Serviced, now a pressurised oilcap???

[Custard]

Hey, myself and Prawn, serviced my a3 1.8t today, consisting of oil and filter change, fuel filter and pollen filter.

we also noticed there was a massive split in the pipe that goes from the inlet manifold to the pcv check valve.

on prawns audi, his was also split, and we figured it was an emmisions based thing, so he cut the pipe and blocked it off going into the inlet valve. thus removing his boost leak. he didnt block off the pipe coming out the block. (as he couldnt be bothered)

we did the same on mine, but i didnt wanna leave the pipe open, so stuck a bolt in it.

when we turn the car on, it started and then cut out. started again and was ok.

when we get home (5 mile) i turn the car off, and went to top the oil up a bit, on undoing the oil cap it hissed, releasing pressure... im quite sure its never done that before! this isnt right surely ?

Any help appreciated.

Cheers Dave

 

[S3 Paul]

You have created crank case preasure i think.
The blocked off pipe must be part of the breather pipe. Meaning it must be free to blow the fumes from the crank case to the rest of the breather system (or the atmospher on prawns car)
I would remove the screw until you can correctly replace the full hose.

 

[A3Tom]

Yep, sounds like you've blocked a breather pipe for the crankcase or something.

As suggested either replace it or lob a little filter on it.

 

[Caesium]

I'd get that done asap or you'll blow a seal out.

 

[Custard]

yeah thats what we were thinking!, havent driven the car since, lets hope its ok, il take the screw out first thing tomorrow.

i think i wil leave it venting to atmosphere, with a filter on it, as surely having it breathing into the inlet manifold will be increasing inlet temps?

on that matter tho intrestingly we vagcom'd my car before this service, and the inlet temps were about 43*C so will have another look tommorrow and see if there any lower!

Thanks for the help guys!

Dave

 

[pauldazzle]

I'd get that done asap or you'll blow a seal out.

100% correct.
You probably haven't blown an oil seal yet as it's pressured up, but you soon will.

 

[NHN]

Yeah concur

 

[1animal1]

yup, high air pressure in the engine will cause oil to rise to places it doesnt normally go.... thus causing the said failure... matter of time really

 

[Prawn]

hello chaps. Daves car is mighty odd, but the pipe we blocked up definately wouldn't have this effect unless the rest of the PCV system was blocked.

The standard AGU pcv system, has one outlet on the block below the inlet, and one comming from the top of the rocker cover. these join together, and then a single pipe does into the 'hockey puk' valve on the TIP.

The split hose in question was the hose running from the underside of the inlet mani to the PCV check valve. it was split and causing dave to lose boost.

We plugged the pipe from the inlet mani, obviously fixing the boost leak, and Dave wanted to plug the hose from the PCV valve too, although it was pointless as it was split further near the valve anyway.

Anyway, the little 8mm hose we plugged was just the one comming from the PCV check valve to the inlet. the PCV system is still able to vent normally from both outlets back into the TIP, and the vacuum in the TIP will still draw gasses out to a degree. we havn't blocked off anything that's not blocked off under boost conditions (like the PCV check valve hose when the valve shuts).

The only way that this little pipe being blocked COULD have caused any crank case pressure, is if the lower PCV hose was blocked after the check valve, but before the split to the rocker cover take off, as we were able to blow cleanly from the rocker cover pipe direct to the hockey puk on the TIP.

Still, we took the plug out and it's fine, although obviously no pressue vents through this little pipe still anyway.

I personally think it was an unrelated fluke

 

[Broken Byzan]

100% correct.
You probably haven't blown an oil seal yet, but you soon will.

Couldn't resist

 

[Caesium]

Rings have gone then....

 

[Custard]

If the rings have gone, surely it would be burning alot of oil and have significantly reduced power?

It burns very little oil and pulls very well. It also has very good full service history, i know this means very little, but its not like its had a unlooked after thrashed life.

 

[Caesium]

Rings on way out doesn't necessarily mean loads of burning oil, its just piston blow-past ends up in the crankcase and builds up pressure.

Just a thought.

 

[auroan]

Am I the only one thinking "why re-engineer what Audi spent a lot of money designing and just put a new pipe on to replace the split one" ?

 

[Prawn]

Am I the only one thinking "why re-engineer what Audi spent a lot of money designing and just put a new pipe on to replace the split one" ?

