ok, so I cleaned the PCV valve...

We've been through all this before - I guess it just got left dangling.

I know (think ?) we agreed that the PCV is a metered air leak. How can it
not affect engine efficiency and therefore fuel mileage? BTW I'm quite
sure that a PCV can fail in more ways than getting plugged up - e.g. the
spring can get gunked up and bind. The PCV lives an environment which is
not kind to metal or even plastics.

I'm quite sure that the reason the rubber plug at the end of the exhaust
camshaft of an Integra, next to the distributor, gets pushed out is because
of crankcase pressure increase. It seems to happen more in Winter when the
PCV can get frozen up.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

 

if you wanna be safe and not necessarily "ecologically correct", im sure
you could get a second oil cap and put some kind of foam filter or valve
tapped into it for good measure

swap it back for the biennual smog check tho!

 

Because the air and blowby is coming from, and going to, the SAME PLACE AT
ALL TIMES.

Go take a good hard look at your own PCV system. See where the crankcase
takes in air. See where the PCV valve dumps its air. Notice that BOTH are
located in the INTAKE tract, mere inches from each other?

There is NO "air leak".

The valve does NOT introduce new air into the system.

It simply meters the existing air so as to ensure that there is POSITIVE
flow through the crankcase, resulting in a constant changeover of the air
in the crankcase, with any blowby gases routed back through the combustion
chamber again.

A blocked PCV Valve but a free breather will cause the gases to cavitate
inside the crankcase. Since the breather will be under slight depression
from the intake tract, pressure will be higher in the crankcase than the
intake, so excess gases will get pushed into the intake and recycled
through the combustion chamber again, just as if they went through the PCV
properly, but there will be be no positive flow.

The main purpose of the PCV valve is to ensure that one end of the breather
system always has a lower pressure than the other, so that one end will
always be an intake, and one will always be an outlet. That is why it has a
variable orifice.

How is this different from being "plugged up"?

The PCV plunger is surrounded by the spring. The metered orifice is the
SPACE around the coils of the spring. If the spring gets gunked up, then
the orifice is reduced, becuase the orifice IS around the spring.

And it is made of metal and oil-compatible plastics. You don't think they
would think of doing that?

It happens because the rubber gets old and has reduced holding power,
especially when cold. It is only really clamped in place by the two little
ridges on it anyway. This explained to me by my Japanese mechanic. I
replaced my leaky old one a few years ago. It has not leaked since.

In order for pressure to build to the point where it could possibly "push
the plug out", BOTH the PCV AND the breather MUST be blocked.


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(y_p_w) spake unto the masses in

The PCV *SYSTEM*, or the PCV *VALVE*?

Your quote does not say.

If the PCV *system* is malfunctioning, then definitely those symptoms may
be caused. Such as if the breather hose is cracked or disconnected. Such as
if the PCV valve grommet has perished and is letting air in around the
valve stem.



I am starting to suspect that posters here are thinking that the "system"
consists of the valve alone.


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Wrong. Totally incorrect understanding of the PCV system.

And even if plugged, a PCV valve will NOT affect mileage.


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I just asked my mechanic, who has specialized in Japanese cars for 40 years
and has run his own shop for the last twenty (no, from 1980, so 24 years).
He does everything up to and including rebuilding engines and
troubleshooting electronics problems.

He says a plugged PCV valve will definitely NOT affect gas mileage. End of
story. The computer would compensate for any metering incorrectness
resulting therefrom.

That makes three *actual working mechanics*, all with many years of
experience, who have told me that a plugged PCV valve WILL NOT affect gas
mileage.


Caroline's many instances of Google results are WRONG. Plain and simple
WRONG. "Internet legends" is what they are. WRONG. Misleading.




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What year was this written? Years ago, Honda never even
bothered with PCV valves because minor dirt in PCV valves
would cause major problems with air mixture in carburetion.
In fact I am surprised Honda has even gone to PCV valves.
1980s Hondas never used PCV valves. Hondas has a superior
alternative design. But then with fuel injection, changes in
air bypass do not adversely affect air mixture. Throttle is
just another source of air leakage in a fuel injected system.

IOW that text is probably correct when PCV valves were
connected to carburetors. It does not apply to fuel injected
system.

