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Discussion Starter · #1 ·
So I have a new problem that has crept up, basically whenever I am under high vacuum (i.e. closed throttle, coasting at reasonable speed) I have what I believe is a burning oil smell. It goes away as soon as I open the throttle and isn't present under light vacuum (i.e. at idle). Also the smell is coming from under the hood, doesn't happen under boost and I have no noticeable smoke from the tail pipe, so I don't think it is the turbo.
I have done a little searching and seems like either it could either be valve stem seals or or the PCV system. It's a T5 so the PCV system is pretty simple, I have all new vacuum line, the Y-fitting and check valve are good.
Anyone have any ideas on anything else to check?
 

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under vac. the pcv check valve is open, you could be sucking oil out of the valve cover. how old is your oil,
 

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Discussion Starter · #3 ·
About 80 miles, OCI every 4K with T6, no difference with before or after oil change. Maybe to clarify it might not be burning oil smell but at least hot oil smell.

This is my understanding of the PCV system:
Under vacuum the TB sucks air out from the crankcase since air can be drawn through the check valve. Under boost to avoid the seals leaking when crankcase pressure increases air escapes from the crankcase via the Y fitting and rather than heading to the TB (since the valve is now closed 'cos no vacuum) it heads back to the intake pipe via the hard line.

Also I'm not consuming much oil, I think I was only about 0.25qt short at my last change, 4000 miles.
 

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pretty close. the check valve closes under boost to prevent the crank case from pressurizing which can cause a whole mess of issues. the line that Y's off into the turbo intake works as the new vac source to suck fumes out.
 

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no oil leaking onto your exhaust, or exhaust manifold is there?
 

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Discussion Starter · #6 ·
Ok gotcha. No oil leaks anywhere, plus I would think if it was something leaking on the exhaust it would happen all the time.
I'm gonna take a close look at the nipple on the valve cover, it has never been replaced (the gasket and vacuum lines have), maybe under high vacuum crankcase fumes being suck so much that they are seeping out there, though I would assume it would also happen under high boost too.
 

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verify that your check valve is working and installed correctly. blowing into one side should be free flowing, the other side shouldnt flow at all. the side that doesnt flow should be placed on the throttle body side
 
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