DINNUT- This is for you: PCV tech

[Tx Firefighter]

Take a few minutes to read to article below. You seems eager to learn, well here you go. This explains the basics of PCV systems. Half the working mechanics out there don't even have a grasp of this stuff.

Seriously, read it and think about it. This type of knowledge is what seperates the men from the boys.

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Positive Crankcase Ventilation (PCV)
Positive Crankcase Ventilation is a system that was developed to remove harmful vapors from the engine and to prevent those vapors from being expelled into the atmosphere. The PCV system does this by using manifold vacuum to draw vapors from the crankcase into the intake manifold. Vapor is then carried with the fuel/air mixture into the combustion chambers where it is burned. The flow or circulation within the system is controlled by the PCV Valve. The PCV Valve is effective as both a crankcase ventilation system and as a pollution control device.

PCV systems have been standard equipment on all new cars since the early sixties. Prior to 1963 PCV was only used in California. There are a variety of PCV systems used on various makes and models of cars produced since 1963, but all function essentially the same.

PCV systems can be described as either open or closed. The two systems are quite similar. However, the closed system in use since 1968 is more effective at air pollution control. The systems differ in the manner in which fresh air enters the crankcase and excessive vapor is expelled.

Open PCV Systems

The open system draws fresh air though a vented oil filler cap. This presents no problem as long as the vapor volume is minimal. However, when the crankcase vapor becomes excessive it is forced back through the vented oil filler cap and into the open atmosphere.<this is why tired engines get sloppy oil residue around the valve cover breather : Tx Firefighter> The open PCV system, though successful at removing contaminated vapors from the crankcase, is not completely effective as a pollution control device.

Closed PCV Systems

The closed PCV system draws fresh air from the air filter housing. The oil filler cap in this system is NOT vented. Consequently, excess vapor will be carried back to the air filter housing and from there into the intake manifold. The closed system prevents vapor, whether normal or excessive, from reaching the open atmosphere. The closed system is very effective as an air pollution control device.

The PCV Valve

The most critical part in the PCV system is the flow control valve, commonly referred to as the PCV valve. The purpose of the PCV valve is to meter the flow of the vapor from the crankcase to the intake manifold. This is necessary in order to provide proper ventilation for the crankcase, while not upsetting the fuel/air mixture for combustion.

Blow-by gases and vapor should be removed at about the same rate they enter the crankcase. Since blow-by is minimal at idle and increases during high speed operation, the PCV valve must control the flow of vapor accordingly. The PCV valve is designed to compensate for the engine ventilation needs at varying engine speeds. It is operated by manifold vacuum which increases or decreases as engine speeds change.

For example, at low or idle engine speeds manifold vacuum is high. This pulls the plunger to the extreme forward position, or manifold end of the valve. Due to the shape of the plunger, vapor flow is reduced to a minimum. The low rate of the flow is adequate for ventilation purposes and will not upset the fuel/air mixture ratio.



At high speeds manifold vacuum is decreased. The plunger is only drawn to a point about midway in the housing. This allows a maximum flow of vapor. Since the engine needs more fuel/air mixture at high speeds, the introduction of more vapor does not affect performance. In the event of a backfire, pressure from the intake manifold forces the plunger to the closed or engine-off position. This prevents the backfire flame from reaching the crankcase and exploding the combustible vapor.



A neglected PCV system will soon fail to function and the result can be expensive as well as troublesome for the car owner. If the crankcase is not adequately ventilated, the motor oil will quickly become contaminated and heavy sludge accumulations will begin to form. Internal parts, not protected by the motor oil, will begin to rust and/or corrode due to the water and acids that will become trapped within the crankcase. If the PCV system is not functioning properly, the flow of crankcase vapor into the intake manifold will not be properly metered. This, in turn, will upset the fuel/air mixture for combustion and cause rough idling or even stalling of the engine. Furthermore, intake and exhaust valves, in addition to spark plugs, may well be burned and rendered useless, prematurely affecting performance and requiring expensive repairs. To assure trouble-free performance of the PCV system and, in turn, the engine and vehicle, routine maintenance of the PCV system is absolutely recommended and required.

A PCV valve should never be cleaned and placed back into service. Cleaning a PCV valve will result in a clean PCV valve; not a new PCV valve. There are contaminants that will remain in the PCV valve that can never be flushed out. Additionally, there is an amount of wear that will be experienced by the spring that cleaning cannot replace. The recommended replacement intervals are a maximum of 12 months or 10,000 miles (16,000 km). Since vehicles and operating conditions vary, the valve may have to be serviced more frequently. If it is suspected that the valve is sticking or if there is evidence of sludge, the valve should be replaced.

All hoses or tubes used in the PCV system should be cleaned and inspected. If any cracks or breaks are noticed in the hose, it should also be replaced. All hose connections should be inspected to assure an air-tight seal.

Proper servicing of the PCV valve system will help reduce overall vehicle emissions.

[Longhorn Man]

Half the working mechanics out there don't even have a grasp of this stuff.

This is true. I had to explain this to one of our "master" techs at work.

[jorgensensc]

That's the 2nd article I've read on PCV valves. Very interesting.
Maybe I can put that on my Resume.... PCV Valve Expert. LOL

[Rooster's 67]

TX Firefighter, You are so correct in the knowledge of mechanics.

But then there is a difference between a mechanic and a Technician.

