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Interesting oil usage experience - PCV

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1K views 1 reply 2 participants last post by  RocketRobin 
#1 ·
'04 Sti here, owned since new, mods in signature. 91,000 miles on it now. In past 10,000 miles I've done the timing belt, water pump and all the tensioner/idlers that go with that job, both valve cover gaskets (passenger side was leaking), and after that changed the oil filler tube 0 ring that was leaking.... which looked like a valve cover leak by the way, as the oil tracks down along the cover gasket under the car.

When my Sti was very new it consumed more oil than I expected. Needed to add a quart between 3,000 mile old changes sometimes. I also drove it pretty hard with a few auto crosses. Pretty quickly after say the first 10,000 miles, it consumed little oil. It seemed if I went on 3-5 hour high speed highway trips bumping it up to 80-90mph+ just for fun or passing, it would use some oil, maybe a half a quart. No worries really, just the way it was. If driven only 70mph on the highway, or just around town I rarely need to put oil in it. I check my oil every gas up. My valve cover and oil filler leaks were pretty small before replacing. Drops, not a lot, and I changed them out pretty quickly when discovered.

So when I just recently changed the oil filler 0 ring, for the heck of it I changed the PCV valve. It had not been replaced before. That little buggar is a PIA to replace! The old one rattled fine like it should. I put the new OEM Subaru replacement one in anyway.

Here is the funny thing. After a recent oil change that I now have about 2,500 miles on, with five pretty spirited 4-5 hour hwy trips, it has not used a drop of oil. That is definitely different than before.

I am wondering if a PCV valve with 90,000 miles on it that rattles just fine when removed, can actually cause some blow-by that a new PCV corrects? Seems odd to me, but that's what seems to be happening... not that I am complaining!
 
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#2 ·
After my engine broke in it started using oil too.

I asked my mechanic WTF? He said, "it's a boosted engine, there is a lot of pressure. There's nothing mechanically wrong. Monitor your oil level."
True enough.

I did my due diligence for my boosted engine: oil in your air intake will cause knock.

I've added a Grimmspeed AOS, which works with great alacrity!
 
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