Venting PCV and Oil contamination.

[Bigsyke]

I was wondering if anybody had yet done any UOAs on a car with a PCV system venting to atmosphere? I have an NA 240sx currently, however running the catch can seems to make more of a restriction than going stock. The only downside to stock is I have to change the PCV valves almost every oil change, which requires about 4-5 hours of time.

Does synthetic such as amsoil provide enough protection against these blow by fuel vapors? There is alot of talk about how bad it is, but nobody has ever provided any proof.

Thanks in advance!

 

[StevieC]

You have to replace the PCV each oil change? You have big problems if that is the case...

Now to answer the question. UOA's seem to be much better where the PCV is vented to the atmosphere instead of through the intake but this is not legal in most places. Check with your local laws before doing this as you could get a nasty fine I know we can up here in Canada.

 

[chevrofreak]

You don't want it venting to atmosphere. You need vacuum to get all of the nasty stuff out, or you're likely to get sludge formations.

 

[StevieC]

Originally Posted By: chevrofreak
You don't want it venting to atmosphere. You need vacuum to get all of the nasty stuff out, or you're likely to get sludge formations.



That's not true.. My Austin mini vented to the atmosphere with no vacuum and it was 1960's technology and there was no sludging.

I know of some people

that vent to the atmosphere on their Toyota Sludgers and run 5K mile (8K KM) OCI's without issue on dino oil now.

(Just from what I have seen... If you have an experience of otherwise I would like to know.)

 

[Bigsyke]

Really much better? I thought they wouldve been WAY worse, id like to see some UOA's.

The ka24de pumps alot of pressure out of the crankcase-IM, which even in the FSM says most of the air will exit on the valvecover-intake. The PCV valve moves almost no air to even seem like it could put a negative pressure inside the crankcase even at idle when the IM is @ 21hg/in

 

[FastSUV]

Originally Posted By: chevrofreak
You don't want it venting to atmosphere. You need vacuum to get all of the nasty stuff out, or you're likely to get sludge formations.



what if you have a fuel injected V8 and one valve cover has the replaceable PCV valve vented into intake manifold, and the other valve cover has a "fixed" tube thing that is routed to the air intake tube...?

Would there be any harm/benefit to at least removing the tube that is the non-PCV valve fixed tube and replacing it with a mini air-vent filter thingy like you see on hot rods & souped up carbed motors?

 

[StevieC]

You don't need vacuum to pull it out, you just need to have a big enough outlet to allow it to breath it out fast enough.

On commercial buses they vent it to the atmosphere and not back into the engine on the older designs. (Uncle is a Bus/Street car mechanic for TTC in Toronto)

 

[chevrofreak]

Originally Posted By: FastSUV
Originally Posted By: chevrofreak
You don't want it venting to atmosphere. You need vacuum to get all of the nasty stuff out, or you're likely to get sludge formations.



what if you have a fuel injected V8 and one valve cover has the replaceable PCV valve vented into intake manifold, and the other valve cover has a "fixed" tube thing that is routed to the air intake tube...?

Would there be any harm/benefit to at least removing the tube that is the non-PCV valve fixed tube and replacing it with a mini air-vent filter thingy like you see on hot rods & souped up carbed motors?


The tube/hose running to the air intake tube is just to supply clean air to the system so that no dust/dirt enters the crankcase.

 

[robshelton]

Running for any length of time without a PCV is asking too much of any oil. Almost all contaminants and combustion by-products will stay in the oil. PCV - Positive Crankcase Ventilation - the engine normally operates under a vacuum to pull the junk out of the crankcase. If your Nissan has so much blow-by you need to change the valve at each oil change you might want to try some RESTORE or similar product, and/or try to change your driving habits if you are staying at higher RPM's.

I clean my PCV valve at every other oil change and still have the factory original at 347,000 miles. I don't know where your valve is, but I'd consider locating the vacuum hose that goes to it and spraying a healthy shot of brake cleaner or carb cleaner in it fairly often. This will help the valve replacement intervals, but be sure to keep your oil changed as there will be some cleaner that gets into the oil.

Good Luck!

 

[StevieC]

If you want to "Do away with" your PCV, it is important to do it properly.

Here are a couple of things you need to do in order not to upset the balance to your computer expecting that "metered" air leak.

1)The PCV that goes from the valve-cover to the Throttle body, usually goes after the MAF. So it is important that when you pull off the PCV you take that spot on the throttle body and pipe it into your air box so that it can still pull "un-metered" but filtered air. This will keep your idle in check and keep the Check Engine light off.

2)Take the PCV and attach it to a breather filter, locate it near the bottom of the engine near the firewall so that it is venting this underneath the vehicle. Do not use metal piping as this can freeze in the winter. Use Neoprene hose.

3)Unplug the breather line from the second valve cover or crank case (different on some vehicles) and plug up the hole in the throttle body where it goes, and vent this to the ground as well similar to described in step #2. Do not use a "T" to add both hoses together to vent to the same filter as this could create a problem on some vehicles.

