Positive Crankcase Ventalation

[DINO_NO]

I have a breather on my valve cover rather than a PCV valve.
Could anyone fill me in on the pros and cons of having a breather rather than a PCV?

Thanks,
Dino

 

[G-MAN]

If you've got a 91 GM 3.1, I'm pretty sure you've got a breather on one valve cover and a PCV valve on the other.

 

[DINO_NO]

Thanks G-MAN, I did not notice that.

 

[DINO_NO]

Ah well, my other valve cover is out of reach, covered by the intake. That dosent help.

 

[mechtech2]

The breather is an INLET.
Air goes through the crankcase, then through the metered PCV valve, through a line, back to the intake manifold [to be re-ingested].
You need both, a breather and a PCV valve.

 

[SrDriver]

Keeping the PCV valve changed and hoses clean is a good idea.

 

[Gary Allan]

My jeep 2.5 has no PCV or metered orifice. It's the only engine I've ever seen without one or the other. The valve cover vent just routes to a large plastic plenum over the throttle body. It looks like it's designed to drain back to the valve cover. The 4.0 has a metered orifice with two ports to the valve cover ..the 2.5 ..only one. No other hoses are attached to the valve cover.

No apparent side effects from this setup. The throttle body is spotless.

 

[tom slick]

my old pontiac with a quad4 had no pcv valve.

it had a breather box with all of the breather lines plugged into it. there is nothing on a quad4 that is "normal".

 

[DINO_NO]

this is a V6, a little different than quad 4.
and still NOBODY has answered my original question.

 

[cowsareholy]

my 3.2 yamaha v6 also does not have a pcv valve and the throttle body is alway clean. i have taken apart the hoses that go up to the throttle body to clean it out and was also thinking of puting a catch can there to catch any oil and junk that does make it thru

 

[Gary Allan]

Quote:

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this is a V6, a little different than quad 4.
and still NOBODY has answered my original question.

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Your original question was:

Quote:

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Could anyone fill me in on the pros and cons of having a breather rather than a PCV?

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Since this is not your situation ..no one bothered. Those not equipped with PCV/metered orifice obviously have been designed with this in mind.

The PCV or metered orifice uses vacuum from below the throttle plate ...manifold vacuum. The PCV is a regulated manifold leak. It operates, with limitations, in proportion to engine speed. The metered orifice is a fixed manifold leak. The air supply is filtered in both. It's an "induced draft" to the crankcase with either the PCV or the metered orifice. My system, with only the vent above the throttle body, only gives some place for crankcase pressure to relieve itself. There should virtually be no vacuum above the throttle body. Maybe in terms of some fraction of inches of negative water column (I don't know ..but it won't read on a vacuum gauge).

 

[DINO_NO]

Thanks Gary, I'm still not sure if what G-man said was true or not.
I took the car into a place today and told them to change the PCV thinking they might know where it is, they said there is only a breather

 

[Gary Allan]

I think that they didn't want to change it ...or charge you the money required. Rockauto lists a PCV valve for the 91 3.1L in a GT and LE (I didn't bother with the SE).

 

[DINO_NO]

You were right with the LE, I guess it's just really hidden. I'm going to take it back now that I know it's there.

 

[falconman]

I remember on a similar GM 60* V6 the PCV valve was in the rear-facing valve cover, hidden under the the air intake. there was no room to get the PCV valve out, so I figured the intake has to come off to change it.

 

[Crashbox]

My '66 Chevelle 283 had an odd place for the PCV valve- IIRC it was in the rear of either the carb throttle body or intake manifold. Probably an easier factory location for it since it was first generation PCV as opposed to a draft tube.

 

[flatlandtacoma]

Quote:

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I remember on a similar GM 60* V6 the PCV valve was in the rear-facing valve cover, hidden under the the air intake. there was no room to get the PCV valve out, so I figured the intake has to come off to change it.

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They just figured you would change the PCV valve when you changed the intake manifold gasket?

 

[jorton]

Also if your PCV hose is leaking, or plugged up, you can have increased motor oil consumption or high idle.

 

[DINO_NO]

no consumption. yet.