Understanding the MK7 PCV function, retrofitting the MK8 PCV, and why catch cans are bullshit(IMO)

[DerHase]

Where can I find this data?

Loosen your oil cap at idle.

I sent my adapter to a guy in Florida who drove around with the APR CC on his GTI. At idle it pulses slightly positive pressure. We're talking 0.1-0.2psi. obviously not a "huge" amount, but there's very good reason literally zero engines are run like this from the factory.

Been a busy last ~month but will share the video when I get a chance.

There are MANY people who have reported noticeable oil leaks starting shortly after CC/plate installs.

The reason catch cans work on other platforms is they are not completely getting rid of the vacuum circuit. Our cars are kind of unique in the way the PCV is implemented.

As alluded earlier, it REALLY needs to go between the port in the cyl head and the corresponding path in the PCV valve.


All that said, my holes-drilled MK8 PCV was put on and drove the car around last night with no ill effects. Normal ~1.5inHg vacuum at idle. Pulling from the cam cover in addition to the oil port might be a way to keep oil in the bottom end.

My non modified valve does have a tiny bit of oil residue in the intake port. I have no doubt they all ingest a tiny bit of oil stock, as long as it's not enough to matter it's fine though. This is after sitting the valve on its side for 20 min while I installed the modified one. Had an oil film but no apparent accumulation on initial removal FWIW.

 

[Mosquito]

I just looked up the F version and it doesn't have the sensor port? MK8 PVC 06Q103495F. Would this not be the way to go? so we don't have to worry about the sensor blank?

495F shows up on models which until now run smaller turbo and lower boost threshold. None of those models are "performance" models. The PCV is different though.

 

[ITGUY]

06Q103495F

06Q103495B

Yes I see the difference in the designs. Shrug was worth a look.

 

[scrllock]

I just looked up the F version and it doesn't have the sensor port? MK8 PVC 06Q103495F. Would this not be the way to go? so we don't have to worry about the sensor blank?

It does have the sensor port. Like Mosquito said though, it's from models that are presumably engineered for less boost pressure.

You might have other issues going on and it might be difficult to trace and find out.
In your shoes, I would want to get some leakdown information from rings. Getting some idle crankcase vacuum numbers to compare with what is known and asses if there might be a leak keeping the PCV vacuum from essentially sealing the system, Then a run across the rpm range to gauge when you aproxímate ambient pressure or move past it. What pushes oil up is a crankcase that operates close to or above ambient pressure, it also makes blowby oil less dense. Your starting vacuum would also make you run vacuum over a smaller window within the RPM range, specially at the switch over between vacuum sources. The ability of the PCV to do its job is entirely dependent on properly managing the pressure differentials across it. We only see smoke as the symptom, but it isn't the sickness if you will.

Been suggesting this to him, I really suspect he has other issues that a compression or leakdown test will illuminate.

 

[Mosquito]

06Q103495F
View attachment 294533
06Q103495B
View attachment 294535

Yes I see the difference in the designs. Shrug was worth a look.

It is worth a test. I just went with the "safer" one if you will. That said, if new performance builds start showing up with 495F, that might mean something...

 

[JerseyDrew77]

I sent my adapter to a guy in Florida who drove around with the APR CC on his GTI. At idle it pulses slightly positive pressure. We're talking 0.1-0.2psi. obviously not a "huge" amount, but there's very good reason literally zero engines are run like this from the factory.

Ok, so how does the APR plate create this slightly positvie pressure at idle and did it create more under acceleration?

 

[mrmatto]

@DerHase you need this shirt

 

[Mosquito]

Ok, so how does the APR plate create this slightly positvie pressure at idle and did it create more under acceleration?

Cylinder pressure, blowby, volume displacement within the crankcase by the down stroke. After the volume is filled with pressure, it gets pushed out through the balance shaft, up the crankcase vent and in reverse through the oil drain ports on the cam cradle, eventually through the APR baffle plate, to the CC, through all 6 baffles and to a TIP that is nearly stagnant in airflow as the TPS is nearly closed to generate the -10.5 psi of idle vacuum you are no longer using as a source. Being generated by the very same down stroke the pistons are doing, but in this case, at the top. All this takes place well into past the peak torque point at which cylinder pressures peak and equalize only once the TIP has enough boost created at the charge pipe to overcome the entire engines restriction to vent positive pressure, let alone the entirely useless baffle system you have added on top of it.

Something like that.

 

[Mosquito]

See. Science says it is inevitable for you to have seals fail because they are being constantly tested. You are actively ageing your seals by having them deal with positive pressure.
Crankcase, Oil Pan, RMS. Cam Magnets, Timing cover, Spark Plug o-rings, Cam Cradle, Oil Cap, etc. They are all part of the visible symptom. Some just fail faster than others.

