53 PM   #4
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Quote:
Originally Posted by Concillian View Post
It was Redline, and, as mentioned, brand new oil acted the same. The new oil was not Redline. Knowing it was potentially a really short interval I used the cheap stuff, normal 5w30 GTX I use in my wife's oil guzzling Corolla, but I'm pretty sure that didn't shear to the same point in 25 miles of freeway driving. Brand new 5w30 should be higher than 8-10 psi @ hot idle.

With the new oil, I think I have pretty much ruled out oil dilution and shearing.
if the two oils mixed and the gtx didnt like the residual rediline in the engine...then yes, that could cause it

My suggestion would be to change the oil and filter again and see if that fixes the issue...that would eliminate that as possible
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Old 05-16-2011, 05:48 PM   #5
bluesubie
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With its high HTHS, Red Line 5W-30 would have op closer to a 40 grade. Looks like you've probably ruled out a pickup tube or oil issue. What about a gauge/sender issue?

-Dennis

Last edited by bluesubie; 05-16-2011 at 06:03 PM.
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Old 05-16-2011, 06:45 PM   #6
JamesWilson2
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Bad sender, or bad oil filter?
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Old 05-16-2011, 09:36 PM   #7
Concillian
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Sender is always a possibility, Prosport cheapie, but it seems to be acting right... Cold oil pressure shows bypass in the 75-80 psi range. Isn't that about right for the total range? Seems unlikely it would track pressure with RPM, be about right at cold oil temps, but then read extrordinarily low pressure at warm idle.

Filter was changed with the oil, doubt both were bad. If one let filter media go, then that should show up as restriction, right? That would be higher pressure.

I guess I'm just going to re-assemble tomorrow and hope for the best.
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Old 05-17-2011, 09:21 AM   #8
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Quote:
Originally Posted by Concillian View Post
Sender is always a possibility, Prosport cheapie, but it seems to be acting right... Cold oil pressure shows bypass in the 75-80 psi range.

That is LOW. 100psi or more for cold idle is normal.
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Old 05-16-2011, 10:31 PM   #9
Bacon117
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Worn main and connecting rod bearings can cause low oil pressure. It could also be idling lower than it should. This will most definitely cause lower oil pressure. There is a procedure for checking it at higher engine speeds in the factory manual. Find one and follow the specifications in there.
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Old 05-16-2011, 11:37 PM   #10
Rapier46
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There could be SOOOOO many things.... Attach a real oil pressure gauge to the oil sender and see what's up. Measure oil pressure how SUBARU specifies to. With the correct oil weight, temperature, Everything. If something is astray then, let us know.
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Old 11-21-2011, 01:52 PM   #11
screechy
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Did you sort this?

I'm having similar issues and have a slight leak around the pump. Hoping this is the only cause of my oil pressure but it's dropping right down when warm to the point I can't do more than 5 miles

Using a built cosworth 2.5 with modified oil pump, cosworth baffle plate.

For last 18 months: 8 bar when cold, warmed is 5-6 bar driving and 3 bar idle.

Then suddenly last week: 5.5 bar cold, dropping rapidly with warming to 1 bar driving. No change of pressure with engine revs.

Taken from plug under alternator with electrical gauge, verified by a mechanical gauge.

Car has only ever used Silkolene Pro S 10w50 oil.

Last edited by screechy; 11-21-2011 at 02:19 PM.
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Old 11-22-2011, 11:14 AM   #12
screechy
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Any suggestions welcome!!
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Old 09-22-2012, 04:07 PM   #13
Concillian
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Got a PM on this lately, here's the rest of the story:

- It was the sender, as verified by a Zeitronix sender hooked up to my ZT2. Oil pressure was actually fine.

- The Prosport sender was also the source of my oil leak. It was broken to the point of leaking. It wasn't leaking at the threads... it was leaking through a seam in the sender. The Zeitronix sender was also significantly easier to install, since the sender body was smaller than the 22mm hex, I could just fit a deep 22mm socket over it and wrench it in rather than dealing with crow foot attachments at odd angles.

- The leak got oil everywhere, including the passenger side CV boot... which softened it enough that it split... and I couldn't get the shaft out of the hub, so I replaced the entire corner of the driveline.

All told, that Prosport sender cost me nearly $1000 once I got all it's damage cleaned up. More if you count the oil pan conversion, but I have a Perrin header now, so that could be considered part of the header install since it doesn't fit with the 02 WRX pan.
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