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Will running no PCV harm engine / gas milege?


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Apologies for the noob questions. I was working on my dime yesterday and notice that the PCV hose was cracked and no longer hooked to the Crankcase tube vent. Then I inspected the linkage to the valve and the previous owner had disconnected it and completely tied it down shut.


The car runs smooth as is, but I was wondering if adding the PCV functionality again will help give me some more HP, and gas mileage, and burns up less oil, since it reduces the pressure.


I ordered a new hose for 12 bucks and I just gotta find a pin or something to re-link it to the throttle linkage.

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The PCV valve uses a small amount of intake vacuum to suck crank case fumes (warm fuel and water vapor and combustion blow-by gasses getting past the rings) and runs them through the combustion chamber to burn them up. The air removed from the crank case is made up by filtered air from the breather on the carb and is drawn in through that hose on the valve cover. At idle and low speeds this is how it works. At higher speeds the engine vacuum is lower and the motor may produce more blow-by than can be drawn into the intake by the PCV valve. In this case the air reverses direction and flows out the valve cover hose and into the air filter housing where it is sucked into the carb.


The PCV valve is essential for removing water and gas vapors from the crank case where they would normally condense when the motor cooled. The PCV valve increases the time and mileage between oil changes by keeping the oil cleaner and free of contaminants and dirt for a cleaner motor.


I think the long and short of it is that it's not ideal to not have the PCV hooked up, but it won't harm the engine per se. The oil gets dirtier quicker, and it does weird things with blowby gases.


I'm not sure what you mean by having throttle linkage involved in the PCV system? The PCV is only a pipe coming out of the block connected by hose to a valve threaded into the intake manifold. The block should either be PCV vented or open vented. It should not be blocked off if this is the case.

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If the PCV is plugged, the pressure vents out the top breather. Usually by blowing oil all over the place, if you have moderate or worse blowby. If the top vent is plugged too, you blow out gaskets. Valve cover, oil pan, timing cover, etc. The pressure has to go somewhere.


So, folks go 1950s-tech and vent them to the road. Which coats the bottom of the car with oil. Even more concerning is if you park the car outside on a damp day. The hot but cooling engine will draw air in. If your vent line points to the road, it's pulling in nice humid air that's full of water. That gets in the oil, forming acid. That acid causes rust and bearing damage.


Which contributed to why 1950s engines lasted about 50,000-60,000 miles before being worn out.


A PCV hooked to the intake manifold not only keeps the heavily hydrocarbon-fouled crankcase gasses out of the air (which is why it's a pollution device) but when working provides a small vacuum to the crankcase, pulling in and burning off the blowby gasses, and circulating clean air in so that the gases never get the chance to acidify or otherwise pollute the oil.

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