No, I've already told Dave to expect posts of that exact nature.

the point is, the PCV check valve is a very common leak source, and it serves no real purpose, so you may as well do away with it. Rather than spend £20 on a replacement hose, and £5 on a new check valve, you can simplify an overly complex system for no cost at all.

 

[Prawn]

to further your question....

Why remap a car? Audi obviously gave it enough power
Why upgrade the brakes? Audi obviously gave it good enough ones.....
Why upgrade the stereo? it already plays music.


The list of similar situations goes on, but questioning them does not help solve the original question....

 

[auroan]

to further your question....

Why remap a car? Audi obviously gave it enough power
Why upgrade the brakes? Audi obviously gave it good enough ones.....
Why upgrade the stereo? it already plays music.


The list of similar situations goes on, but questioning them does not help solve the original question....

Hang on. The solution is to replace the pipe. Do you have enough experience/qualifications to warrent your damming of the breather system ?

Because your advice in removing the pipe and blocking the holes is causing the issue.

The solution as I see it is to put the correct parts back in place. Not try and redesign it.

 

[Custard]

I appreciate your replys Auroan, and you are 100% right replaceing everything with standard parts would have to run how audi intended, however audi designed it with everything working 100%, at 162k alot of the valves and pipes proberly arnt working as they should.

As i understand it this pcv check valve is only there to re-burn crank case gases, to improve emmisions produced by the car. Now as alot of people on this forum tune their cars for performance, recirculating hot gases back into the inlet manifold isnt a great idea. simple logic of tuning a engine.

I think my next job is to remove all the breather pipes and clean them as they are proberly gunked up. i also think it may be worth replaceing the "hockey puck" thing on the TIP as perhaps that is restricing flow.

Regards

 

[Kunit]

Unfortunately you are wrong and clearly don't understand the system, if I were you I'd leave well alone before permanant damage is caused. Crankcase gasses have to go to the inlet as they aren't allowed to vent to atmosphere and have nothing to do with emissions and are not recirculated also they really aren't going to make that much difference to intake temps.

 

[Prawn]

Do you have enough experience/qualifications to warrent your damming of the breather system ?

Because your advice in removing the pipe and blocking the holes is causing the issue.

.

I never told Dave to plug up the hole from the PCV valve, infact, I actively told him not to, as I didn't think it was needed, or helpful.

The simple fact is, the tiny 8mm hose from the check valve to the inlet CAN'T be important, because it closes under boost (by way of the check valve), which is surely when the engines needs to breath most? when it's being thrashed....
At this point the valve is closed and nothing can flow to the inlet. By blocking the pipe, you are effectively just replicating the system in it's 'on boost' capacity.

As i understand it this pcv check valve is only there to re-burn crank case gases, to improve emmisions produced by the car. , recirculating hot gases back into the inlet manifold isnt a great idea.

Regards

Stop going on about hot air the check valve closes under boost anyway, so nothing can get in when it matters.

Crankcase gasses have to go to the inlet as they aren't allowed to vent to atmosphere

Why do they HAVE to go to the inlet? they don't on many other cars. on my mini the breathers are all plumbed into a can of fosters!

Anyway, ultimately, it is all still going via the inlet, as the PCV is a sealed system between the TIP and the block/rocker cover outlet points, so the vacuum in the TIP will still be drawing the gasses out from both points.

 

[Caesium]

Where does the pcv escape to when the car is on boost? I never thought of that!

 

[Prawn]

it'll be drawn down the TIP wont it, as we all know TIP's are famous for collapsing when a car is remapped, this is beause the turbo sucking in so hard creates a fairly substantial vacuum inside the TIP.

The main large bore (19mm) PCV pipework connects to the TIP via the hocket puck valve, so I'd assume the PCV system is most effective on boost, exactly how we've rigged it to be on custards car

 

[pauldazzle]

Vacuum in the TIP ?? I don't see how that could be possible. How could there be a vacuum when the TIP is connected to the air intake box?
My understanding of the collapsing TIP is down to the standard TIP being pretty flimsy especially on the corrugated section when hot.
I also thought the PCV system was most active at idle?
Happy to stand corrected if I'm wrong.

 

[Prawn]

there is most definately a vacuum in the TIP, especially when under boost.

