Tubing - Air box to Oil Filler Cap

[O'Rattlecan]

In my 1994 OBD I vehicle, I have a tube that goes from the oil filler cap to the air filter box on my pickup. It's the 351w, and I was just thinking...

Is this necessary? It seems to remove bad air from the crankcase and valve bodies. Isn't this what the PCV valve does? Is this a redundant system?

Ryan

 

[mrfixit]

You are correct, sir. It allows the intake to "breathe" crankcase air post-filter. I wouldn't just cap it off, tho. I did re-direct mine to just release into the atmosphere and my TPS never needed cleaning again...

 

[O'Rattlecan]

Awesome... I think I'll just let it breathe that way then.

Ryan

 

[Skandocious]

You might want to run it somewhere out of the engine compartment or it could start to develop a nasty oil spot in your engine compartment.

 

[O'Rattlecan]

I was thinking about dumping it downward so dirt is less likely to go up the tube but I can send the oil down into a nice spot on the driveway.

Ryan

 

[mrfixit]

well, straight down from that point is the crossmember, and they'll hold a lot of oil before it gets to the ground

 

[O'Rattlecan]

'rust prevention'

Ryan

 

[Blue Goose]

If you remove that from the airbox, you'll be sucking unfiltered air (read dust etc) into your engine crankcase.

 

[O'Rattlecan]

Well I was going to plug that one as well.

Ryan

 

[mrfixit]

Yeh, I just bought an expandable rubber plug- I believe it was 1 inch- and used that to close the hole.

 

[Skandocious]

Did we ever figure out just why in the world we've got the PCV (positive crankcase ventilation) and yet we still need to have this breather tube that makes a mess in my intake?

My truck is not like some of those where it goes to the airbox and has a fancy little filter. No sir-- direct from the factory the tube connects direct from the filler neck to the middle of my intake duct, about 12 inches from my throttle body I peered inside the other day when I was doing my sag pump swap and it was all slimy inside I'd sure like to cap it completely if it serves the same purpose as the PCV. Dumping it into the engine compartment somewhere is not an option for me.

 

[O'Rattlecan]

You've got me man. Maybe they don't want crankcase vapors in the valve covers as well??

Ryan

 

[Skandocious]

Okay Brad just called me to harass me about being stupid It's so obvious why it's there-- the PCV is what extracts fuel vapors from the crankcase, and in a sealed system you must DISPLACE those fuel vapors with new, fresh air. The line coming from the airbox allows twice-filter air (air filter + breather filter) to displace the fuel vapors that just left your crank case. DO NOT disconnect the breather line from your airbox or you'll start sucking UNFILTERED AIR through that hose and into your crankcase.

Clear as mud?

 

[O'Rattlecan]

That took a rocket surgeon to figure out. Whoops. Maybe I just need an air filter off a mower to put on the valve cover rather than replacing the whole stupid hose.

Ryan

 

[mrfixit]

I neglected to mention that I was kidding about just letting it hang down- I screwed a coffee can to the wheel well and strapped the hose into the can. Closed off the airbox so it's not sucking in dirty air with the aforementioned rubber plug.
Don't plug it up, though. As vapors build in the crankcase, not all of them are pulled off by the pcv. The opposite bank needs to breathe as well, or oil to the valves can be impeded by the slight backpressure.

 

[Skandocious]

I neglected to mention that I was kidding about just letting it hang down- I screwed a coffee can to the wheel well and strapped the hose into the can. Closed off the airbox so it's not sucking in dirty air with the aforementioned rubber plug.
Don't plug it up, though. As vapors build in the crankcase, not all of them are pulled off by the pcv. The opposite bank needs to breathe as well, or oil to the valves can be impeded by the slight backpressure.

Tom if you've got the hose routed to an empty coffee can then you're sucking unfiltered air into your valvecover... I'd suggest either reconnecting it to the airbox or somehow fitting a filter on the end of that hose.

 

[mrfixit]

Chris, on mine- and I don't have others to check, there is nothing but positive displacement from that hose.
When it is attached to the airbox, it is in a negative-pressure environment. Air is pulled thru that hose, with its vapors entering the intake stream. Standalone, it is putting out vapors, not sucking air in.

 

[Skandocious]

I'll have to read into it and get back to you on that Tom.

 

[mrfixit]

That's fine, Chris. I can understand.
But take a hard look at what it does- it is there to recycle blow-by into the intake so that vapors are burned off. That is why you had that oily scum you mentioned. It pulls blowby off of the right bank, and the pcv typically handles the left bank.

 

[89frankenford]

That's fine, Chris. I can understand.
But take a hard look at what it does- it is there to recycle blow-by into the intake so that vapors are burned off. That is why you had that oily scum you mentioned. It pulls blowby off of the right bank, and the pcv typically handles the left bank.

are you saying that both banks need a bailout?? lol



i know i know REALLY bad joke