What is a PCV valve, and does it really need to be changed so often?

Dear Car Talk

Dear Car Talk | Apr 01, 1997

Dear Tom and Ray:

I have a '94 Camaro with 25,000 miles. Last week when I went in for an oil
change, the technician told me I needed to replace my PCV valve. He said GM
recommends replacing this valve every 6,000-9,000 miles. Since mine was
still original, he said it was way overdue. What exactly is a PCV valve,
and does it really need to be changed so often? Or was he just trying to
sell me a 50-cent part for $5? -- Rob

RAY: Well, he's not going to go very far as a rip-off artist pushing PCV
valves, Rob. If he really wants that 40-foot fishing boat, he's going to
have to switch over to something more lucrative, like, say, ignition
modules or seat covers.

TOM: In any case, PCV stands for "positive crankcase ventilation." When
gasoline is burned in the cylinders, there are always some vapors that get
past the rings and end up down in the crankcase. The PCV valve is what
allows those vapors to escape.

RAY: The PCV valve routes the vapors out of the crankcase and into the
intake manifold, where they get sent back into the cylinders and are
combusted along with fresh air and gasoline.

TOM: Every so often, the PCV valve does get plugged up and needs to be
cleaned or replaced. It takes just a minute to check it, and it's possible
that yours was plugged up at 25,000. But I've never seen a recommendation
from GM calling for a PCV valve change every 6,000-9,000 miles. That sounds
way out of line. As far as I know, they don't even recommend checking it
until 30,000 miles.

RAY: So if this mechanic has OCPCVD (Obsessive Compulsive PCV Disorder),
tell him he can check it every 5,000 miles when you come in for an oil
change. But unless there's evidence of a specific problem, he shouldn't
have to replace it again for at least 30,000 miles.

* * *

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