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Old 09-28-2007, 10:19 PM
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Oil breather cap

What is the purpose of an oil breather cap? Can I get away with out one? the reason i ask is i am going to put a nice air cleaner on and the one i like doesn't have a hook up for my oil breather cap. so what can i do just plug it off or what can i route the hose to? Any advice is appreciated.
thanks

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Old 09-28-2007, 10:42 PM
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You have to have suction out of the engine and a fresh air return into the engine.
Normaly that would be a PCV valve in the front of the drivers side valve cover and the pipe(factory)from the air cleaner to the passenger side valve cover.....If thats what you are talking about,you can replace the pipe with a open air breather.
As far as "oil breather cap" the old motors had a road draft tube at the rear of the block that went to the underside of the car using the under car air turbulance to suck out the crank case fumes and the fresh air return was at the vented oil cap on the oil filler tube.
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Old 09-29-2007, 01:29 AM
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Yeah, you really should have one. The PCV system is pivotal to oil health and it can't work right without one.

It doesn't have to be in the valve cover, though. You could drill and put one next to the distributor, or use a hose from the valve cover to a breather that's hidden somewhere.

I drilled one in the back of a cast valve cover once to keep things neat.
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Old 09-29-2007, 06:03 AM
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Im not talking about the pcv valve i have one and it works fine im talking about the oil breather cap.
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Old 09-29-2007, 07:13 AM
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that will work fine. as long as it doesn't leak oil. putting one directly on the v/c very probably will leak some oil. raise it up off the v/c with a hose or something, and it should be fine.
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Old 09-29-2007, 07:22 AM
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Quote:
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!

Steve
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Old 09-29-2007, 10:53 AM
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Ok thank you sorry for the confusion i just needed more detail of what you where saying i understand now.
my oil breather cap is what i want to replace with a stand alone filter so i can run a better air cleaner. do you know of a place where i can find one?
thanks again
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Old 09-29-2007, 11:40 AM
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PCV breather

NAPA, Autozone, Pepboys, anyone of them and many others will have the chrome breathers.
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Old 09-29-2007, 03:30 PM
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Quote:
Originally Posted by viking

What is the purpose of an oil breather cap? Can I get away with out one? the reason i ask is i am going to put a nice air cleaner on and the one i like doesn't have a hook up for my oil breather cap. so what can i do just plug it off or what can i route the hose to?

Any advice is appreciated.
Your present system is referred to as a Closed PCV System, i.e. fresh air is filtered through the carburetor air cleaner before it enters the crankcase. Usually, aftermarket air cleaners have a knockout on the bottom plate to mount a breather asm still using the closed filler cap. Barring that, you need to obtain what is referred to as an Open PCV Sytem fill cap, i.e. there will be a filtering element in the filler cap itself and the fresh air tube is deleted.

Very basic...
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Old 09-29-2007, 05:55 PM
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the pic is where i unhooked my hose from my oil breather to my air cleaner and plugged in a oil breather filter unsure if this is how it should be installed if not please correct me
just so i understand what your talking about when you say a closed system since my oil fill cap is closed i need to run a oil breather cap other wise i need to find an oil fill cap that is breathable.
if i understand you correctly.
thanks
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Old 09-29-2007, 07:50 PM
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Oil breather cap

If you have room to just remove that whole assembly from the valve cover and plug the filter directly into the valve cover. If it fits snug , of course. If not find a breather that does.
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Old 09-29-2007, 10:11 PM
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Don't molest your oil filler or your PCV setup. Just get a good filter cap that fits the grommet in your valve cover. I got a K&N breather, cut off the bottom because it wouldn't fit into the grommet and siliconed a grommet to the bottom of the filter. It's been working for ten years, it looks good,and it's easy to remove and clean.
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Old 09-30-2007, 02:47 AM
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Quote:
Originally Posted by viking

the pic is where i unhooked my hose from my oil breather to my air cleaner and plugged in a oil breather filter unsure if this is how it should be installed if not please correct me
You have the correct basic idea and it is OK if you are not concerned about appearance.

Quote:
just so i understand what your talking about when you say a closed system since my oil fill cap is closed i need to run a oil breather cap other wise i need to find an oil fill cap that is breathable.

if i understand you correctly.
Correct. The easiest and cleanest way out is to find a suitable open oil filler cap (will have a filtering element in cap).

That cap is the fresh air ingest side of the PCV System. The crankcase needs a fresh air source to operate properly.
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Old 09-30-2007, 06:32 PM
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thanks for the info i fixed it with a different grommet
heres a pic of the new setup
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Old 10-01-2007, 07:48 PM
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Quote:
Originally Posted by 78 monte
You have to have suction out of the engine and a fresh air return into the engine.
Normaly that would be a PCV valve in the front of the drivers side valve cover and the pipe(factory)from the air cleaner to the passenger side valve cover.....If thats what you are talking about,you can replace the pipe with a open air breather.
As far as "oil breather cap" the old motors had a road draft tube at the rear of the block that went to the underside of the car using the under car air turbulance to suck out the crank case fumes and the fresh air return was at the vented oil cap on the oil filler tube.
The road draft tube on old motors did not work by "under car air turbulance to suck out the crank case fumes" It was the pressure within the engine that pushed the fumes out. The fumes escaped even when the vehicle was parked and the engine running. It was also the way water in the crankcase was allowed to evaporate out of the engine.
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