Does the type of valve cover vent / breather make a difference - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**IT Cowboy** · 03-10-2025, 09:28 PM

I have valve covers with a vent on the passenger side and a PCV on the drivers side. The vent side is just a chrome capped push in type that goes into a 1 incg grommet. Is there a difference in these, can they become clogged and do the open K&N style work better or worse or do they all pretty much work the same by letting air in and just pick one.

geezer#99 · 03-10-2025, 11:04 PM

If you think it’s dirty just blow some air thru it.
I had one once that had a small plate left inside.
Do you suspect a pcv problem?

**IT Cowboy** · 03-10-2025, 11:25 PM

No real problems per se except I am seeing some vapors on warm up. I think it is the normal amount of blowback, oil vapors or just condensation cooking off. My pcv valve sucks like it should and I have a slight vacuum through the dipstick when running and removed. I wondered if I was getting too much crankcase pressure but I think it is ok. I also am just wondering if the current intake breather is clogged or dirty. Again it is the chrome mushroom type with the vent intake holes on the bottom.

Oh, my valve covers don’t appear to have any leaks either but I suspect the carb manifold gasket and linkages do have vacuum leaks.

geezer#99 · 03-11-2025, 08:13 AM

Where do you see the Vapor’s on start up and how are you measuring the vacuum at the dipstick?

**IT Cowboy** · 03-11-2025, 08:41 AM

Quote:

Originally Posted by geezer#99

Where do you see the Vapor’s on start up and how are you measuring the vacuum at the dipstick?

I am seeing vapors only when initially warming up and it is near the valve covers and predominantly on the passengers side and near the manifold breather. I am still trying to narrow it down but it is only on initial warm up and I really think it is just condensation burning off. The afternoon temp here was only around 58 when I pulled it out of the garage to warm up. It looks like steam and there is no smell to it and is easiest to see when reflecting off the polished valve cover. I have UV dye in the oil and coolant and am not seeing any leaks with a UV light.

I am just placing my thumb over the open dipstick to verify that it is sucking in and made no formal measurement. I was a bit concerned with too much crankcase pressure and if it was breathing properly but I really think it is all just normal.

geezer#99 · 03-11-2025, 08:56 AM

Do a white glove test along the lip of the valve cover to check for leaks.
White cotton garden gloves work good.

Dead Parrot · 03-11-2025, 11:18 AM

Yes, breather filters can become clogged. Depending on type, some can be cleaned and others need replacing.

The OEM setups normally have the breather filter inside the main air cleaner housing so any excess blow by still gets burned by engine combustion.

It doesn't take much oil seepage from the valve cover gaskets to cause some start up smoke off the exhaust.

03-10-2025, 09:28 PM	#1
IT Cowboy Senior Member Join Date: Jan 2025 Location: Clarkdale, Arizona in a van down by the river Posts: 341	Does the type of valve cover vent / breather make a difference I have valve covers with a vent on the passenger side and a PCV on the drivers side. The vent side is just a chrome capped push in type that goes into a 1 incg grommet. Is there a difference in these, can they become clogged and do the open K&N style work better or worse or do they all pretty much work the same by letting air in and just pick one. __________________ 1972 C10 Custom Deluxe Highlander 402 2019 Toyota Tundra SR5 2018 Jeep Wrangler Sport Freedom isn't safe, it requires you to take responsibility for your own life, your own safety, and your own success. It carries with it the possibility of failure and the understanding that you're working without out a safety net. If you give the state the responsibility for any of these you also give up the freedom that accompanies the responsibility.

03-10-2025, 11:04 PM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,787	Re: Does the type of valve cover vent / breather make a difference If you think it’s dirty just blow some air thru it. I had one once that had a small plate left inside. Do you suspect a pcv problem?

03-10-2025, 11:25 PM	#3
IT Cowboy Senior Member Join Date: Jan 2025 Location: Clarkdale, Arizona in a van down by the river Posts: 341	Re: Does the type of valve cover vent / breather make a difference No real problems per se except I am seeing some vapors on warm up. I think it is the normal amount of blowback, oil vapors or just condensation cooking off. My pcv valve sucks like it should and I have a slight vacuum through the dipstick when running and removed. I wondered if I was getting too much crankcase pressure but I think it is ok. I also am just wondering if the current intake breather is clogged or dirty. Again it is the chrome mushroom type with the vent intake holes on the bottom. Oh, my valve covers don’t appear to have any leaks either but I suspect the carb manifold gasket and linkages do have vacuum leaks. __________________ 1972 C10 Custom Deluxe Highlander 402 2019 Toyota Tundra SR5 2018 Jeep Wrangler Sport Freedom isn't safe, it requires you to take responsibility for your own life, your own safety, and your own success. It carries with it the possibility of failure and the understanding that you're working without out a safety net. If you give the state the responsibility for any of these you also give up the freedom that accompanies the responsibility.

03-11-2025, 08:13 AM	#4
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,787	Re: Does the type of valve cover vent / breather make a difference Where do you see the Vapor’s on start up and how are you measuring the vacuum at the dipstick?

03-11-2025, 08:56 AM	#6
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,787	Re: Does the type of valve cover vent / breather make a difference Do a white glove test along the lip of the valve cover to check for leaks. White cotton garden gloves work good.

03-11-2025, 11:18 AM	#7
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,675	Re: Does the type of valve cover vent / breather make a difference Yes, breather filters can become clogged. Depending on type, some can be cleaned and others need replacing. The OEM setups normally have the breather filter inside the main air cleaner housing so any excess blow by still gets burned by engine combustion. It doesn't take much oil seepage from the valve cover gaskets to cause some start up smoke off the exhaust.



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