There's a reason it's called Positive Crankcase Ventilation...

 

If everything is working well, there should be absolutely minimal amount of oil vapor coming from the PCV system.

However, in the real world, there is some blow-by in the PCV system. A catch can will stop most of this from being drawn into the intake by allowing the oil vapors to cool and condense in the can, and allow the air drawn by the PCV system to continue without it.

This is NOT a source of lubrication for the engine, it is there to provide a "clean" exit for blowby gasses. The oil vapors exiting the crankcase this way are merely a side-efect.

Unfortunately, since the intake air tends to be much cooler than the crankcase air, the usual result of oil vapors from the crankcase entering hte intake stream is that the oil vapors condense into oil, which makes a mess in the intake. A catch can should reduce this.

 

Well if the catch-can is fitted in series between the cam-cover and the throttle body and it stops the oil, thats got to be a good thing. If that recirculating oil is not needed why didn't toyota fit a catch-can there at the factory? After all its only contaminating the air in to the engine with oil. Strange.. Thanks for the response.

 

because the catch can isn't legal.

 

If the catch-can was venting to atmosphere then I can see that that would not be legal. but if all your doing is trapping the oil before it gets back to the throttle body then there is no change in emissions, if anything the emissions may be lower as you are no longer burning that oil off. Or am I missing something here?

 

Well, originally, the vapor was just vented to atmostphere, or allowed to condense and drip on / into the exhaust and burn off there.

Then we introduced emmissions laws, which did not make auto manufacturers very happy.

"Fine," they said, "we'll take care of that oil vapor by making your engine burn it."

"Wait a minute," we said. "That's not very good for combustion!"

"True. But you can't have your cake and eat it too. If you want to prevent us from venting it to atmosphere, you're going to have to burn it."

"What about installing a catch can?"

"Too expensive. It would cost us millions of dollars to put those in every vehicle we make. And don't even think of trying to legislate catch cans into every vehicle made, because I bought 63 politicians in the white house this year, and I don't care how many helpful food regulations and child porn laws you sneak in with your catch can bill, I'll have my politicians shoot it down. So take that, you green bellied tree hugging eco terrorist."

I'm sure my replay here isn't entirely accurate, but the gist of it is there, and my version is funny.

 

I'm missing something here... That PCV pipe that gets tossed feeds the TB two different ways, one by the small tube right on the TB and the other by recirculating through the accordion hose... I was thinking of installing a catch can (home made or a fancy pants one) but how is all this (catch can) really hooked up, is it in series between the PCV tubes and ??? what, the tube on the TB or the accordion hose? If on the accordion hose, do you block off the small tube on the TB? Also, what about the two vacumm hoses on the top of the TB that seem to be related to this PCV tube on the TB. When I rebuilt the head, I cleaned up the TB and there was a lot of gunk inside this tube and stuff came out these vacumm ports. I have not found a good diagram of what gets plugged, what gets routed and what just does nothing.... I do agree that the catch can is a must as, man, there was a lot of gunk in the tubes and TB from the PCV. Imagine what the intercooler does to the oil fumes as they get sucked in through the accordion hose / turbo...

 

those ends are capped off. u have 2 hoses running off of ur valve covers to this catch can with the filter on top of the catch can. the reason why people do this is to keep the oil out of the intercooler and pipes.

 

does running a catchcan in line between the PCV crankcase vents and the TB allow the oil vapors enough time to condense inside the can, or is it just making more distance for the oil to travel before making its way back into your intake to condense there?

 

There are 3 main reasons why the manufacturer did not install a PCV catch can.

1. Cost. It costs money to put more stuff in the car. While this may not be a huge expense in and of itself, it does add some. It is also one more thing which will almost certainly cause warranty claims. (The catch can is filling too quickly, my engine must be bad!) The primary cause being people running too long between oil changes. This leaves the manufacturer only two options: Refuse the claim, and get a reputation as having a lousy warranty, or pay the claim, and lose money. Either can be costly to a car company.
   
2. Need. While still under warranty, the amount of oil vapors going through the PCV system is unlikely to EVER cause a problem. As long as the rings are sealing properly, the amount of blowby into the crankcase, and thus the amount of crap getting sucked into the PCV system will be very small. With everything in new or nearly new condition, this should NEVER be a problem.
   
3. Maintenance. If there's a catch can under the hood, then that's one more thing depending on the owner to check, and possibly drain. A typical car owner is bad enough about checking the oil, adding in one more thing to an underhood checklist is not going to help matters.

The PCV system is only partly an emmissions issue, it's supposed to remove blow-by gasses from the crankcase, thus preventing them from escaping to the atmosphere, and also preventing them from forming corrosive acids in the engine oil. (The same acids that form in the coolant when you've got a BHG.)

