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850 Turbo PCV / PTC question

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

Nick777
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850 Turbo PCV / PTC question

Post by Nick777 » Thu Nov 14, 2019 6:36 pm

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.



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abscate
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Re: 850 Turbo PCV / PTC question

Post by abscate » Thu Nov 14, 2019 7:52 pm

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


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Nick777
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Re: 850 Turbo PCV / PTC question

Post by Nick777 » Thu Nov 14, 2019 8:16 pm

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?



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Re: 850 Turbo PCV / PTC question

Post by abscate » Fri Nov 15, 2019 12:17 am

Nick777 wrote:
Thu Nov 14, 2019 8:16 pm
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


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Re: 850 Turbo PCV / PTC question

Post by Nick777 » Fri Nov 15, 2019 12:21 am

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
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Re: 850 Turbo PCV / PTC question

Post by Nick777 » Fri Nov 15, 2019 12:44 am

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!



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Re: 850 Turbo PCV / PTC question

Post by abscate » Fri Nov 15, 2019 12:48 am

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”


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Re: 850 Turbo PCV / PTC question

Post by jreed » Fri Nov 15, 2019 5:20 am

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

:)


1997 855 GLT (Light Pressure Turbo) still going strong. Previous: 1986 240 GL rusted out in '06, 1985 Saab 900T rusted out in '95, 1975 Saab 99 rusted out in '95, 1973 Saab 99 rusted out in '94

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Re: 850 Turbo PCV / PTC question

Post by abscate » Fri Nov 15, 2019 5:25 am

abscate wrote:
Fri Nov 15, 2019 12:17 am
Nick777 wrote:
Thu Nov 14, 2019 8:16 pm
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


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