 

[Bigsyke]

StevieC, ive been researching my PCV setup for about 5 years so far. There is about 100 million threads on different forums about this. I appreciate your input. Ive spent enough money tweaking my closed pcv setup that I couldve bought a new engine by now.

Yes most High HP hondas have an endyn kit that VTA. Ive always wondered how there could be negative pressure with such a huge restriction as the PCV valve.

Personally I see it as emmissions, and using the PCV valve is the only way to have it work in a closed system, wihtout a major vacuum leak. It seems that its really positive pressure forcing the vapors out, and the manifold vacuum catches them once the are FORCED passed the PCV valve.

The vacuum is only on decel and idle, where there is no vapors.

 

[StevieC]

Originally Posted By: robshelton
Running for any length of time without a PCV is asking too much of any oil. Almost all contaminants and combustion by-products will stay in the oil. PCV - Positive Crankcase Ventilation - the engine normally operates under a vacuum to pull the junk out of the crankcase. If your Nissan has so much blow-by you need to change the valve at each oil change you might want to try some RESTORE or similar product, and/or try to change your driving habits if you are staying at higher RPM's.

I clean my PCV valve at every other oil change and still have the factory original at 347,000 miles. I don't know where your valve is, but I'd consider locating the vacuum hose that goes to it and spraying a healthy shot of brake cleaner or carb cleaner in it fairly often. This will help the valve replacement intervals, but be sure to keep your oil changed as there will be some cleaner that gets into the oil.

Good Luck!


The only reason they are using vacuum is because they want it to flow into the air intake and not air into the crank case at idle/deceleration. When you "do away" with this system you don't need vacuum for proper venting. It's just important that the pressure is relieved and fresh air allowed to enter the crank case as needed. This will happen just by venting it to the atmosphere using my steps above.

I have this running on

and it produces UOA's with much better TAN readings over the same miles.

 

[chevrofreak]

Originally Posted By: Bigsyke
The vacuum is only on decel and idle, where there is no vapors.


There's still plenty of vapor. When I remove my oil cap to pour fresh oil into my engine when doing an oil change, there is a mist that is visible floating around in the valve cover. That's usually at least 15 minutes after the engine has been turned off. Imagine what it looks like when running.

 

[StevieC]

Originally Posted By: chevrofreak
Originally Posted By: Bigsyke
The vacuum is only on decel and idle, where there is no vapors.


There's still plenty of vapor. When I remove my oil cap to pour fresh oil into my engine when doing an oil change, there is a mist that is visible floating around in the valve cover. That's usually at least 15 minutes after the engine has been turned off. Imagine what it looks like when running.
I have seen the same with/without PCV systems on cars. It's inevitable. At least with one vented to the outside it can vent after shut down. In a PCV system it can only float around a hot engine with nowhere to go.

 

[Gary Allan]

Quote:
The vacuum is only on decel and idle, where there is no vapors.


Under high manifold vacuum, the PCV valve is a regulated and filtered manifold leak. Under higher rpm, it's like a parallel intake ..within the limits of the hose and the restriction of the valve itself.

Mount bigger hoses (adapt - BIG HOSE - adapt back). That should slow down anything heavy without the restriction of the catch can.

If you want to cheat, yet be socialized about it, get an extractor from Jegs and install it in the exhaust. Don't bottle it up or you may suck in a seal. That is, leave the fresh air inlet intact.

 

[Bigsyke]

Garry

Most autos with mufflers according to some people on Honda-Tech have reported positive or almost no negative pressure on the slash cut.

Most engine have leaky seals, thus no matter what you read on the web, you will never achieve negative vacuum in the crankcase, have you tried sucking on those valves? not gonna happen, plus when the opposing side of the PCV system is a 5/8ths tube with no restriction.

The vapors are forced out, where the vacuum then pulls it once it gets forced past the valve


On the nissans KA24de, if you cap the IM side, and the TB side you will have no changes to the MAF reading. The IACV makes up for the idle according to the base idle

 

[d00df00d]

I agree that if you are having to change your PCV valve every oil change, something is wrong.

As far as I know, the only oil right now that is specifically said to prevent fuel from getting into the oil better than others is RLI BioSyn.

What oil are you using now? If it's dino, you would definitely get some benefit out of switching to almost any good synthetic just because of the lower volatility. Get the lightest viscosity your engine can take to minimize air entrainment.

 

[Bigsyke]

Ive been using amsoil 5w30.

The car is slightly modified however;

No evap canister- vented
No EGR system
Modified cooling system *149*f nismo Tstat

The PCV valve on the nissan gums up real quick, the hose angles upwards, thus the oil vapors end to collect at the valve with shorter trips or cold weather. The PCV valve hose splits 4 ways to 1/4 hoses connecting to each of the IM runners.

The system is horrible. The hoses crack, the valve is tucked behind the alternator and you have to remove half the engine components to even see it.

 

[d00df00d]

Do I understand correctly from your first post that you are having some fuel dilution issues?

 

[Bigsyke]

I was wondering if VTA will cause fuel dilution issues, I had issues with a nismo FPR and an incorrectly adjusted TPS.