MK8 PCV Crankcase Datalogging: Basic vs Full Retrofit
Correction to the last post, and a whole slew of new data
I was not really planning on releasing another video quite so soon, but wanted to clarify an error on my part… And since it was a long holiday weekend, I used it to my advantage to establish procedures going forward, plus verify some of the more crude gauge-and-video based testing that has already been done.
Reviewing videos and looking at my Matco vacuum gauge, when I was taking the "shorts" in the dark recently (measuring vacuum at the TIP via the Tiguan hose top fitting), I was reading the cmHg scale... Not inHg.
All INITIAL testing done up until now - clarified with conversions of all units.
So what does this mean? It means the TIP is a LOT closer to the (OEM targeted) operating pressures of the crankcase. Making any changes that reduce the TIP vacuum means the crankcase will be operating a LOT closer to ambient (or positive) pressure than originally thought.
This does change my theory on WHY the PCV is ingesting oil.
While it still MIGHT be related to position of the diaphragm under load (as alluded to in my last post/video), it could be as simple as there just isn't enough vacuum source available. This would result in the crankcase seeing pressure when a TIP and/or intake are changed out… causing oil to push upwards.
In a nut shell I added a crankcase pressure sensor to my data gathering capabilities, so I could revisit all of these theories and not just get peak values, but observe crankcase pressure and PCV sensor (vacuum source) pressures dynamically over the entire rev range (and in transient conditions). Here is a chart of all the instrumented testing done, primarily for checking various boost levels, and the effects of the Venturi.
Results summarized. This is all reviewed in the video above along with direct observations of multiple data logs as well.
So we’ve determined a few very important things with this baseline instrumented testing:
Using a gauge at the Tiguan PCV top port is VERY relevant, which means YOU can perform this type of testing very easily as well. It also validates all prior gauge-based testing (with the units read correctly of course).
The crankcase operates at -0.9 to -1.1psi roughly. This is because the diaphragm acts as a regulator and lowers vacuum to this desired level. Obviously you must have a higher vacuum source (the turbo inlet pipe) to maintain this crankcase vacuum under WOT.
Stockish boost levels results in a -1 to -2.3psi or so vacuum pull at WOT (from 4k-6k) from the turbo inlet pipe (basic retrofit). Peak of about -2.5psi up near redline.
The turbo inlet pipe-equipped car that I gauge tested only showed -2.5cmHg, which equates to about -0.5psi at WOT. This is 50% of what needs to be in the crankcase… So there is a very real possibility that the crankcase may be operating under pressure, at least down low in the RPMs. If you watch the video closely, it appears the needle doesn’t even start to move until about 4500rpms.
Next step: Swapping some turbo inlet pipe(s) and intakes between some different cars to finally put that theory to the test… plus see that IF there is a problem with reduced vacuum for the PCV system, can the Venturi fix it? My money is on “yes”.
