PCV valve - 2001 Forester w/ 117k miles

[Wade]

Thanks, Steve,

for the earlier post on where to access the PCV valve on my
friend's Forester; I have not yet taken the time to replace it.
My question is:
How often is it recommended to replace it? What can happen if it's
never replaced?

I replace it regularly on my Accord [which is very easy to get to], so
I
don't know what happens if you never replace it.
I would guess a lot of folks never replace them.

Thanks,
Wade

 

[Bob Noble]

pvc valves are mostly a one way valve and also shuts off when your engine
goes to idle. If they fail, your engine would likely idle rough or not idle
at all. They do not need to be replaced often at all. Waste of time and
money.

They are replaced, because most people don't really understand what they do.
They mostly keep the engine from sucking too much vacuum at idle and causing
it to die.

 

[S]

Hi Wade!

Thanks, Steve,

for the earlier post on where to access the PCV valve on my
friend's Forester; I have not yet taken the time to replace it.
My question is:
How often is it recommended to replace it? What can happen if it's
never replaced?

I replace it regularly on my Accord [which is very easy to get to], so
I
don't know what happens if you never replace it.
I would guess a lot of folks never replace them.

Thanks,
Wade

Well, I certainly don't go out of my way to replace them, but they
typically aren't expensive (~$5), or difficult to get to.

The PCV system is almost entirely an emissions thing. Leakage past the
piston rings will tend to pressurize the crank case. As long as this
"blow-by" gas has _somewhere_ to go (i.e. the atmosphere), the engine
is happy (but the greenies aren't ;-). Modern PCV systems route this
blow-by back thru the intake, where it theoretically is burned
clean(er). As the blow-by gas contains oil mist, as well as water
vapor, and combustion byproducts, it will leave nasty deposits in the
intake, particularly on a well used engine.

I would imagine that if these deposits accumulated to the point where
the PCV valve became plugged, it could cause oil loss and eventual
crankshaft seal failure from the excess crankcase pressure. If stuck
open, it might cause high hydrocarbons in the exhaust, and emissions
test failure. Also, tho not usually the fault of the PCV valve, lots
of oil present in the exhaust can foul the oxygen sensor(s). By the
time an engine get's to the point where it is "burning" significant
amounts of oil (smoking), it's gonna need a lot more than a $5 piece
of plastic to be happy again.
PCV valves have a ball and spring arrangement that holds the valve
open when the pressure is equal on either side. Vacuum on the intake
manifold side will tend to close the valve. If you can feel the ball
rattle when you shake the valve, and it isn't too cruddy inside, it's
probably OK. Of course, by the time you get the darned thing in your
hand, you might as well re-install a new one . . .

Hope this helps. Try Wikipedia for a more detailed discussion.

ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

 

[StephenH]

Subaru's have a low fail rate on the PCV valve, the only ones i seen
fail were on bad overheat engines where coolant got into them, Don't
seem to cause the pressurization problems that Honda's get-plowing out
cam or balance seals.
Here is how I learned. I bought my car overheated/dead and I assembled
a engine. The result was oil consumption that required me to replace
the block again and rebuild one head again.
I now have a slight leak from the used pvc I installed, am planning to
replace it and the hoses soon.

 

[Wade]

Subaru's have a low fail rate on the PCV valve, the only ones i seen
fail were on bad overheat engines where coolant got into them, Don't
seem to cause the pressurization problems that Honda's get-plowing out
cam or balance seals.
Here is how I learned. I bought my car overheated/dead and I assembled
a engine. The result was oil consumption that required me to replace
the block again and rebuild one head again.
I now have a slight leak from the used pvc I installed, am planning to
replace it and the hoses soon.

Thanks, everybody, for the pcv info~!
I will replace my friend's when I find the time, no rush.
Wade

 

[ciercoleslore]

Hi,
often give many problems of these?

Thanks