Alan - don't worry about the PCV valve. The valve does
exactly as you have described. If a valve is so clogged as to
cause crankcase ventilation problems, then the engine has far
more serious problems than a clogged PCV valve.

 

Yes, mine failed "open" (94 del Sol Si). When I pinched the hose
at idle, there was no click and the idle changed. If it had been
plugged, there would also have been no click, but the idle would not
have changed.

 

Of course it does. A fuel injection system has to know the mass of air
being sucked into the combustion chambers to meter the fuel accurately.
Compensation has to be built into the ECU rules for the metered air leak of
a PCV valve.

There are lots of ways things can go wrong and several variables. Have
ever taken a PCV valve off and looked down the tube coming from the
breather box? Try it in Winter and you'll see a coating or clog of
emulsified oil down there depending on whether the valve is functioning
properly.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

 

Look I don't really care what your mechanic says. I've been told enough
guff by mechanics over the years to fill an encyclopaedia.

The computer hasn't measured the mass of leaked air - it doesn't know about
it other than some fixed compensation curve built into the engine parameter
profile... based on a properly functioning PCV valve.

So your mechanics are right and the auto mfrs and engine designers are all
wrong.<shrug>

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

 

Nope; dead-on correct.

For the rational among us trying to learn about pressure: Think of the crankcase
as a bucket of water being fed with a hose but also having two holes in the
bottom of it. The rate of water flow and the hole sizes are such that 4 inches
of water are maintained in the bucket with this setup. If one suddenly plugs one
of the holes, what happens to the water level in the bucket?

It goes up. Just like the pressure in the crankcase will be higher, on average,
with a plugged PCV valve.

Forgot to add that various Chilton's manuals also comment on how a
malfunctioning PCV valve may affect mileage. E.g. from the Ford Taurus/Mercury
Sable 1986-1992 Chilton Manual:

"Do not remove the PCV valve system from the engine, as doing so will adversely
affect fuel economy and engine ventilation with resultant shortening of engine
life." -- Emissions Controls, Page 4-6

Re your internet myth "theory":
Guess folks should ignore all the "internet wisdom" that says change your car's
oil every so often, too.

 

George Macdonald <fammacd=!SPAM^> spake unto the
masses in

So you throw the baby out with the bathwater. They're ALL bad, right?

It's NOT "leaked air". It's the very same air that has already passed by
the throttle plate and the air flow meter.

All the PCV valve does is make sure that flow is always present, and always
in one direction.

This is the part nobody in this group seems to understand. Of course,
nobody in this group is a working mechanic, either (me included). And some
of them aren't even willing to listen to what working mechanics have to
say.

Show me ANYWHERE where ANY auto mfr and engine designer says HOW MUCH the
engine will "run rich" with a plugged PCV valve.

I think you guys are all misunderstanding what those auto mfrs and engine
designers are saying. Web pages don't count here.



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Bad analogy. Water is not air. Water cannot change density. That's why
hydraulics work the way they do.

You're wrong, Caroline. So completely wrong you have no idea how wrong you
are. Even George is clueless here.

You should learn to read. It says not to remove the SYSTEM, which is
definitely bad for the motor. The valve is only one part of that system.

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"Caroline" <> spake unto the masses in

A much more accurate analogy:

Imagine a bucket with ONE hole in the bottom (NEVER plugged). Now make two
holes in the SIDE, one above the other, but both always submerged. Connect
a hose between the two side holes.

THAT's your PCV system, minus the valve itself.


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Maybe you guys should crosspost your discussion to rec.autos.tech and
see what some of the guys there say.

 

Are we talking a "Positive Crankcase Ventilation (PCV ) system. Nothing is
submerged or below any oil line. The PCV valve is simply a device that
meters the amount of air(crankcase vapour) the intake is allowed to suck
out of the crankcase, all well away from any pool of oil, and the other
hose is a supply of fresh filtered air being drawn into the crankcase ,
again above the oil, to replace the air that the PCV has drawn out.

 

The analogy has nothing to do with density. It has everything to do with mass
accumulation in a dynamic, fluid system.

BTW, water can change density. Indeed, in liquid pump calculations, the change
in density when moving a liquid such as water may have to be considered during
design.

non-rebuttal snipped

I have no problem with your unfounded opinion. But every time you spout here
that a malfunctioning PCV valve will never affect fuel economy, plan on facing a
rational explanation of why it may, along with a dozen or more citations of
greater repute than you, backing it up.

