Thread: Pommie Provent

Ha, I bet that was a chore!

Originally Posted by BennehBoy

Could this be because the oil drain was open to air, therefore there was no suction on the underside of the filter?

It's my guess that there is a delicate to and fro balance between blow-by gasses pushing into the Provent and the vacuum pulling them out.
Most of the time, there will be a steady flow in the obvious direction and I believe that the system is designed to maintain a bit of vacuum in the crankcase most of the time. This is what 'Positive Crankcase Ventilation' means. It works quite differently (and, probably better) in non-turbo engines, but the effect is the same.
The thing is, sometimes, there is more blow-by that others and sometimes, there is more vacuum than others. If blow-by and vacuum increase at the same time - nice - everything works well. The Depression Control Valve (that's the $50 plastic widget with 'TOP' written on the top - wtf?) is there to stop any madness taking place if things go out of whack. I believe that there is a device in the outlet of the Provent, which is designed to do exactly the same thing, and that the DCV can be discarded, once you fit a Provent, but don't take my word for it until I have wasted $50 (I'm going to take one for the team) and tested the crankcase vacuum with a new DCV, with the new DCV with a new Provent - and with the Provent only - I'll post up the results before Christmas.
Anyway, back to my point. If the Provent vents to atmosphere (through its 'drain' hole at the botton), you've got no chance of maintaining Positive Crankcase Ventilation, and you might as well simply vent the rocker cover to atmosphere - on second thoughts, that's exactly what you have done.
You've also given atmospheric air access to your turbo without first passing through your air cleaner or, more importantly, through your MAF, so the engine doesn't know it's getting in and the ECU can't regulate your fuel properly so all bets are off regarding smoke, performance, efficiency - you name it.
My Provent came with an optional cheap plastic tube about 2 feet long with a good-quality tap on the end, to allow periodic bleeding of waste oil, but no air in or out. I'm going to use it.
Thanks a lot to the OP for the great description and the clear photos. that's exactly how and where I'm going to fit mine (I've already got the brass reducers and a 90 deg. brass bend, in case I can ditch the DCV).

Just to reinforce your comments, I added a sealed oil catch can to the drain feed of the provent a couple days after the initial fitment.

Now that I've fixed the underlying problem that I'd hoped the provent was going to help with (namely a broken cylinder head, oops!), I'll put the provent and catch tank back in line so they can operate as they were intended.

Should save me having to flush the intercooler out for quite a while I hope!

Thanks for your post.

Here's what it all looks like one full engine rebuild later!



Bit cleaner than before

Originally Posted by BennehBoy

Bit cleaner than before

Dude, you're hurting my eyes

Re the manifold depression valve. It's function as far as I can see by pulling it apart is to CUT OFF the flow of crankcase gas under high or even moderate boost when there is relatively high vacuum in the inlet before the turbo. It allows flow when there is low vacuum in the inlet manifold ie at idle or cruise. It doesn't appear to react to high crankcase pressure .
I may not know the whole operation, but it would close when sucked from the manifold side but not when blown into from the crankcase inlet.
Regards Philip A

Originally Posted by PhilipA

Re the manifold depression valve. It's function as far as I can see by pulling it apart is to CUT OFF the flow of crankcase gas under high or even moderate boost when there is relatively high vacuum in the inlet before the turbo. It allows flow when there is low vacuum in the inlet manifold ie at idle or cruise. It doesn't appear to react to high crankcase pressure .
I may not know the whole operation, but it would close when sucked from the manifold side but not when blown into from the crankcase inlet.
Regards Philip A

Yup but it will also open up under high boost when crank case pressure equalizes the boost 'suction' - I guess the main purpose is to stop a massive pressure differential causing high vac in the engine.

Originally Posted by BennehBoy

Here's what it all looks like one full engine rebuild later!

One full engine rebuild? More like One and a Half engine rebuilds.

I bought a set of those Roose Motorsposrts hoses too, as my OEM MAF to Turbo hose split, and I couldnt find a Silicon alternative in Australia.

I opted for low-ley Gloss Black tho