Originally Posted by viking
Im not talking about the pcv valve i have one and it works fine im talking about the oil breather cap.
OK, I'm confused now . . . what are you referring to as the oil breather cap?
I have a '74 Chevy with a 350 in it . . . on the driver's side, towards the front of the engine I have a pcv valve that inserts into the valve cover and hooks to a vacuum port on the carb. On the passenger side towards the front I have an oil fill cap where I put the oil into the engine. On the passenger side towards the back of the engine I have a metal tube that comes up and hooks to a rubber hose that runs to the bottom of the air cleaner -> this is what I refer to as the oil breather.
My understanding is that the pcv valve uses vacuum from the intake to suck the crankcase fumes out of the crankcase and into the intake so those fumes are burnt up in combustion rather than released to the atomosphere. This setup requires some air flow through the crank case to operate properly and the oil breather provides that. Since air is being sucked into the crankcase through the oil breather one wouldn't want dusty air to be sucked in and contaminate the oil so that breather is usually hooked up to the carburetor's air cleaner so that the air that is introduced to the crankcase has been through a filter. If you don't want that line running up to the air cleaner then you can remove that line and insert a small stand alone filter breather in the valve cover (remember to plug the hole in the carb's air breather).
The oil fill cap is just that - just an access to the engine through which oil is filled.
Hope that helps!