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Discussion Starter · #1 · (Edited)
Hi all,

I have a 2017 wrx sti with 30,000kms, and a stock block. Among many other things it has:

csf radiator /oil cooler combo
Killer b pickup
Killer b pan
Killer b windage tray

I run 6qts 5w 30 redline oil currently but I have also run motul and regular Subaru oem oil. The car doesn’t burn any oil (that I can tell). And has an IAG aos.

I have an aem x-series oil pressure gauge which is hooked up to the oil galley behind the alternator via a pro sport relocation kit.

I have the following symptoms:

my cold idle is 75-80 psi. My hot idle is 23-26 psi. Cruising oil pressure varies from 40-65 psi. At wot as the revs climb the oil pressure starts to drop from ~ 55-60psi down to 49/50 psi flat at around 6k rpm. I know the fsm says it should be 56.8 psi min.

my thoughts are:

I was thinking that maybe I messed up the install of my killer bee pickup or something but then I wasn’t sure how I could get 80 psi cold startup. Then I was thinking maybe the csf cooler has a big pressure loss so I searched but couldn’t find any info on what ppl saw with it. I have ordered the male to male coupler so I can ditch the factory oil cooler and maybe gain some psi back there?

I’m a bit worried but the car runs fine.

Any help would be greatly appreciated.
Edit- I only recently noticed this because I only recently installed the oil pressure gauge.
 

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Discussion Starter · #3 ·
Unfortunately I don't have my pre-install pressure as I installed the gauge after I installed the oil cooler. I guess I will have to disconnect it, and run it and check and report back, I suppose I was hoping someone had a similar experience to mine.
 

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What do you think your pressure should be? And where is the sensor located?

there are a lot of factors that dictate oil pressure, oil temperature, oil viscosity, sensor location bearing clearances, and so on. It's hard to compare your setup to other unless you're comparing apples to apples.
 

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Discussion Starter · #6 ·
Sensor is located behind alternator via pro sport relocation stainless steel hose. Factory service manual for 2017 sti says @6k rpm pump pressure is 56.8 psi, I guess that should be the minimum value?
 

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Discussion Starter · #7 · (Edited)
They are 10 AN lines it was a mishimoto line kit, trying to find it on website to re confirm ya 10 an. They are definitely waaay too long for the location of the csf radiator and I will cut them down to a much shorter length and more direct route but (might be wrong here) I didn’t think I would get a huge psi drop from the lines as most oil coolers use pretty long lines anyways.

Killer bee stuff is great, I’m hoping that re routing the lines shorter and removing the stock oil cooler from the circuit will at least give me back the psi from the manual so that I can sleep at night.
 

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If they are crappy lines or fittings it can have an effect, but I wouldn't think that much. I would go to AutoZone and grab a mechanical gauge. They are cheap and pretty accurate; plenty accurate enough for troubleshooting.

The pressure is not 'bad' but it's not great. The dropping oil pressure at high RPMs also seems unusual.

Tanks for the kind words!
 

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The Pressure drop under WOT is due to the level in the sump dropping as oil is not being returned to the pan as quickly as the pump is supplying it.
That is surely possible, but has anyone ever heard of a non-worn out stock subaru that didn't maintain near max oil pressure at mid to high RPM?


What are the line sizes going to the oil cooler?

If they are crappy lines or fittings it can have an effect, but I wouldn't think that much. I would go to AutoZone and grab a mechanical gauge. They are cheap and pretty accurate; plenty accurate enough for troubleshooting.
. . .
The dropping oil pressure at high RPMs also seems unusual.
I think combine these two posters have identified your probelm, and I don't think you need to remove the stock oil cooler. The Mishimoto kit may or may not be the best, but I bet it's not normal even for it. That leaves something blocking flow in the instal, a sharp bend in a line, a place where it is squeezed, a kink , a truly defective part. Don't know what, but something.
 
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Discussion Starter · #10 ·
update so I did two things: I reduced the oil cooler line length by like 50-60% and I bought a mechanical gauge and set it up by zip tying it to the windshield wiper (lol).

took a quick drive, pressure not much different at all, at wot ~6k rpm it drops from 55-60 psi down to 48 psi at the lowest (as far as I saw).

so I guess that eliminates hose length/ obstruction or kinks, my gauge. I also didn’t see any metal in the oil when I drained it.

