BITOG readers, educate Michael about PCV Valves!

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BITOGers, Please teach me about PCV valves. I'd like to learn: 1) The purpose of a PCV valve. 2) How does a PCV valve work? 3) How does a PCV valve relate to water contamination (i.e. water found in oil)? 4) Does/How does a PCV valve relate to sludge buildup in engines? 5) Why is the BITOG population so conscientious about checking their PCV valves frequently? Thanks, Michael
 
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Basically, all a PCV valve does is allow a certain amount of airflow through the crankcase of an engine to scavenge blowby gases and relieve crankcase pressure. The PCV is usually located on a valve cover. V shaped engines are easier to explain so I'll use that for an example. On one valve cover, you have the PCV valve with a vacuum line that goes to the intake. On the other valve cover, there is a larger diameter line that also goes to the intake; this is the fresh air side of the PCV system. The PCV side creates more vacuum than the fresh air side so the vacuum from the engine pulls air through the fresh air side, on through the crankcase, through the PCV valve, and into the intake manifold and then into the combustion chambers where the vapors can be burned. When vacuum is high (throttle closed or partly open at higher engine speeds), the PCV valve partially shuts from the high vacuum because not very much flow through the system is needed. When your accelerating hard, there is no vacuum, and the valve stays open all the way and allows maximum flow through the system when it is needed. The system is in place because blow by gases/moisture from combustion will form acids in the oil which equals sludge/oil degradation. Also, crankcase pressure, if unrelieved, will blow out oil seals and cause a power loss. Back in the old days, there was just a vent to the crankcase to relieve pressure, but a closed loop PCV reduces emmisions and pulls the acid forming vapors from the crankcase. Whooooooo, my fingers are tired now! [ April 16, 2005, 10:38 PM: Message edited by: Drew99GT ]
 
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Someone once told me that if you use synthetic oil (Mobil 1, GC, Redline, Amsoil).....it will keep the PCV valve cleaner. Is that true or just a B.S. 'mechanics' opinion ??? [I dont know]
 

JHZR2

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Id guss that if your oil hjad lower volatility, therewould be less oil-related gas to be scavenged by the engine through the intake. As a result the air going through would be cleaner, and thus the PCV valve as well. JMH
 
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quote:
Originally posted by JHZR2: Id guss that if your oil hjad lower volatility, therewould be less oil-related gas to be scavenged by the engine through the intake. As a result the air going through would be cleaner, and thus the PCV valve as well. JMH
mostly it is blowby and moisture also some oil vapor,If the vapor was oil the consumption would be incredable.
 
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quote:
Originally posted by LT4 Vette: Someone once told me that if you use synthetic oil (Mobil 1, GC, Redline, Amsoil).....it will keep the PCV valve cleaner. Is that true or just a B.S. 'mechanics' opinion ??? [I dont know]
yes because although most of the crankcase is blowby and water vapor the oil content turns to sludge like deposits . The more refined the oil or a Syn the less crud there is to form the sludge.
 
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I've only seen 1 PCV that was just a little crudded up and that was my moms Olds that had an internal coolent leak. The one in my Dad's truck is still original with 170K and works just fine; totally clean and rattles like a new one. As long as you maintain oil changes, I doubt you'll get any accumulation of crud in the PCV. I personally think all the commotion over changing them every 10,000 miles yada yada yada, is preventitive maintinence gone overboard. But hey, the peeps that make the valves don't mind [Wink] (aren't they the ones saying change it every 10,000 miles).
 
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quote:
5) Why is the BITOG population so conscientious about checking their PCV valves frequently?
I installed an OEM one from the Saturn dealer on my SL2, since there is a TSB saying an aftermarket one can contribute to oil consumption. It was cheaper then the one from Napa, but I don't know if it made a difference. I did run a few oil changes with Mobil 1, and could not believe how clean the PCV stayed, compared to the one with caked deposits that lasted 40,000 miles usning Castrol GTX. I changed mine with an OEM one on my 93 Sentra, since both the front and rear main seal are leaking. I just finished my 2nd Auto-RX rinse. So far, no change, but thought I would give it the best chance for reducing the oil seal leaks.
 
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