 

There are some good points going here. I was thinking about making a catch-can out of aluminium, the cam-cover's pipe fitting about half way up the can and the feed to the tb from the top. With a bit of perforated ali between as a baffle. I was thinking of putting a drain off the bottom of the can and using an electrically operated popet valve to allow the collected oil to drain back to the sump only when the engine is switched off. I can make all this crap myself but was wondering if it would be benificial? I imagine that not putting oil through the tb would. Would it be ilegal?
Thanks for everyones input. Gary.

 

because the catch can isn't legal.

:wtf: Yes it is... Saabs have them from the factory.

 

Toyota sort of built a catch can into the cam cover design. Next time you have them off, check out the top part of the cover.

Its a bad idea to mess with the PCV system for several reasons.

1) The driving force for succesfully keeping the crankcase under a vacuum is very low. Adding a catch can into the path between the crank case and the throttle body increases these losses.

2) The engine management system actually accounts for some oil vapor coming into the intake. This is important because that oil vapor affects the overall octane of the air/fuel in the combustion chamber. (This is true of an EGR when not under boost as well)

3) Failure to maintain a vacuum on the crankcase causes pressure to build on the wrong side of the piston rings. This can affect horsepower and in extreme cases impact the rings ability to seat properly. This in turn increases blowby and makes original problem of too little crankcase vacuum worse.

4) Ironically, for the PCV system to work as designed, it also relies on the restriction of the OEM air filter. Under boost, that restriction insures that the "accordian tube" at the turbo inlet has vacuum to pull from the crankcase. But, eh, thats the first thing people mess with not realizing that they have affected the lifespan of the rings and increased the risk of leaky gaskets all over the engine.

 

Mr Turner makes some very lucid points.
1) True, but remains far superior to a breather can, which is what many have done.
2) Much of the condensate that I've had to clean was comprised of moisture, besides a small bit of oil. Whatever it is, most prefer having a clean intake tract/IC/TB/etc, while wondering whether the ECU is actually having to compensate is irrelevant to those who already manage fuel. I do.
3) True, & why vacuum pumps are often found on high HP domestics. I won't get into specifics, but more power is part of the deal.
4) True! Heh, Dean M ran 16psi boost thru stock air filter box & witnessed the accordian hose collapsing a bit. That was an interesting observation. Mike B on the SOGI list just measured his accordian hose vacuum w/high flow Apexi:
I did some zoming around today with my vacumme, HKS 60mm P&H, hooked up to the PS connection on the Accordian Hose. FYI I have a bone stock turbo, except for ceramic coating and and EGT sensor, the APEXi air filter and I am running at stock boost. At full throttle, 0.4 Bar, up to 4000RPM the most vacume I got was about 33mmHG. Ie is looked like it was about 1/3 but not a 1/2 or a 1/4. This matches with what I saw when I hooked up a vacume gauge to the oil filler cap awhile back. There is no huge vacume, but also no pressure.

Bottom line? Many mods incur trade-offs. Living with them, or not, is up to you.

Great counterpoint, Mr Turner

Take care.

 

Thanks everyone. I wont bother messing with this system, too many if's and buts! I will leave it as nature intended. Gary.

 

yea, I feeling the same... too many ifs.... There is no clear resolution as to if it is for the better or for the worse.... Maybe if it wasn't a daily drive, the results or benefits would be different. It is a great thread though... lots of knowledgeable info... praise to you gurus :hail:

 

Thanks for the balance Lorenzo.

I hadn't actually taken pressure readings at the compressor suction. Since most centrifugal pumps (air or otherwise) do not work well without some inlet pressure, it wouldn't suprise me if the suction in the accordian tube is almost negligible under boost. This is of course a much better option than manifold pressure, but this indicates our cars were not intended for extremely long periods of boost.

You know, I'd really prefer a dry sump with a crankcase vacuum pump, but I'm not sure anyone has ever done this on an MKIII.

 

I just installed two breather filters on my covers. Some people have said that they get oil residue on the covers and on their engine, but I have yet to see any oil. I did however love the fact that there was no more oil in my intake manifold. I had the manifold off, and hosed it out for about 10 min with STP throttle body cleaner, and finally got all the shit out. I gained a couple high end hp from it too.

Breathers where much cheaper and easier than a catch can, but you just got to put up with a little smell from the crankcase gases pouring out into the atmosphere. No biggy.

 

~with my powers of ressurection~

How much will the pressure be affected if the catch can is not venting to the atmosphere? Just have an inline fitler and can, but still routed into your intake. I can see if you let the filter in the can get to clogged it would limit vacuum, but... I was considering doing this, now Im not so sure. I do know I don't want any more oil collecting in my IC after I clean it all out.