Assuming a 100% free flowing air filter, there would be very minimal/no vacuum, but as no air filter is free flowing, a vacuum is created.

it's the vacuum that causes the TIP to collapse, not heat, although it may well collapse easier when hot, it's most definately the vacuum. it it were heat it could collapse and stay collapsed when you pulled over and opened the bonnet, which generally, it isn't.

Anything that's sucking air at a great rate through a filter will create negative pressure behind the filter.

you're right about the PCV system being most active at idle usually, as in that situation there isn't a vacuum in the TIP, but there is in the inlet manifold, so it uses this vacuum source instead, and then switches to using the TIP vacuum under boost when the PCV check valve closes.

the way we have set up Daves car (and the way mine has run for some time) is to allow it to breath naturally at idle, and positively via the TIP under boost.

 

[Caesium]

I take it TIP is turbo intake pipe?

 

[pauldazzle]

I think we have to agree to differ on that one Prawn.
A vacuum is an empty space devoid of pressure or a space of lower than atmospheric pressure.
I can't see how the TIP could have a vacuum when it's sucking in air at a greater than atmospheric pressure.
I always thought that TIP collapse was due to the turbo sucking in air at high pressure causing the weak standard TIP to collapse. If it had a vacuum present it would surely stay collapsed when returning to no boost?

 

[Prawn]

Chris: TIP is indeed turbo intake pipe

I think you need to think about it a bit harder Paul, about what's under pressure and what's under vacuum.

On boost, everything after the turbo is under pressure.

In the TIP, the turbo is trying to suck air in through the air filter, which can never be 100% free flowing.

To simulate the arguement, take a coke bottle, and make a tiny hole in the bottom, then try and suck through the top.

if you suck slowly, you're able to draw air in, and the bottle holds it's shape. if you suck harder, air can still come in the bottom, but not at the same rate as you're trying to suck it out, so the bottle collapses in a little, and there is negative pressure inside the bottle.

that's exactly the same situation that occurs inside the TIP. Obviously not exactly like that, but the principle is the same....

This is why the TIP returns to it's original shape too, as naturally it wants to hold it's shape, but it's pulled in by the vacuum. When the vacuum is taken away, the pipe regains it's shape.

 

[pauldazzle]

Ok Prawn, I bow to your greater knowledge.

 

[Prawn]

haha. is that a sarcastic response? or does my analogy make sense?

I might see if I can rig up my boost gauge line into the TIP somehow, to try and either prove or destroy my idea.

 

[Welly]

To simulate the arguement, take a coke bottle, and make a tiny hole in the bottom, then try and suck through the top.

if you suck slowly, you're able to draw air in, and the bottle holds it's shape. if you suck harder, air can still come in the bottom, but not at the same rate as you're trying to suck it out, so the bottle collapses in a little, and there is negative pressure inside the bottle.

Nine analogy.

However, you seem to have got away from the original problem of the pressurised oil system... Which I am interested to know the cause of.

The key question is did it do it before? If yes, than whats changed. If the only change is the PCV pipe, then it must have something to do with it. The question is what....

Damn PCV pipes suck some serious monkey nuts, I've had them split on both the VAG engines I've owned!

 

[pauldazzle]

haha. is that a sarcastic response? or does my analogy make sense?

I might see if I can rig up my boost gauge line into the TIP somehow, to try and either prove or destroy my idea.

No sarcasm meant at all Prawn. I'm happy to learn.

Although I can understand your Coke bottle theory, I'm still baffled as to how that can be applied to the TIP though.

 

[Welly]

Just believe him mate, he is absolutely spot on.

TIPs on VAG 1.8T engines are renowned pulling themselves in under high boost, simply from the fact that the turbo is pulling more air then the pipe itself has the capacity to deliver... Call it a design flaw I guess, the pipe should be bigger really to stop this from happening.

Thats why there is a thriving trade in aftermarket silicone TIPs from Forge etc. Well, that and the K03S conversion!

 

[auroan]

Call it a design flaw I guess, the pipe should be bigger really to stop this from happening.

Thats why there is a thriving trade in aftermarket silicone TIPs from Forge etc. Well, that and the K03S conversion!

Erm why is it a design flaw ? What is it with people lambasting the engines etc when they "uprate" other components past the supporting components designed limits.

If you want more boost you put a better TIP in. The std TIP is perfect for a std car.

