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Old 04-02-2008, 05:35 PM   #1
surowrxa
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Member#: 102895
Join Date: Dec 2005
Chapter/Region: MAIC
Location: Pittsburgh
Vehicle:
'12 Forester
'08 Legacy

Default Blowby:causes, effects

Stock 2005 WRX has just been diagnosed by the dealer as having bad seal(s) in the turbo, allowing oil to get into the y-pipe.

My question is, aren't there more reasons than just bad turbo seals for oil to get past the turbo? Bad rings can load up the turbo with oil, and the seals are made to release some is my understanding of one other scenario.

I am trying to avoid the same thing happening again. Thanks for opinions. No smoke coming from the exhaust, and they quick checked the uppipe (by hitting it) to make sure the cat is still one piece.

Thought about putting this in Factory 2.0 Powertrain, but this can be an issue for 2.5's as well...

edit: they also did not think oil dripping from the y-pipe meant a bad y-pipe, that it was oil coming from the turbo causing this. Isn't the y-pipe sealed? I'm guessing this is why I don't see smoke because a large amount of oil really isn't making it all the way through the intercooler.
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Last edited by surowrxa; 04-02-2008 at 06:48 PM. Reason: clarification
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Old 04-02-2008, 10:43 PM   #2
bulwnkl
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Join Date: Aug 2003
Location: Arizona
Vehicle:
2005 Black Tiger
(Black Turbo Baja)

Default

Oil could be coming past the turbo from the combustion chamber, but it's far more likely to be a turbo-source issue. If it was coming from upstream of the turbo, it may be a valve seal issue. When the valve seals leak, the engine will actually suck oil in when you close the throttle (deceleration). This is often accompanied by a blue puff when you first close the throttle. BMWs are absolutely famous for this. Ring blow-by can cause oil consumption, too, but that's mostly burned up during combustion unless it's really bad. If this was the source you'd see oil on the compressor and in the pipe upstream of the compressor.

To answer your post title question: Blow-by is 'caused' by the rings not sealing against the cylinder walls. This can happen due to excessive wear, but also very commonly happens when the rings (especially the oil control ring) carbon up. The former is fixed by honing or boring and replacing the pistons and rings with oversize parts. The latter can be fixed without that kind of mechanical intervention, but if tackled the wrong way the efforts don't do any good.

Effects are: Reduced power output, oil consumption, coked/oxidized oil, reduced mpg...
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Old 04-02-2008, 11:05 PM   #3
surowrxa
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Member#: 102895
Join Date: Dec 2005
Chapter/Region: MAIC
Location: Pittsburgh
Vehicle:
'12 Forester
'08 Legacy

Default

Thanks Bullwinkle.

The weird part is there are no oil consumption issues related to this. Power loss is possible (seems sluggish), but with snow tires on I have not seen above 4-5K rpms in months, hard to discern. MPG is crappy, but every winter it gets crappy. Oil was sent away today to Blackstone from the last oil change. Hopefully it shows some clue of what's really going on.

Turbo is set for replacement next week under warranty.
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