I too do not think much of putting out misinformation on Usenet.

 

= the breather hose (which is far far less likely to become plugged than the PCV
valve)

Presumably the level of water denotes the pressure of the gases in the
crankcase. (It does with my analogy.) Presumably in your version, the PCV valve
line is the hose connecting the two side holes.

Then you've got a PCV valve line whose intake is from the crankcase and whose
discharge is to the crankcase.

This is not the case for an actual PCV valve system. The PCV valve intake is
from the crankcase. Its discharge is to the air intake, very close to the
cylinders.

Your pressure relationships do not mimic those in an actual PCV system.

(PCV valve system here = the PCV valve and the hose from the breather chamber to
the PCV valve. This is the way many or all Hondas' PCV systems are set up. Other
cars' PCV hoses come off the valve cover.)

If you're going to consider this carefully, watch your mass flows, their phase
(liquid or gas), and when a chemical reaction (combustion) takes place to affect
pressure. Also, the fact that mass (air and fuel) enters the cylinders via the
intake valves but exits the cylinders via the exhaust valves *and* via blowby
past the pistons.

And since you loathe "Internet wisdom," here's Tom and Ray Magliozzi (yes, the
Car Talk guys), backing up what I have said:

-----
RAY: Blow-by occurs when combustion gasses slip by old, worn-out piston rings
and end up in the crankcase, where they don't belong. Actually, a small amount
of blow-by is normal and is easily expunged by the crankcase ventilation system.
But on old heaps (i.e., yours), worn-out rings can let so much stuff into the
crankcase that the ventilation system just can't handle it.

TOM: So the pressure in the crankcase builds up until gasses and oil try to
escape any way they can. And we often see air-filter housings full of oil, seals
blown out or leaking, and the occasional dribbling dipstick.

RAY: The solution is an engine rebuild, which would include a ring job. But
before you consider that route, or ditch the truck, I've got two other things
for you to try.

TOM: If you've lived a really good, clean life, your problem might just be a
plugged crankcase ventilation system. So have your mechanic check out your PCV
valve and the hose it's attached to. ...
-----
http://lang.motorway.com/home/articles/qandaoilydip.asp

Go ahead and knock two MIT graduates, both of whom worked in their own car
repair shop, and one of whom (Ray) has worked as an auto technician for some 30
years (and is still employed full time as such).

 

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"Caroline" <> spake unto the masses in



Note to Caroline: This time, please do not remove the cross-posting. I want
as many minds involved in this debate as possible.

You've got it backwards.

If our analogy is to be the bucket with a hole in the bottom, then the top
of the bucket is the throttle inlet and the bottom of the bucket is the
intake valve.

The PCV system has nothing to do with either the throttle or the intake
valve. It simply redirects some of the clean intake gas to the crankcase,
where it picks up blowby, and then directs it back to the intake again.

My anology (countering your erroneous one) has two holes in the side of the
bucket, both in the water, but one above the other with a hose connecting
the two. Absent the blowby, that IS a PCV system. It's just a redirector.

The PCV system does not go to a second intake valve, which is what you
conceptually imply with YOUR analogy of a bucket with two holes in the
bottom.

Neither do yours. Your bucket analogy consists of a non-compressible fluid
(water) being PUSHED into a container (bucket). The actual intake system of
a car uses a compressible fluid which is SUCKED into the engine.

The intake tract pressure is ALWAYS less than ambient with the engine
running. Hence, in a normal engine, there is ordinarily SUCTION at BOTH
ends of the PCV system. It is necessary to use a restrictor valve to lower
pressure at one end to make sure the flow is always in one direction.

That's the PCV valve.

Are you familiar with the venturi principle? That's all the PCV valve does.

It doesn't matter. The principle is identical, even on carbureted cars:

Hose from intake to from crankcase -> Hose from crankcase to PCV valve ->
PCV valve back to intake tract again.

<snip quotes from TV personalities saying that heavy blowby will overwhelm
the PCV system>


Well, yes, all undoubtedly true. But this has never been part of the
discussion. What has any of that got to do with your contention of
reduction in gas mileage from a plugged PCV valve? The Car Talk guys
haven't said that at all.


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