 

[Prawn]

No sarcasm meant at all Prawn. I'm happy to learn.

Although I can understand your Coke bottle theory, I'm still baffled as to how that can be applied to the TIP though.

You need to take scale out of the question to be able to appreciate it. the coke bottle analogy usese extremes of a TINY hole in 1 end and a big hole in the other end.

To give you a VERY rough idea of scale, a 700bhp F1 engine consumes around 650 LITRES of air every second, now imagine a baloon the size of 325 large coke bottles, all emptying through your air filter, in 1 second flat?

a typical MAF reading from an S3 may be around 200g/s, which as I understand it, is 200 grams of air every second.

so given the density of air (estimate at RTP) is around 1.2kg/m³, 200g/s would be 200/1200= 1/6, so the volume of air consumed at 200g/s would be 1000/6 = 166 litres per second.

Not quite as big as the F1 example, but much more realistic.

We all know air filters provide a resistance to flow of some sort, and any resistance to flow will result in negative pressure between the filter and the turbo intlet. the more restrictive the filter the more negative pressure will result in the TIP. likewise, the more boost (and thus air sucked in by the turbo) the more negative pressure as well. So you're much more likely to get a collapsed TIP on a remapped car with a standard airbox.


Anyway, back to the point.

One reason for custards pressurised crank case could be that the rest of his breather system is blocked, in which case plugging the hole could cause pressure, although i don't think it would, as the hose was still split further down, hence me telling him it was pointless to plug at all.

it could also be the rings having some blow by causing elevated pressure.

personally, I think it's custard being fussy. I personally heard almost no sound from the oil cap at all, and the test wasn't repeated at all either.

 

[pauldazzle]

I've fitted silicone TIP's on my last 2 Revo'd mk4 Golfs, & I'm well aware of the benefit. I've never actually experienced a collapse of the standard TIP, & fitted silicone TIP's to help with throttle response & reduce lag.
I can totally understand a vacuum being caused if the TIP collapses. but I've always thought that was as a symptom of collapse rather than a cause.

Back to the thread.
Is it possible that the reason for the split pipe is down to a blockage causing a pressure build up? Obviously if the split is before the bolt then the bolt can't be serving any real purpose, & is not responsible for the pressure build up.

 

[Prawn]

I can totally understand a vacuum being caused if the TIP collapses. but I've always thought that was as a symptom of collapse rather than a cause.

Back to the thread.
Is it possible that the reason for the split pipe is down to a blockage causing a pressure build up? Obviously if the split is before the bolt then the bolt can't be serving any real purpose, & is not responsible for the pressure build up.

the vacuum is indeed the cause of the collapse, although it obviously increases when the pipe collapses, as the diameter is reduced, reducing capacity.

I would imagine the pipe is split through age, and the fact that it's constantly been put under continously changing vacuum/boost conditions for the last 10 years! I've found this pipe split on almost every AGU I've seen.

As you say, the bolt is most definately not responsible for the pressure build up, as it's already split pre bolt. Custard just insisted on putting it in, because he didn't believe me!

 

[pauldazzle]

Thanks Prawn, interesting stuff.

 

[Custard]

The split in the pipe before where the bolt was, is closed up, you have to bend the pipe to open it up, or put it under boost pressure, its not guna let much crank case pressure out. But as i said earlier this is all speculation untill i remove the pipes and investigate.

I will also do a pressure test on the bores.

I wasn't being fussy! most of the pressure had already been released by the time i called Prawn.

 

[Caesium]

Right, anything air is drawn through that narrows, even slightly, will cause a low pressure area. That's a venturi.
A jet engine is open at the front, about as free flowing as you can get. They create such low pressure at the intake they will suck water off a runway 5 feet below them.

All air movement creates low pressure somewhere, the air by very virtue of it moving because as air moves somewhere, the atmosphere moves in to replace the air that has just moved elsewhere.

It makes sense that the PCV goes into the TIP (thanks prawn) as its the only negative section of the intake section while the engine is anywhere above idle.

 

[Prawn]

thing is though Dave, the pressure required for a noticable release from the oil cap, would have been WAY more than enough to force the split open in that hose.

As I said on msn, just because the two sides of the split visably touch when the pipe is in it's natural position, it'd still leak like hell under any form of pressure.