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Pressure under oil cap?

GTI.

E
Location
Jerz
Car(s)
07 GTI
To make a long story short...

a week ago, I noticed a ton of specs of oil all over my engine bay. Mainly on my intake and top of valve cover. So I took it into the dealership and they replaced my valve gasket. So a member of GOLFMKV mentioned to me that valve gaskets do not fail randomly and the problem must be something else. So I checked to see if there was pressure under the oil cap and noticed that there is. With the oil cap off, I noticed air was being pushed out.

Judging by where the oil was on that day I noticed the leak, it seems as it could of easily came out of the oil cap.

Do you guys think this is a bad pcv valve system? Should I put it a PCV fix by BSH or another company? Please anything to help. Now I'm worried :frown:
 

GTI.

E
Location
Jerz
Car(s)
07 GTI
btw can someone tell my how to check to see if my front PCV valve is bad? I remember reading up that there was a way to do it but can't seem to find anything,


thanks in advance!
 

Timvgti

Ready to race!
Location
Netherlands
Subscribed (cause I'm also interested in how to check bad pcv)
When I remove my oilcap while engine is running I also notice pressure. Don't know if it is suction or blowing. Have to check.
But isn't this normal?
 

Chris@RT

Banned
Location
ga
If you are blowing oil out then yes there is a chance the check valve is faulty in your PCV and needs to be replaced.

Also valve cover gaskets do just fail, they are rubber and have a limited life.
 

Timvgti

Ready to race!
Location
Netherlands
No oil is blowing out. But I hear/feel/notice pressure when I remove the cap while engine is running. This isn't normal on a 2.0fsi turbo axx?
 

Chris@RT

Banned
Location
ga
No oil is blowing out. But I hear/feel/notice pressure when I remove the cap while engine is running. This isn't normal on a 2.0fsi turbo axx?

That is normal on just about every car produced.

If the vacuum is so strong you have to try harder to pull the cap off then when the car is running then you probably have a bad PVC. If the car dies when you pull the cap off then you also have a bad PCV.
 

GTI.

E
Location
Jerz
Car(s)
07 GTI
That is normal on just about every car produced.

If the vacuum is so strong you have to try harder to pull the cap off then when the car is running then you probably have a bad PVC. If the car dies when you pull the cap off then you also have a bad PCV.

interesting. everyone tells me that air coming out (pressure) means that the pcv is bad. You're saying vacuum is what signals a bad pcv valve? I think I'm just going to change it out for peace of mind.
 

Chris@RT

Banned
Location
ga
interesting. everyone tells me that air coming out (pressure) means that the pcv is bad. You're saying vacuum is what signals a bad pcv valve? I think I'm just going to change it out for peace of mind.

PCV stands for Positive crankcase venitilation. There is pressure in the crankcase if you open the cap you now have created the path of least resistance and you will get pressure coming out of the 1.5" hole vs the .5" hole that is the PCV.

With a PCV system like ours routed back to the intake the point is that whether the vacuum the turbo creates at part and wot or the vacuum is created by the intake manifold at idle it will see vacuum however not too much vacuum. Having too much vacuum will actually literally suck oil right out of the crankcase which is actually more common then the other way with boost blowing into the crankcase.

If you look at that round flat part of the front PCV portion that is a restrictor, at WOT the path to it is closed by a check valve near the connection for the hose going to the intake manifold this prevents boost from blowing into the crankcase defeating the purpose of the PCV.

The opposite though when the car is at idle or under vacuum in the intake manifold at part throttle the rubber diaphram in the restrictor pulls itself more and more closed. The higher the vacuum the less flow. So if you have the car running and attempt to open the cap but cannot due to the strenght of the vacuum or the car stalls out because having the cap open is drawing in that much unmetered air then you know that restrictor failed, quite common for the rubber to tear.

Now if you have so much pressure that the cap blows off or is blowing oil out then you probably have the failed part of the valve that is supposed to seal shut with boost. Oddly this seal works better with more boost (like a DV) and isn't usually increased boost that kills it. STock your car can make 20+psi but is requesting 12 so if it has a leak of say 2psi it can make 14-15 to make the boost it wants, people just don't notice that it fails until their software that is supposed to make 20psi only makes 15 because the leak is greater then what the car can compensate for.
 

Timvgti

Ready to race!
Location
Netherlands
Chris@RT: Thanks for the good explanation.
So just a little suction/vacuum when removing the oilcap is 'normal'? Looking at my youtube videos above???
 

707Stang

I'm Hella From Nor*Cal
Location
Nor*Cal
yeah a lil vacuum on the oil cap is fine pull your dipstick with the car running and the same thing will happen. all normal. positive pressure pushing on the cap is a bad thing, time for a new pcv
 

GTI.

E
Location
Jerz
Car(s)
07 GTI
fair enough. just ordered a new one. I'm pretty sure that oil spewed out of my oil cap that one time.

Do you guys know if I have to change the PCV valve gasket when replacing a PCV valve or can I use my old one? Thanks again
 

ronmexico

Ready to race!
Location
Brooklyn
PCV stands for Positive crankcase venitilation. There is pressure in the crankcase if you open the cap you now have created the path of least resistance and you will get pressure coming out of the 1.5" hole vs the .5" hole that is the PCV.

With a PCV system like ours routed back to the intake the point is that whether the vacuum the turbo creates at part and wot or the vacuum is created by the intake manifold at idle it will see vacuum however not too much vacuum. Having too much vacuum will actually literally suck oil right out of the crankcase which is actually more common then the other way with boost blowing into the crankcase.

If you look at that round flat part of the front PCV portion that is a restrictor, at WOT the path to it is closed by a check valve near the connection for the hose going to the intake manifold this prevents boost from blowing into the crankcase defeating the purpose of the PCV.

The opposite though when the car is at idle or under vacuum in the intake manifold at part throttle the rubber diaphram in the restrictor pulls itself more and more closed. The higher the vacuum the less flow. So if you have the car running and attempt to open the cap but cannot due to the strenght of the vacuum or the car stalls out because having the cap open is drawing in that much unmetered air then you know that restrictor failed, quite common for the rubber to tear.

Now if you have so much pressure that the cap blows off or is blowing oil out then you probably have the failed part of the valve that is supposed to seal shut with boost. Oddly this seal works better with more boost (like a DV) and isn't usually increased boost that kills it. STock your car can make 20+psi but is requesting 12 so if it has a leak of say 2psi it can make 14-15 to make the boost it wants, people just don't notice that it fails until their software that is supposed to make 20psi only makes 15 because the leak is greater then what the car can compensate for.

Excellent explanation, I think I learned a few things. Thanks!
 
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