How important is PCV valve?

Yesterday I replaced the PCV valve in my 98 OBL, probably for the first time in over 60K miles. The old one wasn't stuck but it did have a lot of crud inside, and the outside of it was pretty rusty. In just the first mile of driving I noticed that the motor seemed smoother, didn't hesitate and had more low-end torque (upshift points were lower RPM than before).

Is this just a placebo effect or could that $3 part make such a difference?

Thanks.

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BobN wrote:

Hi,

Don't know how much "blockage" your PCV really had, or if it seemed clean but was sticky, but yes, this is one place a $3 part COULD make a big difference. If it wasn't allowing enough flow thru the valve, excess crankcase pressure had to go somewhere else. Could have been "bypassing" thru other parts of the intake system, confusing some of the sensors and consequently the ECU. Totally clogged PCV valves CAN cause blowby. Not sure what the interval is for changing the valve on your car, but I think most of mine have suggested 30k miles. And, of course, the guys who sell the valves suggest 15k or so!

Glad to hear it helped!

Rick

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Rick Courtright wrote:

Can you translate this in to a basic definition of the function of a PCV valve? in fact, why is it called a PCV valve in the first place?

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PCV = Positive Crankcase Ventilation

kstahl wrote:

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kstahl wrote:

Hi,

Hope this isn't too simplistic:

Your crankcase builds up pressure as the engine's running. This pressure can come from "pumping" forces as the pistons go up and down just like a compressor (except that the pressure's built below the piston in this case as opposed to above it in combustion), and from blowby--compression pressure leaking down past the rings.

This pressure has to be relieved or the engine can blow seals, and who knows what else after that? Back in the dark ages when some of us were kids, engines had simple "road draft tubes" that were nothing but a tube generally coming from the valve cover area to vent all the pressure and attendant gases to the atmosphere.

Problem is the gases in the crankcase--oil vapors, combustion by-products, etc.--are pollutants. So sometime in the early 60's, mfrs started (spurred by legislative inputs, of course) installing PCV valves. The letters stand for "positive crankcase ventilation." The idea is that these various gases would still be vented, but thru a one way valve into the intake system instead of out to the atmosphere, thereby allowing oil vapors and such to be burned. In general, PCVs today send these vapors into the intake system after all the other sensors, so they're added directly to the incoming fuel mixture. The "positive" in the name is primarily a function of the way systems are designed with some kind of cross flow or scavenging mechanism so there's some fresh air flow throughout the engine, ensuring more of the "bad" vapors are pulled out. Earlier systems (like in the '60s) were "open," in that the air was often just pulled in thru a breather on the oil filler cap or a similar source, then vented into the intake thru the PCV. Today's systems are generally more "closed" in the sense they get their intake air thru the air intake below the air filter and other sources.

If the PCV is plugged, pressure can build up in the crankcase. If it's not badly plugged, vapors MAY be sucked into the system upstream of the sensors, compromising their ability to function properly. In extreme cases, a PCV system could become so plugged there might be a serious blowby problem and blown seals, oil clogged air filters and other problems. Much of the potential damage is a function of how the system's designed in the first place: some are designed more "fail safe" than others.

Not a complete story of PCVs, nor 100% accurate, but I hope it helps.

Rick

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i thought pcv valves were much more expensive. where did you buy this part for $3?

time

difference?

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At the local Autozone. Purolator brand. Looking at how it is made, that price makes sense to me.

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