question about p.c.v. hose

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Feb 12, 2009 | 02:25 PM

jbhofc

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question about p.c.v. hose

Since my 93 5.0 has blowby, can I just run the p.v.c. hose down the engine compartment somewhere? and cap off the vacuum Tee is hooks to?
I can't think that blowby is good to introduce into my intake.
I switched it from the back of the plenum to the middle of the plenum....now I'm thinkin' about just lettin' the hose hang down by the frame.
I am currently using heater core hose, is that strong enough to NOT collapse under vacuum? I was concerned about it getting warm and getting a little more soft and possibly collapsing.
That was the "thickest" walled hose that autozone had...should I look or ask for anything else?
Thanks, Mark

Feb 12, 2009 | 02:37 PM

Freightrain

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From: Ohio

I'd continue to run it into the engine and let it burn it. That was the basic operation of that set up. You can let it just vent to the outside, but you'll just have a mess where ever the hose stops. Back in the early days(pre 60s) that was called a Road Draft Tube, as it hung down into the air stream of the vehicle and let an induced vacuum pull the air from the engine. It led to a real mess under the vehicle as all the oil/moisture sprayed all over the bottom of the vehicle.

Std 3/8" rubber reinforced line is fine to use.

Feb 12, 2009 | 02:40 PM

Specialty Machining

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Blowby

Automotive engines have been burning blowby since the 1960's. There is a filter (probably in the air cleaner box to catch the crud) which usually needs changed before the air filter. If you have excessive blowby, then it's probably time to schedule some work. If you have to have emissions checked they may flag discharging to atmosphere. I wouldn't think you would have a physical problem in doing it since the PCV valve is just a check valve which only allow gases to flow out of the rocker cover.
Rod

Feb 13, 2009 | 08:46 AM

jas88

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Make sure you have vacuum at your pcv. I have had the vacuum port off the upper intake plenum, where the PCV hose hooks up, plug up with carbon on 2 302s. This made the air box get full of oil. After I unplugged it with a drill bit, things went back to normal.

If your pcv valve has vacuum, and you want to make a "road tube" (this is what you are proposing) don't run it off your pcv, hook it up to your crankcase vent tube that currently runs over to the air box.

Feb 13, 2009 | 09:58 AM

jbhofc

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Jas88.
Thanks for the pointer. I have capped the stub at the back of the plenum where the pcv valve hose originally went. (was told that was a major screw up in the 93 5.0's and caused problems in #8 cylinder.) Is that where you were talking about getting carboned up??? I have run it to the middle of the intake since there was an extra vacuum stub not being used. This stub had strong vacuum when I took off the rubber cap.
I think I am good with the vacuum.
I think I am confused, however. Does the tube coming from the air breather box take IN fresh air from the box?? OR is it supposed to be expelling extra crankcase pressure out into the filter? In other words, should air be going INTO the engine at the air box or be blowing OUT of the engine at the air box.?
I assume the filter was for filtering air being taken INTO the valve cover--hence, I am concerned about the puffing out of the tube.
Boy, I think I am confusing myself.........not too hard though. Ha Ha
Thanks for any help Mark

Feb 13, 2009 | 12:58 PM

jas88

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Yes, the PCV is applying vacuum to the crankcase, so the breather is to let filtered air in. If the blowby is such that it is overpowering the PCV (assuming it is working) then it will push air back into the air box which will then start to collect the oil in the vapors and it will eventually drip out.

Thinking about this a bit more, I think I told you wrong. If you are going to make a road tube, go ahead and attach it where the PCV was and run it under the truck with the outlet facing rearward. This will create a venturi effect as you are going down the road and draw the gasses out. In this setup, you will need an inlet filter to let air in, so your exising breather can serve that purpose. You would also need to delete the PCV valve and plug the vacuum port in this arrangement.