I guess I give up, it might be something in the pan/windage/pickup install that I fckd up but still wouldn’t explain how I get 80 psi at idle.

I am probably getting a shop to replace the short block this winter and I’m feeling lazy don’t wanna take the pan off right before winter. I guess when the motor gets pulled again the problem will reveal itself.

thanks for the advice thus far.
 

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update so I did two things: I reduced the oil cooler line length by like 50-60% and I bought a mechanical gauge and set it up by zip tying it to the windshield wiper (lol).

took a quick drive, pressure not much different at all, at wot ~6k rpm it drops from 55-60 psi down to 48 psi at the lowest (as far as I saw).

so I guess that eliminates hose length/ obstruction or kinks, my gauge. I also didn’t see any metal in the oil when I drained it.

I guess I give up, it might be something in the pan/windage/pickup install that I fckd up but still wouldn’t explain how I get 80 psi at idle.

I am probably getting a shop to replace the short block this winter and I’m feeling lazy don’t wanna take the pan off right before winter. I guess when the motor gets pulled again the problem will reveal itself.

thanks for the advice thus far.
The higher oil pressure at idle is due to the oil being colder and the clearances being tighter.
 

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I'm going to guess that you have a blockage or leakage from doing the KB parts install. Thus you only see a drop in pressure due to the increased centrifugal demand from more RPM's and yet the volume is restricted or some of the volume leaks back into the pan at higher flow rates. Flow rate is proportional to RPM's.
BTW, You could eliminate (bypass or disconnect) the external oil cooler and see if it acts differently.
My only worry is if you are really hard on the engine or there is a catastrophic failure of the problem area. Like the o-ring completely blows out for the pickup tube.
Did you make any changes to the oil pump bypass (shim, spring)?
 

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Pulling the pan and inspecting the oil filter are certainly things to do here, I would. It's pretty rare, but I have heard of instances where the o-ring was not on the pickup during install. I think that's what I would be hoping for here, as the alternative is not nearly as inexpensive.

You've checked the pressure with a second source and confirmed that it is not a gauge or sender issue. What was your normal oil pressure before doing the pickup install?
 

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Discussion Starter · #15 ·
Yea... crap I guess I will pull the pan, sucks doing with the motor in the car, when I installed all the KB parts I had already pulled the motor to do a clutch job. I hope I didnt hurt anything, I have done some pulls for sure, no track days with this issue tho.

I thought I was pretty meticulous when I did the install but who knows, it was my first time so... shit happens. Ill report back when I get the pan off.

Thanks again for all the input.
 

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Hey did you ever figure out what your issue is? I am having the same issue and took the CSF rad with built in oil cooler. Out of the equation and my oil pressure is back to normal. Either the CSF built in oil cooler is a crap design or defected from manufacturer. I’m thinking about contacting CSF and discussing this issue.
 

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Hey did you ever figure out what your issue is? I am having the same issue and took the CSF rad with built in oil cooler. Out of the equation and my oil pressure is back to normal. Either the CSF built in oil cooler is a crap design or defected from manufacturer. I’m thinking about contacting CSF and discussing this issue.
I guarantee its that CSF oil cooler. I have the exact same setup in terms of the KB Pan, Baffle, pickup and had the CSF Radiator/oil cooler. Was seeing 45PSI of oil pressure at WOT on track and talked to some track friends. They apparently had the same issue with pressure and told me to bypass/remove the oil cooler. Went home, removed it, instant 90+PSI the following day on track. I ended up buying a new one i'm going to be installing soon.
 

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Hey did you ever figure out what your issue is? I am having the same issue and took the CSF rad with built in oil cooler. Out of the equation and my oil pressure is back to normal. Either the CSF built in oil cooler is a crap design or defected from manufacturer. I’m thinking about contacting CSF and discussing this issue.
I should also note that before I removed the oil cooler, i sent off oil for analysis. This was their recent response:

"Metals are high for your EJ25, copper especially. Copper is from brass/bronze parts such as the turbo bearing and bushings. Silver is another bearing metal. You mentioned track use and that can cause more metal to show up, but there is likely excess wear with levels being this high, so watch for low oil pressure and listen for knocking."

I've got a 2020 STI with 12k miles on her. I'm sad to say i didn't have an oil pressure sensor installed when i first installed the CSF Radiator/oil cooler ... so i was slowly killing her without knowing it i think.
 
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