valve cover breathers

[yogi_stvl]

when do usually use valve cover breathers? what good do they do?

 

[Michael Yount]

When an engine runs, some cylinder pressure leaks by the rings and creates pressure in the crankcase. This pressure must be vented or it will force it's way out of the crankcase and usually take oil with it - leaking gaskets and seals. Years ago, they would simply run a big tube from the side of the crankcase down under the car. Frequently they also ventilated the oil fill cap (the original 'breather') to vent the top of the engine as well. EPA decided they didn't want all that oil and hydrocarbon laden mess entering the air, and they required the valve cover to be vented into the air cleaner. After that, manufacturers began connecting the crankcase to the intake manifold via the pcv valve. Since the manifold 'sucks' on the crankcase, there has to be a path for air to get into the crankcase so you don't pull a vacuum on the crankcase - breathers use to do that too (let air in). But with efi cars, there's usually a connection between the throttle body and the valve cover (like our 5.0s) to let metered air enter the crankcase where it's returned to the intake via the pcv. That did away with breathers.

I'd think you'd have a hard time getting one past the emission inspection in CA.

 

[OonDeanisS]

so why then does my valve cover to throttle body hose let oil into my TB and intake if the air is supposed to be going from the TB into the VC? It looks like my intake is sucking vacuum on my valve cover and pulling oil up into the throttle body, so my entire intake and EGR system is coated in sludge.

 

[RacEoHolic330]

^That's not from your TB hose, it's the oil bypassing your PCV valve and making it's way into the intake. Check your PCV screen and the valve itself. Also make sure your lower intake is baffled. A very thin film of oil in the lower intake is relatively normal.

To the OP, most people use valve cover breathers if they decide to remove the PCV system (pointless in a N/A application) or if they go forced induction. At that point, most will typically install a remote catch can with a breather on that. Valve cover breathers tend to blow oil mist all over the place.

 

[OonDeanisS]

no, its clearly coming from my TB hose coming from the passenger side valve cover. When i look into the TB, i can see the oil build up coming from that port, and it has basically covered the entire upper intake and TB in black gunk.

Unless you're saying its coming up from the PCV and making its way into the TB past the open blade and into the tube... then id say thats crazy. How could the oil go against the air current when the throttle is open?

 

[Rick 91GT]

Original Poster- if you have a stock EFI system youll want to keep the pcv set-up and the original stock closed cap and line coming from the Valve Cover to the TB.

OooDeanisS-If you have oil in the TB it is DEFINITLY coming from the valve cover connection...or if you have a K&N filter it could be oil from it.

 

[OonDeanisS]

yea, its not the air filter, its thick black sludgy dry oil caked on everything from that port on the TB down into the intake. definitely coming from the valve cover hose. So... should i replace the cap or is that normal? i could get an oil separator but ive only seen them used on the PCV hose. As of now, i capped the TB hose and replaced the PCV valve and grommet, along with the crankcase filter.

 

[Rick 91GT]

What intake?

 

[RacEoHolic330]

Do you have aftermarket valve covers by chance?

 

[OonDeanisS]

gt-40 intake, and yea, but it still has that plate under the fill hole...

 

[OonDeanisS]

heres a pic...