 

[JerseyDrew77]

Cylinder pressure, blowby, volume displacement within the crankcase by the down stroke. After the volume is filled with pressure, it gets pushed out through the balance shaft, up the crankcase vent and in reverse through the oil drain ports on the cam cradle, eventually through the APR baffle plate, to the CC, through all 6 baffles and to a TIP that is nearly stagnant in airflow as the TPS is nearly closed to generate the -10.5 psi of idle vacuum you are no longer using as a source. Being generated by the very same down stroke the pistons are doing, but in this case, at the top. All this takes place well into past the peak torque point at which cylinder pressures peak and equalize only once the TIP has enough boost created at the charge pipe to overcome the entire engines restriction to vent positive pressure, let alone the entirely useless baffle system you have added on top of it.

Something like that.

So what your saying in layman's terms is that the baffled plate is what is causing that 0.1 - 0.2 psi of positive pressure.

 

[Mosquito]

So what your saying in layman's terms is that the baffled plate is what is causing that 0.1 - 0.2 psi of positive pressure.

No. Not necessarily and I am personally not concerned with the number on its own. All I care for is that a system that was designed to function in vacuum is being made to run out of it in ambient and positive pressure. The amount of restriction only makes things worse. The TCR system is rather basic but smartly put together, for a vehicle that sees consistent maintenance all around.

 

[DerHase]

Ok, so how does the APR plate create this slightly positvie pressure at idle and did it create more under acceleration?

On the contrary at WOT with the turbo spooled it generates about 5inHg (nearly 2x as much as the couple OEM PCVs I've tested). It bobbles around 0-0.1psi pretty much any time the turbo isn't spooled. Which on a street car... is majority of the time. It only generates a vacuum at the TIP when there is a ton of air rushing past it.

As @Mosquito said though, keeping ANY pressure on the crankcase is bad. It's a very slow failure as it's constantly testing your seals. If you have a low mileage motor, and all seals in great shape, you may not have any symptoms for a little while. Say 10-20k miles. If you had any seals that are borderline, you'll know a bit quicker.


The reason all the aftermarket plates put pressure on the crankcase at idle/low load situations is because they block off the only vacuum source that is present under those conditions. This is covered in the video. Fwd to the "How the stock system works" chapter at ~2:38 if you don't want to watch the whole thing. The "blue path" as I refer to it is completely blocked off at all times by all the existing PCV plates.

The PCV plates are a great solution - for a track-only car. I wouldn't be dicking around with the MK8 PCV if I had a trailer. But I drive the car to events, and on the street pretty regularly.

 

[yakboyslim]

The reason all the aftermarket plates put pressure on the crankcase at idle/low load situations is because they block off the only vacuum source that is present under those conditions. This is covered in the video. Fwd to the "How the stock system works" chapter at ~2:38 if you don't want to watch the whole thing. The "blue path" as I refer to it is completely blocked off at all times by all the existing PCV plates.

At least in my case I was smoking under hard braking, entirely because of this. Huge smoke clouds as oil was sloshing forward and getting sucked into the manifold under vacuum, but never had a drop of oil in my catch can, let alone my TIP. The APR fixed that by killing that entire pathway, but cars have PCV for a reason, and that pathway is the primary one during normal driving.

Seals aren't designed for positive pressure. Doesn't mean they can handle none, just means they weren't supposed to. My car wept oil from the normal places (oil cap, cam magnets, etc) but it did that before any catch can, and it hasn't seemed to get any worse with APR (if anything seemed to get better, but there is no reason for that to make sense), so who knows.

 

[PerceivedShift]

All that said, my holes-drilled MK8 PCV was put on and drove the car around last night with no ill effects. Normal ~1.5inHg vacuum at idle. Pulling from the cam cover in addition to the oil port might be a way to keep oil in the bottom end.

My non modified valve does have a tiny bit of oil residue in the intake port. I have no doubt they all ingest a tiny bit of oil stock, as long as it's not enough to matter it's fine though. This is after sitting the valve on its side for 20 min while I installed the modified one. Had an oil film but no apparent accumulation on initial removal FWIW.

Maybe I missed this earlier, what is the purpose of the newly drilled holes?

 

[DerHase]

Maybe I missed this earlier, what is the purpose of the newly drilled holes?

The primary problem of the OEM PCV is sucking up oil.

Oil will only be forced/sucked up the block passage if there is a considerable pressure differential. (Pressure in bottom end, vacuum up top in the PCV).

Where I put some holes, allows the PCV to pull vacuum on the valve cover as well (because it does not in stock form, it draws through the passage directly on the bottom end, and eventually vacuums the valve cover via near the timing chains, oil return ports, etc).

If pulling a vacuum on two places, fluid will only be pulled upwards if BOTH are submerged. I suspect the block passage gets fully blocked by oil sloshing, which in combination pulls it up. Apparently for some people the MK8 AOS is not enough to do the oil separation efficiently. OR @GTIfan99 is correct and VW just can't manufacture these things to save their life.

Pulling vacuum in both spots should cut down any chances of slurping oil considerably. It MAY also have the added bonus of allowing oil to drain before it ever makes it to the diaphragm.

Realistically, I'm sure everything going on inside is a chaotic aerated mess, but IMO the reasoning is sound.