Hi, my 306 Meridian HDI front exhaust has come apart right at where the pipe is welded to the Cat. I have been quoted £250 to replace it. I have been reading on the net that some owners have just not bothered to replace the cat on diesels and have fitted a straight through pipe instead from the 'non cat models'. Apparently, a cat is not really needed?
My questions are... if I do this too, will it still pass the MOT emissions test? And will it be classed as a modified car for insurance purposes? What about performance, will this increase, decrease? And what affect on MPG?
What does this cat actually do (apart from cost us all lots of money when it goes)??
Is this a good idea, leaving the cat off?
Cheers
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The car will still pass the current emissions test - diesels are tested only for smoke opacity which is a pretty antiquated measure of emissions.
I'd imagine your insurance company would class it as a modification, but you may be able to argue its not performance enhancing and therefore they may not charge you.
Performance will probably increase marginally as the exhaust will flow more freely, but it won't be much. MPG should be unaffected.
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Cheers for that. But what about the Co2 emissions, aren't they affected by the cat?
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Yes, the CO2 will be lower, as some will remain as CO instead of being oxidised in the catalyst. The catalysts on diesels are a waste of time unless you sit in your car with a hosepipe from the exhaust in which case you'll die, like people used to do.
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I'm sorry I don't quite understand you. Are you saying the C02 is lower... with the Cat fitted, or without the Cat fitted?
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CO is fuel that hasn't burnt properly and so contans only one molecule of oxygen. Unfortunately CO is a much more damaging greenhouse gas than CO2. This is where the catalyst comes in. The catalyst converts the CO into CO2 by adding an extra oxygen molecule. So yes, if you remove the catalyst, CO2 emmisions decrease, but you pump more of the nasty CO gas into the air.
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mfarrow, I'm not sure where you get the idea that CO is >a much more damaging greenhouse gas than CO2<. The worry about global warming is from increasing CO2 levels, which have been measured accurately for about 100 years and are undisputably rising. CO2 is the 'natural' oxide of carbon, and CO will be converted to it by other oxidation processes after it emerges from an exhaust pipe. Cat converters are to reduce the toxic level of CO in urban atmospheres - and to make it harder for people to kill themselves with a hose.
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>>The catalysts on diesels are a waste of time unless you sit in your car with a hosepipe from the exhaust in which case you'll die,
If they prevent death by suicide.then they are not a waste of time..In answer to previous question. if you have a cat fitted would suggest you replace..Manufacturers dont fit for no reason.
if you think they do.replace with what you want..though would speak to insurance co before doing so..Also let DVLA know it may change your tax band
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Steve
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This will have no effect on insurance. Don't even bother telling them.
Some 306 models, around 1996, some had cats, others didn't.
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groups.msn.com/honestjohn - Pictures say a thousand words.....
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Agree carbon dioxide isn't a greenhouse gas because it is unstable and converts to CO2 in the atmosphere. Purpose of the diesel oxidation catalyst is mostly to reduce emission of CO and HC (unburnt fuel) from the exhaust.
Unfortunately they also increase emissions of nitrous oxides which is a much more potent greenhouse gas than carbon dioxide. They also increase fuel consumption by around 0.5% (according to the data i have) and so increase CO2 emissions.
So i would summise that diesel catalyst removal is advantageous from the point of view of conserving fuel resources and reducing greenhouse gases but probably a bad thing for local air quality.
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I get a feeling that there aren't too many scientists involved in this CO / CO2 discussion! I'm a chemist by trade, just for the record.
A cat cannot prevent suicide by hosepipe. When someone does the hosepipe routine, they'll die whatever the exhaust content. Sure, CO is very poisonous and will kill quickly. However, if the content is mainly CO2 then they'll just die through asphyxiation. Any gas other than pure O2 is 'poisonous' in this sense - if the surrounding atmosphere is 100% something else, then there is no oxygen to breathe and you die! Only a very small number of gases are actually poisonous in the strict sense of the word - most are simply asphyxiating.
I believe the main purpose of cats is more to do with unpleasant oxides of sulphur than the CO / CO2 ratio.
Incidentally, CO is quite a stable gas. The carbon-oxygen triple bond is rather hard to break, and for this reason the lone election on the carbon tends to attact something more electronegative than just another oxygen atom.