This type of knowledge is the difference

[greasemonkey]

Awesome article, it looks like the one in my service manual.

[Spoof]

I always thought vacuum increased at high speeds, not the opposite as indicated in the article. Perplexing
I wonder if the problems associated with a non-functional PVC are present on a non-PVC engine, of which I have seen many. If so perhaps they are overstated, if not I will definitly install PCV on my engine.

[oldsub86]

That is apparently why there have been problems with late model Toyota engines sludging up. It has been suggested that Toyota reduced the size of the PCV system in order to improve the environmental scores. Now the engines don't rid themselves of the bad stuff and they sludge up if you don't keep the oil real clean. May be time to put a new PCV valve in my wife's Avalon.

['68 K-10]

In some older vehicles before the pcv system they used a tube that released the oil and gases directly into the atmosphere. this was before pollution was a big problem. besides the heavy pollution that caused it also covered the bottom of the vehicle with oil and the road if it was a wore out engine with lots of blow-by just something i learned thought i would share

[dinnut]

my truck has the closed system which goes through the air filter and vented oil cap........ is that bad???? should i change the cap out?

wow i just learned alot!

[my new 72]

I am getting rid of mine and just runnung a vent cap on both sides. That answered my question as to whether it was a necessary piece of crap or not. My engine only has 5000 on it, so it does not pollute like it has 50,000.

[Tx Firefighter]

Originally posted by my new 72
I am getting rid of mine and just runnung a vent cap on both sides. That answered my question as to whether it was a necessary piece of crap or not. My engine only has 5000 on it, so it does not pollute like it has 50,000.

Are you serious?

Read the tech article above again. A PCV valve is a good thing! Why do you think engines back in the day were wore out at 75k miles and we see 250K plus miles out of engines nowdays? Things like PCV valves, that's why. They aren't just tree hugging environmentally friendly stuff, they are good for your engine.

Ever noticed that racers run crankcase ventilation systems on their race engines? It's not because they just want to. They understand the advantages to them.

[Stocker]

Originally posted by Spoof
I always thought vacuum increased at high speeds, not the opposite as indicated in the article. Perplexing

Engine vacuum decreases as engine load increases, and is at maximum when coasting (ie, throttle butterflies closed).

I am old enough to remember vacuum operated windshield wipers. Going uphill or passing (or any time your right foot was heavy), the wipers stopped working. Back off the loud pedal and they started working again.

[cableguy0]

DO NOT run your motor without a pcv believe me you will ruin the motor. it WILL sludge up bad whether its old or new it doesnt matter. the pcv is not just some emissions crap. it actually helps the engine stay healthy you need it.if you take it out now i will be waiting for your post in another 5000 miles about how your motor got all sludged up and took out a cam and some bearings good luck

[Tx Firefighter]

Also, back during the gas crunch, folks put vacuum guages on their cars and mounted them inside on the dash. Same deal, they tried to operate the engine at the highest vacuum level at all times for increased mileage.

Highest vacuum is carb closed and best mileage.

[BLACK AND BLUE 67-72]

Maybe this will help Spoof, http://www.mste.uiuc.edu/davea/aviat...Principle.html

It's the part under the venturi tube.

[my new 72]

I didn't say that I was going to cap it and not let it vent. I said I was goint to ditch the PCV and vent it straight out through a filtered breather. Read everything clearly before you reply please. I understand the concern, but the only thing it is doing is recycling the gasses into the carb and reburning them. If I vent it into the atmosphere what is the harm to the engine? It is still vented, just not recycled.

[dinnut]

thats what they are saying. dont vent it just leave the pcv. see air goes in through their and burns the crap off through the engine and with a vent it will just do not much and make yoru engine all dirty

[BLACK AND BLUE 67-72]

UUMMM, he wasn't saying that you were going to cap it, only saying that it is "BETTER" to run the PCV instead of venting it out, it is better to reburn the gases to help prevent the build-up of sludge and make your motor last longer!!!

[my new 72]

How does reburning the gases prevent buildup of sludge and help clean the engine? The article says that if the gases are not vented then the engine builds up moisture and other gases internally and causes the sludge and breakdown of the engine. The only reason it is vented through the PCV system is to recycle the gases and reduce emissions. Show me where it says anywhere that the PCV system does anything other than recycle gases that would otherwise be vented into the atmosphere and reduce emissions.

[BLACK AND BLUE 67-72]

my new 72, try reading paragraphs 6,7,8,9,10,and11. I think it is self explanitory pay close attention to paragraph #7 about the gases being removed at the same rate they enter! A straight breather will not increase the vacuum as engine speeds change hence the vacuum from the carb.

[BtnkBndt]

Great article TX!

I would also suggest you don't ditch the pcv. Without it you would loose the flow through the engine. The gasses would just kind of hang out in there.

Think of an old attic fan in a house. Open the windows and the house is vented. Turn on the attic fan and a flow is created that moves the air though the house, much better. Especially if your trying to air out the house which is what you want in your engine. My 283 is designed to be vented front to rear, later they are side to side through the covers. I am ditching the later model Edelbrock manifold on mine for an earlier offy with the oil filler up front so I can use sealed covers. I will not put the new covers on until I change manifolds, don't want a stagnant (sp) engine.

PCV=gooood

[BLACK AND BLUE 67-72]

BtnkBndt, excellent comparison^^^^!!!!