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If I put my hand on the oil filler tube when my car is at idle I can feel a strong vacuum coming from the PCV system. Even when I remove the PCV valve I still don't feel any pressure coming from the valvecovers.......nothing wrong with that I guess !!
But when I remove the oil filler cap of my 4 cylinder "modern" Toyota there is pressure coming out from under the valve cover. This has nothing to do with the age or milage of the engine because I did this with several other modern cars and I had the same effect. "Nothing wrong with that" according to every modern car mechanic.
Can anyone explain me the difference in "valve cover pressure" between these modern engines and my old 289 V8 which had a rebuild some 50000 mls ago ? Has this anything to do with the PCV system ?

Erwin, The Netherlands,

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In the older PCV systems manifold pressure (vacuum)is routed to the valve cover via the PCV valve...the opposite valve cover is vented to the atmosphere via the air cleaner or a dedicated filter. So, filtered air is sucked through one valve cover through the engine and crancase to the opposite valve cover drawing crankcase vapor with it the vapor then goes through the pcv valve into the manifold and is burned with the intake charge.

Newer cars tend to vent the crankcase and fuel tank to a charcoal canister, vapor is trapped in the canister when the engine is not running. When the engine is running and there is manifold vaccum there is an electronic valve called a "canister purge valve" or "canister purge solenoid" that opens and vents the canister to manifold vaccum drawing the vapor out of the charcoal canister and into the manifold where it is burned with the intake charge.
 

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Good explanation. I do know if you feel air coming out of the oil fill hole of a 289, it may be because of blowby by the piston rings. Not a good thing. A healthy 289 has a bit of suction at that point (at idle).

Regards,

Dean T

Shikatta Ga Nai - "It cannot be helped"
 
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