850 Turbo PCV / PTC question

Nick777 · Post by **Nick777** » 14 Nov 2019, 18:36

Ok so I've researched this question on this site, but after say 20 min of looking I can't find a direct answer so:

By my analysis of the 850 Turbo PCV system, THE ONLY path by which crankcase vapors / crankcase pressure is relieved is via the path following the driver's side top mounted hose on the oil separator box, and that hose travels and finally releases into TWO outlets which are both elements of the PTC valve: (1) the intake hard pipe directly before Turbo, and (2) the vacuum line which goes to the intake manifold.

Since the (1) Turbo hard pipe outlet path is connected BEFORE the Turbo, the pressure in that pipe is very near atmospheric pressure. Furthermore (2) the vucuum to intake manifold path will always naturally be LESS than atmospheric pressure (if there are no vacuum leaks). Now since the crankcase is ALWAYS at greater than atmospheric pressure, the crankcase will preferentially vent to vacuum, but some will vent to atmosphere (Turbo intake pipe) as well.

Q1) if this is right, can you guys tell me if the PTC orifice is located BEFORE the vacuum oulet (i know the orifice is definitely located before the Turbo pipe outlet)?

Q2) if the answer to Q1 above is yes, than a clogged PTC orifice could give ALL of the same symptoms as a clogged oil box and/or hoses, correct?

Lets stop there.

Post by **abscate** » 14 Nov 2019, 19:52

Go back to your analysis with these facts

1 at idle, the intake manifold is a high vacuum, about 16 inches of mercury, the snorkel is near atmospheric pressure

2 under boost, the snorkel is at vacuum, the intake manifold is at 12-13 inches of pressure

Nick777 · Post by **Nick777** » 14 Nov 2019, 20:16

I see.

So you're implying that at idle, the PCV vents to the intake manifold but at boost the PCV vents to the Turbo intake?

Post by **abscate** » 15 Nov 2019, 00:17

Nick777 wrote: 14 Nov 2019, 20:16 I see.

So you're implying that at idle, the PCV vents to the intake manifold but at boost the PCV vents to the Turbo intake?

Exactly.

The PTC also isn’t a valve, it’s just a hole. It needs to be open and checked every 50k miles for blockage

Nick777 · Post by **Nick777** » 15 Nov 2019, 00:21

Yeah I suppose its just easier to refer to it as a valve even though it isn't.

Just to confirm, the ONLY pathway by which the PCV systems vents pressure is in fact via the PTC and only via the PTC, correct (one pathway is the intake manifold and the other is the Turbo inlet pipe) ??

Nick777 · Post by **Nick777** » 15 Nov 2019, 00:44

Sorry. I missed where you said "exactly", which of course implies that the PCV does in fact only vent pressure via the two pathways provided by the PTC.

Thank you!

Post by **abscate** » 15 Nov 2019, 00:48

The PTC is one path,the intake banjo bolt the other.

Both suck on the oil trap box to empty the vapors, but the intake manifold path doesn’t involve the PTC

Kudos for drilling into derp understanding on this stuff. That pays off in many things

If you really want to drill into the PTC, Jason took one apart a few years ago here

You can finds his thread by searching for “ barium titanate”

Post by **jreed** » 15 Nov 2019, 05:20

Here is the little write-up of the tear-down:
viewtopic.php?t=68898

Post by **abscate** » 15 Nov 2019, 05:25

abscate wrote: 15 Nov 2019, 00:17
Nick777 wrote: 14 Nov 2019, 20:16 I see.

So you're implying that at idle, the PCV vents to the intake manifold but at boost the PCV vents to the Turbo intake?
Exactly.

The PTC also isn’t a valve, it’s just a hole. It needs to be open and checked every 50k 30k on high mileage cars miles for blockage

Amended