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"The worry about global warming is from increasing CO2 levels, which have been measured accurately for about 100 years and are undisputably rising."
I'm not a scientist either, but to suggest that 100 years of measuring is sufficient to draw reliable conclusions from with regard to global warming seems to me to be jumping to conclusions rather too quickly considering the changes in global temps in the last 1000 years let alone the last 10,000 or 100,000. I would also like to know whether car exhausts make much of a contribution to that rise in CO2 levels?
My next question would be which is cause and which is effect? Do we definitely know that CO2 is causing global warming or is the rise in CO2 the result of rising temps? Does anyone REALLY know the answers?
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The rise in CO2 and CO levels and for that matter OC2, 2OC or whatever is directly proportional to the amount of money the government can extract from us for its alleged alleviation.
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Lets look at the emissions / global warming issue from a scientific standpoint.
If you graph the average surface air temperature of the earth over tens or hundreds of thousands of years, it fluctuates up and down - much like a conventional sine wave. At the moment (and probably for a long time yet), we just happen to be on the up-slope of this graph.
We cannot prevent average temperatures rising, it is due to massive geothermal and celestial forces way beyond our control. The gaseous emissions of the human race make no difference at all - they are far to small. Money would be better spent adapting to the rising temperatures, rather than on futile attempts to prevent the inevitable.
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Sorry, Phil - you misunderstood my remark. I wasn't trying to say that CO2 was causing global warming (and I don't think I did say that). You are welcome to believe the two are not connected. But if you do, I suspect that may be because you want to, rather than because the evidence is inadequate. The connection may not be proved, but I think the data are indisputable.
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"You are welcome to believe the two are not connected. But if you do, I suspect that may be because you want to, rather than because the evidence is inadequate. The connection may not be proved, but I think the data are indisputable."
Andrew, it depends what you read doesn't it?
Quote:- "carbon dioxide -- often thought of as a key "greenhouse gas" -- is not the cause of global warming. The opposite is most likely to be true, according to Robert Essenhigh, E.G. Bailey Professor of Energy Conservation in Ohio State's Department of Mechanical Engineering. It is the rising global temperatures that are naturally increasing the levels of carbon dioxide, not the other way around, he says."
Full article is here
www.sciencedaily.com/releases/2001/06/010615071248...m
I don't know if it is true or not - I'm not qualified to say - but who does know the truth? Problem is that for every piece of evidence that suggests we are increasing the Greenhouse effect by our emissions of Greenhouse gases there is someone who says the opposite.
The other day I read an artcle saying that increasing temps were causing ice in Antarctica to melt faster than ever and then another article saying that temps in Antarctica were getting lower causing glaciers to flow faster hence more ice was flowing into the ocean and breaking off as icebergs.
Who knows what to believe except that taking all cars off the road would probably make little difference to CO2 levels since 95% of CO2 occurs through natural processes - or is that wrong too? I really don't know what to believe - but I know I don't believe much of what politicians say about the subject.
Regards
Phil
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GF1 - please explain to me a >carbon-oxygen triple bond< - I'm also (was) a chemist by trade, and I always thought O could manage no more than a double bond?
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Spare electron on the carbon atom I believe.
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Actually I'm talking out my wastegate here...
Just a dipole attaction to the next molecule that keeps it together - no 3rd covalent bond. Apologies.
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The same thing happened to mine at around 37000 miles and when examined it was easy to see why-the metal is so thin at that point.A friend of mine who performs the m.o.t. told me that a cat was not necessary on this engine, however we could not find a supplier of a non-cat piep that would fit my car (2000 model). We managed to get a pipe including a cat for £147. This is in the Middlesbrough area. Hope this helps, Regards.
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Cheers Paul. Well was still debating fitting a 'non cat' front pipe until I managed to find a guy who says he can weld it for £25-£30. Going to take it to him tomorrow. Will let you lot know how successful this turns out to be. If the weld fails I will try to get a garage to fit a non cat pipe. But I suspect that will be difficult. Its been a big enough job finding a garage that will weld it...they all want me to buy a nice expensive cat!
Can I just say what an excellent forum and website this is.....loads of really helpful knowledgable people on here.
Can't believe I haven't found this earlier
Cheers guys
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