Blue Smoke From Exhaust

[willis 18 1 Cars]

I have a 1.6 GTI which up until recently I believed it needed new valve stem seals..........until I changed the exhaust. Once the engine had warmed, and only then, it produced blue smoke

 

It used to have a big bore system on and I replaced it for a standard one. Since then the smoke has disappeared, literally!

 

Now, I'm not complaining or anything, but I am trying to understand why. There is a lot of talk about back pressure, some people say you need it and others say that you don't and want as free-flowing exhaust as possible (when re-mapped etc.). I then came across the following link online which I found interesting and helps to explain some of it, but not all:

 

http://www.mellingengine.com/Portals/5/pdf/pdf_catalog/pressure-vs-flow.pdf

 

Once the engine is warm obviously the oil pressure drops so is it because it was dropping too low for the oil pump to work properly? If so then the oil pressure instrument was displaying everything was OK. I had to tinker with the idle speed as well, presumably due to the increased back pressure of the new exhaust.

 

Was this all due to the excessive flow resistance or is this a huge coincidence?

 

Answers on a postcard.

 

Thanks

[Hheppy 9 1 Cars]

Can't quite remember the reason myself, but if you watch the WheelDealer eposides where they do up a 205 GTI they had much the same issue I believe!

 

nice fix for you and I bet you can hear yourself think whilst driving now you have a standard exhaust on.

 

I did the same with mine last year, best thing I ever did :-)

[large 33]

I thought Ed changed the gear linkage to stop the engine from smoking.

 

Willis, I think you could be getting confused with the pressures.

Back pressure in the exhaust is referring to the gas flow and has nothing to do with oil pressure.

 

Once the engine is warm obviously the oil pressure drops so is it because it was dropping too low for the oil pump to work properly?

 

You are looking at this the wrong way the pump is responsible for delivering flow and pressure. A drop in pressure is because the oil is circulating with in the oil system with less restriction as the engine warmes up things expand also the oil losses viscosity (becomes thinner) so the amount of force needed to move the oil around the engine (pressure) drops.

 

I can't see why it has stopped smoking just keep a close eye on the oil level.

[willis 18 1 Cars]

Yeah, I checked the the oil last week and it was 2/3 between min & max.

 

I have searched quite a lot for the answer but all I could find, along with other possible causes for blue smoke (of which there are a few!) on several websites was:

 

Blue smoke = excessive flow resistance/big bore exhaust

[large 33]

Blue smoke is normally a sign that the engine is burning oil. Like you said valve stem seals HG and the like.

[welshpug 1,622]

What a fantastically descriptive thread title placed in the correct subforum for all to read...

[willis 18 1 Cars]

Do I detect a bit of sarcasm welshpug?

[Tom Fenton 1,525]

It is a bit duff you have to admit.

[Alan77 78 1 Cars]

What Large said...

[willis 18 1 Cars]

I'm sorry tom, but it's not like your laser post is in the restoration thread.

[Tamanga 6]

What a fantastically descriptive thread title placed in the correct subforum for all to read...

This doesn't help much to be fair pal. I've picked up on the fact there is a love of rules on here but where should this post have actually gone? It's hard to work out what goes where there are so many sub forums!

 

Thought I'd read somewhere that 'the philosophy of the forum is about sharing

unbiased, constructive and helpful knowledge, experience and information.'

 

Be that on forum etiquette or knowledge of 205s, your post contains neither, just a snotty and some what snide remark.

[Biggles 65]

 

It used to have a big bore system on and I replaced it for a standard one. Since then the smoke has disappeared, literally! is this a huge coincidence?

 

Answers on a postcard.

 

Thanks

 

The lower gas velocity (and probably lower gas temperature) from the big bore pipe just make the smoke (more) visible. Same principle as your breath on a cold day - exhale slowly and it's really visible - blow it out fast and it isn't.

[welshpug 1,622]

its pretty simple, its an 8v xu, that is smoking blue smoke.

 

a more appropriate place would be:

 

XU 8v Engine Maintenance and Performance Upgrades

Discussion about service/maintenance and performance upgrades of all 8v XU engines (including modified and forced induction ones, such as 2.0T).

 

 

And a thread title such as "blue smoke?" would gather far more prompt responses.

[GLPoomobile 958]

This doesn't help much to be fair pal. I've picked up on the fact there is a love of rules on here but where should this post have actually gone? It's hard to work out what goes where there are so many sub forums!

Thought I'd read somewhere that 'the philosophy of the forum is about sharing

unbiased, constructive and helpful knowledge, experience and information.'

Be that on forum etiquette or knowledge of 205s, your post contains neither, just a snotty and some what snide remark.

Sigh.

 

This may be so. But I'm a long time advocate of encouraging people to think about their topic titles. I see this on every forum. It's just bloody sloppy.

 

By it's very nature, most topics on these forums are some sort of question or request for help, so the topic title "a question" is about as redundant as you can get. What if we all did the same? You'd open the forum to see a page full of topics all with the title "a question". Were do you start? Do you read them all? Would there be any point in topic titles anymore?

 

This isn't me trying to be harsh or rude or unfriendly. But please, it's not difficult to spend a few moments thinking of some suitabke words that are relevant to the topic content. After all, if you come here expecting help, then help us help you.

 

Sorry I have nothing to say about the actual technical issue. Now back on topic.....

[dcc 855]

I can see nothing constructive is going to come of this thread...

 

So

 

[willis 18 1 Cars]

Thanks for everybody's constructive response.

 

I appreciate the title wasn't the best, but does it really matter? The fact is as Tamanga said I didn't know what to call it, where to put it and ultimately, it seems to have worked!

 

I work in retail and generally hate forums (I won't go into this now) but I really like this one for what it is - a great place to share knowledge and to get good and usually professional advice. Where else can you easily get that (with the exception of PSCUK) on one of these now rare cars?

 

I apologise for the title and where it has been put, but there is more to these cars and quite frankly more to life than moaning about things like this.

[Simes 248 2 Cars]

Moved for you.

Don't worry too much about it, we've all done it.

Enjoy the forum.

[willis 18 1 Cars]

Thanks Simes.