Let’s talk PCV systems.

[Bonearzt]

Hi All, fairly new lurker with a 74 C-10 and a hopefully not TOO dumb question...
Is there any problem running 2 pcv valves, 1 on each valve cover?
Or is a breather cap on one side a better option?

Thank you!!
Eric

 

[Sad Sack]

Good question and I as well will be watching the replies. Was thinking about putting purty chrome valve covers on mine but was gonna keep it in line with stock setup so I’ll sit back and wait for responses. One cover with oil input and one with pcv was how I was told on OE pcv engines.

 

[dd1990]

Hi All, fairly new lurker with a 74 C-10 and a hopefully not TOO dumb question...
Is there any problem running 2 pcv valves, 1 on each valve cover?
Or is a breather cap on one side a better option?

Thank you!!
Eric

On stock engine one valve cover has pcv with vacuum and the other is fresh air from air cleaner or breather. If you do two vacuum pcv's, too much vacuum in the crank case can suck in the engines gaskets and cause leaks. Two breathers (no vacuum) and you might build up to much pressure in crank case and cause leaks, and oil leaks out of breathers and out on road.

 

[75gmck25]

With a stock system the PCV valve is in one valve cover and the hose running to the carburetor base is pulling air through the PCV. In the other valve cover you need a to let air into the engine, which is then sucked through the crankcase to the PCV in the other valve cover. The original GM setup ran the breather hose up to a small filter in the side of the air cleaner, but you could use a push-in breather in the valve cover instead.

Using 2 PCV’s or 2 breathers makes no sense, since you need to have air in on one side (breather) and air out on the other (PCV).

 

[Turbo4whl]

Good question and I as well will be watching the replies. Was thinking about putting purty chrome valve covers on mine but was gonna keep it in line with stock setup so I’ll sit back and wait for responses. One cover with oil input and one with pcv was how I was told on OE pcv engines.

Yes, like this ^^^ and the oil fill cap has the breather.

Only engine I know of that had 2 PCV valves was the GMC 305 V6. Under the sealed valve covers, one screwed into each head. Oil fill tube in the intake manifold casting with a vented cap. This engine also had the spark plugs on the intake manifold side of the heads.

Is there any problem running 2 pcv valves, 1 on each valve cover?

PCV valve is a controlled vacuum leak into the base of the carb. That valve is a match for the carb. 2 valves, the carb will be lean. That 305 V6 had very small valves, together they matched the carb. What would be the external hoses on other engines, the 305 had the system move air through the manifold.

 

[Bonearzt]

Thank you All!

 

[xm20k]

Unless its heavily built and does not pull much vacuum due to the cam having a ton of overlap stick with one PCV and one breather because you could cause the opposite problem of no PCV blowing gaskets out and causing oil leaks but instead sucking the gaskets into the engine like the ones on the China walls and causing internal damage if they end up in the pump or bearings.