There is a PCV valve & hose on the top of my engine venting gases back into the intake. But I noticed there is another hose on the side of the engine valve cover connected directly to the intake with no PCV valve in-between. Why? What is it for?
Engine Venting
- Thread starter Ken4
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Looking at where the hoses are attached to the intake system will help answer the question.
The hose with the PCV valve is downstream of the throttle body so it has relatively high manifold vacuum in it. The blow-by gasses, water vapor, etc. are drawn from the crankcase into the intake system through this line and metered by the PCV valve.
The other hose is between the throttle body and the air filter, so this hose has clean, filtered air at just slightly below atmospheric pressure in it. This hose supplies clean make-up air for the crankcase. If you didn't have this hose, the crankcase would end-up having almost the full vacuum of the intake system in it. This would be bad because the oil pan gasket, valve cover gaskets, oil seals, etc. are not designed to hold a relatively high vacuum like that.
The other hose also has a second function. When the engine is at full open throttle, the intake manifold vacuum drops to very low levels. Under these conditions, the flow through the PCV valve can stop. In this situation, the flow through the second hose reverses and the blow-by gasses, water vapor, etc. exit the crankcase via the second hose and are routed into the intake system.
[ February 05, 2003, 11:25 PM: Message edited by: Rick in PA ]
The hose with the PCV valve is downstream of the throttle body so it has relatively high manifold vacuum in it. The blow-by gasses, water vapor, etc. are drawn from the crankcase into the intake system through this line and metered by the PCV valve.
The other hose is between the throttle body and the air filter, so this hose has clean, filtered air at just slightly below atmospheric pressure in it. This hose supplies clean make-up air for the crankcase. If you didn't have this hose, the crankcase would end-up having almost the full vacuum of the intake system in it. This would be bad because the oil pan gasket, valve cover gaskets, oil seals, etc. are not designed to hold a relatively high vacuum like that.
The other hose also has a second function. When the engine is at full open throttle, the intake manifold vacuum drops to very low levels. Under these conditions, the flow through the PCV valve can stop. In this situation, the flow through the second hose reverses and the blow-by gasses, water vapor, etc. exit the crankcase via the second hose and are routed into the intake system.
[ February 05, 2003, 11:25 PM: Message edited by: Rick in PA ]
That's the breather hose, which completes the PCV loop. This takes blowby gasses and puts them into your intake to be burnt off by going through the engine.
Without a well-functioning positive crankcase ventilation system, your oil would get dirty very quickly!
Without a well-functioning positive crankcase ventilation system, your oil would get dirty very quickly!
Shouldn't this be "slightly above atmospheric pressure" from the mild ram-charging effect occuring in the intake plumbing? After all, this venting system is called "positive crankcase ventilation" for a reason. By positively charging the engine's innards, any combusion vapors are then purged throught the one-way PCV valve.
What Rick said. The others are confused. The movement of the air is away from the intake tube which is where the PVC system gets its makeup air. Incidently this is how your oil gets Silicon in it if you use a "low restriction" air filter element or allow the one thats in there to get overwhelmed. The contaminated air is drawn from the valve cover by engine vacuum to be burned with the mixture. "ram charge" is only a very temporary phenomina that occurs at the valve when the valve closed and the air continues to flow briefly until the valve sees slightly greater than ambient pressure when the valve opens again. It happens only at certain RPMs and is local to the valve seat.
I don't know about other cars, but I find it hard to believe that there's any ram-charging effect that survives the convoluted trip through my car's intake, resonator, and air filter. The hole that air enters the system through isn't even pointed forward.
All that's required is that the pressure be positive compared to manifold pressure.
Oh sorry, forgot to mention that the direction the gasses flow in the breather hose is from right to left
quote:
Originally posted by Ken4:
So which way are the gases moving?
According to Mike, who I think is on top of the situation, the flow is right to left, except when it is left to right (wide open throttle, high load). However if this happens much the engine is probably on its way to the bone yard. Some engines that draw from the outside of the air filter element will quikly oil foul the filter paper if there is too much blow by.
Thanks... I'm getting really good at googlequote:
Originally posted by Ken4:
Thanks S2000! That article is very good.
Hi Ken.
Here's a link for you: http://www.autoshop101.com/forms/h63.pdf
I'm not confused... don't really like being insulted either.
Paul
Here's a link for you: http://www.autoshop101.com/forms/h63.pdf
I'm not confused... don't really like being insulted either.
Paul
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