John 37

My 08 STI uses quite a lot of oil. Not checked exactly but around 1000 miles per litre. Last MOT emissions were high and the exhaust tailpipes are black with soot. I recently replaced the head gaskets and all bores were fine. Heads were left alone. The car is basically standard with Milltek 3" exhaust and K&N panel filter. It's been mapped by Duncan of Racedynamix and gives 340bhp. When the engine was out, I cleaned the IC. I've checked it today and there's a light oil covering inside it. Don't know how much is acceptable.
I've been told the 2.5 engine uses oil but this seems a lot. Is it?
Could my oil consumption cause high emissions and black exhaust?
Sorry for so many questions.

Don Clark

Black exhaust tips are pretty standard for turbocharged Subarus as they run rich and hence the demise of the WRX STI in Europe due to low emmisions requirement.
Some oil is also expected in the intercooler due to how the OEM pcv system works.

Cleaning or changing your pcv valve may improve matters.

Personally have being running an AOS for the last 7+ years and oil consumption improved as did the cleanliness of the intercooler.
For all that time the car has been running the Pro-R 340 map with BOTH OEM cats in place but H&S mid pipe and backboxes plus K&N filter.

Tomioka Racing AOS no longer available.

John 37

Thanks. That's a tidy looking engine.
I've looked at AOS devices. The Grimspeed one looks similar to yours and should be easy to fit.
A few of questions.
I can see where 2 pipes go to. Does it go to the PCV?
Where is the PCV?
There's a small solenoid valve located just behind the breather T piece in your photo. What does it do? Mine's got a broken pipe. When I enquired, Subaru UK had non so I repaired it with araldite. Unfortunately it didn't hold. I will try again but I'm not too confident it will be any better.
Thanks again for your help. As you can tell, I'm still learning this car.

Gambit

iTrader: (6)

I assume when headgasket was done that a compression test & leakdown test was performed and everything was ok?

My old hawk which was on std internals used a lot of oil which an AOS did help a bit but I was more like 3000 mile to a ltr.

1000 mile to a litre would make me think you've maybe a cracked ringland, or you are using 5w oil which imo is too thin for 2.5's

Don Clark

The pcv valve is located in the inlet manifold below the throttle body.(5)


There is a breather vent (11) on the crankcase which goes to a Y piece (5). One leg of the Y (6)connects to the pcv valve the other (3) goes to the turbo inlet pipe.(In the US this has a monitoring sensor installed as well)



The pipe "Tee'd"shown in my pics, goes to the leg that used to go to the turbo inlet pipe keeping the pcv valve in use for off boost operations. The connection to the turbo inlet pipe is blanked off/capped


The solenoid valve located below the Tee piece - this one (item 13 of first picture)?



Purge Control solenoid - Part of the emission control system.



The Grimspeed is very similar but has two inlets so the Tee is not required and can be piped direct to the unit.

John 37

Thanks for everyone's help.
I've just removed the spark plugs (left rear was a real ####) and done a compression check. Front cylinders were both 120psi, rear were both 135psi. That's more variation than I would like but is it significant?
Plugs were all the same as here

BTW, I use Fuchs Race Pro S 10W50.
I'm trying to convince myself it's not the pistons. I don't really want to take the engine out again.

1509joe

iTrader: (2)

Long are those plugs in they're too clean don't like the look of them.

Don Clark

From the Manual

Perform at least two measurements per cylinder, and make sure that the values are correct.
Compression (throttle full open):

Standard
981 — 1,177 kPa (10 — 12 kgf/cm2, 142 — 171 psi)


Difference between cylinders
49 kPa (0.5 kgf/cm2, 7 psi), or less