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
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.
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
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
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