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Old 12-05-2019, 11:27 AM   #1
rockiesskier
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Member#: 509052
Join Date: Dec 2019
Default Low oil pressure at idle once warmed up

Hello there fellow Subie owners,

I've been viewing these forums to help fix up Subaru's for years and first would like to say a huge thank you to all the contributers!! Go easy on me as this is my first post!

The car = 2007 Impreza manual wagon with 2.5L engine, all stock.
The issue = Flickering low oil pressure light keeps coming on at idle when the car is warmed up, after about 15 minutes of driving usually. Took a turn for the worse yesterday and car started completely dying on me at idle.

I've changed the oil pressure sensor and don't think that's anything to do with the issue. I took it to a local garage a while back and they checked the pressures and told me it was actually reading much higher pressure than spec (can post results later) over a range of RPM.

I've buried my head in the sand and ran with it like that for months (terrible idea I know, and I realise I've risked totalling the motor) but yesterday the car totally cut out on me in town. Light was flickering much more than it usually does, almost permanently on at low idle. Stalled 4 times in 10 minutes but I limped it home, the car would start immediately after stalling out and run again and as long as I keep the revs up then it won't stall. Car feels like it's struggling to stay running at idle, kind of like it's not getting enough air or fuel.

I plan to cut open the oil filter and look for metal as soon as I can. Any other tips on what might be causing the issue? Should I just take it to a shop and ask them to change the oil pump and oil pick up? From what I've read it seems like a cracked pick up is a fairly common cause of oil pressure issues. But the shop I took it to said they didn't think it was the oil pick up, because of the high pressure readings they got with the manual gauge.

Appreciate any advice the resident experts can give, think I've reached the limits of my car problem diagnosis skills!! Thanks in advance.
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Old 12-12-2019, 11:19 AM   #2
rockiesskier
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No-one got any thoughts?

I cut the oil filter open yesterday and didn't see anything too concerning in there. Some tiny specks of metal but with a 230,000 km engine I don't think that's unusual, my mechanic friend didn't think it was much to worry about.

Since that night the car hasn't cut out on me again, oil pressure light still flickering when engine's warm but no stalls since.

Thinking I'll take it to a shop and ask them to inspect/replace the oil pump and oil pick up. Would still love any ideas people out there have on my situation, thanks.
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Old 12-12-2019, 11:21 AM   #3
firebane
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Have you hooked up a mechanical oil gauge to see if its an issue with the sender or switch?
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Old 12-12-2019, 11:34 AM   #4
Waddlz
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2012 STi
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Go to your local part store and rent a mechanical oil pressure gauge, then report back what your oil pressure is.
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Old 12-12-2019, 12:49 PM   #5
rockiesskier
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Just to confuse things, when I took it to the local shop with the problem they put a mechanical gauge on it and told me it actually reads HIGH, not low pressure.

@ 600 RPM ACTUAL = 90 PSI
@ 3000 RPM ACTUAL = 60 PSI

Maybe I should rent a gauge and test for myself. Would a rental thread directly into the port where the sensor is? I replaced the sensor myself when I bought the car cos it was leaking, so I believe it to be good. Thanks
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Old 12-12-2019, 12:54 PM   #6
firebane
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Quote:
Originally Posted by rockiesskier View Post
Just to confuse things, when I took it to the local shop with the problem they put a mechanical gauge on it and told me it actually reads HIGH, not low pressure.

@ 600 RPM ACTUAL = 90 PSI
@ 3000 RPM ACTUAL = 60 PSI

Maybe I should rent a gauge and test for myself. Would a rental thread directly into the port where the sensor is? I replaced the sensor myself when I bought the car cos it was leaking, so I believe it to be good. Thanks
Most gauges is 1/4 NPT so not sure what your setup is but they usually come with adapters and such.

Were those readings when the car was cold? Because mine will read over 100psi when cold and settle to about 40psi at idle.

Even still those numbers indicate healthy oil pressure and leads me to think your dummy light switch is bad.
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Old 12-12-2019, 01:04 PM   #7
rockiesskier
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Thanks Firebane. I specificially told the garage that the problem only occurred when the engine was hot, so I presume that they took pressure readings after warming it up properly, but I didn't verify with them at the time.

So you think it might just be the wiring to the light on the dash? I've wondered that too, but can't explain why it would only flicker when the car is fully warmed up? No issues with any of the other lights on the dash either.
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Old 12-12-2019, 01:06 PM   #8
firebane
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Quote:
Originally Posted by rockiesskier View Post
Thanks Firebane. I specificially told the garage that the problem only occurred when the engine was hot, so I presume that they took pressure readings after warming it up properly, but I didn't verify with them at the time.

So you think it might just be the wiring to the light on the dash? I've wondered that too, but can't explain why it would only flicker when the car is fully warmed up? No issues with any of the other lights on the dash either.
I would say for the cost of the switch and how simple it is to swap out just swap it and see if the issue goes away.

Like I said those readings are fine.

Its a reason why so many people say spend the money and throw a proper oil pressure gauge into the car for. It may not seem like a big deal but when your driving around I'd rather know what my oil pressure is then have a light come on and confuse me.
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Old 12-12-2019, 01:20 PM   #9
rockiesskier
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Makes sense, I will switch out the sensor again. For a $10 part that takes 1 minute to fit, I'll try it before I go for any deeper fixes/inspection.

Never considered fitting a proper full time oil pressure gauge on the car but guess I could. How hard is that for a very amateur home mechanic?!

Just noticed your advice is coming from Calgary, I'm based in Canmore as it happens! Thanks very much, I'll post once I've tried a couple more things
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