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Old 12-23-2015, 11:29 PM   #1
xTourniquet
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Join Date: Apr 2008
Chapter/Region: MAIC
Location: Maryland
Vehicle:
2006 WRX Limited
Aspen White

Default Oil Pressure Drop / Fluctuation

I have a 2006 WRX with some oil issues I have been trying to diagnose unsuccessfully over the past couple of weeks. Any direction or help you guys can provide is greatly appreciated.

The Car

2006 WRX Limited
160,000 Miles (about 60,000 on the motor)

In early 2013 the motor was rebuilt due to a blown headgasket causing overheating. I figured while the motor was out I might have some upgrades done.

Here is what was installed at that time:

Manley Platinum Series Pistons
Manley H-Beam Connecting Rods
ACL Race Rod Bearings
ACL Race Main Bearings
ARP Head Studs
OEM Oil Pump
PCV Valve
Air Pump Delete
Killer B Oil Pickup Tube

I also have an AEM oil pressure gauge installed tapped into the block near the PCV assembly as well as the Grimmspeed AOS.

The Symptoms

I have been using Motul 5W-40 as recommended by the engine builder since the motor was completed.

Recently I have noticed the oil pressure drops by about 10-15 psi only when the manifold pressure is at or above 0 psi. For instance, at highway speed around 2,200 rpm oil pressure is bouncing around 72-75psi. If i accelerate the oil pressure holds until my boost gauge reaches 0psi, then oil pressure drops immediately to 60-63psi. If I back off the throttle, oil pressure comes back up to normal.

I also noticed that the oil pressure is only low until the engine reaches exactly 3000 rpms, then it comes back up to normal.

I do smell oil after accelerating. I pulled the intercooler and there is a good amount of oil in the intercooler and intake manifold. There is also oil in the turbo inlet pipe.

What I have Tried

I started with the obvious - checked the oil, level was fine. Changed the oil, made no difference. Replaced the PCV valve - no change. Rebuilt the turbo - also no change.

What I Plan to Try Next

Replace the current gauge - maybe this is an electrical issue.

What else could be causing these symptoms?
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Old 12-24-2015, 04:55 AM   #2
1qukSti07
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Location: Florida
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2007 STi
WRB

Default

The Grimmspeed AOS is garbage, you're getting blow-by if you have "a good amount" of oil in your intercooler. Get a quality one like IAG or Crawford.

Also, you have 60,000 miles on a built engine; it could be getting close to the end of its life depending how loose it was when it was built. Do you know what your P/W clearances were?

As for the oil pressure fluctuations, I'm a little stumped there... oil pump or sensor going bad?

I have my oil pressure sensor in the port under the alternator, which is directly above the oil pump where you'll get the most accurate readings.

Hope this helps a little. Good luck!
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Old 12-24-2015, 10:42 AM   #3
motorbykemike
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I have built quite a handful of v8's for street/strip w/a heavy strip bias

they were built very loose , bearing clearance wise

by gently varying the throttle/load you could make oil pressure go up and down

my bet is your issue is bearing clearances

and if that built motor of yours has 2618 alloy pistons it is probably nearing the end of it's "good" life
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Old 12-24-2015, 11:21 PM   #4
KillerBMotorsport
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Location: Virginia
Vehicle:
2005 WRX/STi
WRB of course

Default

Get a mechanical gauge (they are cheap !$15) to verify its not a faulty sensor or gauge. If pressure still reads the same, I'd guess it's just worn out. If the engine was built how most builders build these engines your clearances were on the large side from the get-go, and now they are REALLY large. As the loading on the crank changes so does the clearances since nothing is likely still round. Just my 2 cents.

Built engines wear out faster, period. Parts are heavier, you probably have an OEM sleeved block so the heavy parts have worn the bores to no longer be round as well. If you wanted to stretch it, you can cross your fingers and bump the viscosity.
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Old 12-28-2015, 10:42 AM   #5
spoolinsti05
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Try this stuff called motor silk it's supposed to be a permanent engine oil. I've been meaning to try it but everytime I have bearing issues I just beat the crap out of it until it spins lol
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Old 12-28-2015, 01:08 PM   #6
mopar3.0
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i had similar issue as that, happened out of no where on a new build, installed mechanical guage and got the car hot and it was fine again, drove the car and lost 2 rod bearings few days later.

i had to beat the bypass valve out out with a piece of coat hanger, So i figured the bypass was sticking open then the car was hot and closed when it cooled off, I was blaming the prosport gauge.......
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Old 12-28-2015, 04:30 PM   #7
rtv900
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The way you are describing those readings means at least one thing for certain, the gauge doesn't have the 'resolution' you want it to have.
Kind of like how a factory gauge either shows zero when off, or right in the middle under ALL other conditions.
A good pressure gauge practically responds like a tachometer, at least once the oil is hot, when it's cold it just high a lot of the time regardless.
Your gauge is jumping because it isn't accurate enough and it is only capable of showing you a reading every 10-15 psi with nothing in between.
I'm not saying there may not be another minor issue, but there's no point is messing around until you have a real analog gauge mechanically sensed that will show a needle sweep.
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Old 01-01-2016, 04:26 PM   #8
spoolinsti05
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Jr tuned TT Sleeved

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Is this car still running AVCS? If so can you disable it and then re check your data?
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Old 01-01-2016, 05:53 PM   #9
turbo sol
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San Remo

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I've always ran electric oil pressure gauges into the car cabin… do you guys run mechanical oil pressure gauges into the cabin?

I was under the impression this was a no-no > as you don't want hot, combustable fluids in the cockpit. (same with fuel pressure gauges)
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Old 03-01-2016, 01:49 PM   #10
xTourniquet
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Aspen White

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Quote:
Originally Posted by spoolinsti05 View Post
Is this car still running AVCS? If so can you disable it and then re check your data?
Yes - the car is still running AVCS. Your comment led me to AP datalog rpm, avcs, and boost to see what was going on. I do need some help interpreting the result.



Every time boost hits 0-1psi, AVCS also drops to 0. Is this normal? This is also exactly when the oil pressure is dropping.
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Old 03-02-2016, 12:00 AM   #11
wrx1392
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your oil pressure runs the AVCS so it may drop when it is activated
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Old 03-04-2016, 04:22 PM   #12
xTourniquet
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Quote:
Originally Posted by wrx1392 View Post
your oil pressure runs the AVCS so it may drop when it is activated
Understood - but I would expect a brief drop in pressure. Instead I am getting a 20psi drop the entire time I am accelerating.
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Old 03-04-2016, 05:39 PM   #13
subydude
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I was looking at my oil pressure gauge the other day and noticed something similar, but it was a smaller drop. Roughly 7-10 psi drop when I hit the gas. The oil pressure did seem to recover slowly, but I'll have to watch it a bit closer to see. I'm guessing your engine is still doing ok since it's been a few months since the original post.
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Old 07-25-2016, 04:01 PM   #14
xTourniquet
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Quote:
Originally Posted by subydude View Post
I was looking at my oil pressure gauge the other day and noticed something similar, but it was a smaller drop. Roughly 7-10 psi drop when I hit the gas. The oil pressure did seem to recover slowly, but I'll have to watch it a bit closer to see. I'm guessing your engine is still doing ok since it's been a few months since the original post.
No, last time I drove the car was about a month ago. The oil pressure dropped to about 35-40psi on the highway. Decided it was time to park it until I figure out what is going on.
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